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Dynamical Role of Light Neutral Leptons in Cosmology

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Abstract

Using the Vlasov equation, we show that massive galactic halos cannot be composed of stable neutral leptons of mass < or approx. = 1 MeV. Since most of the mass in clusters of galaxies probably consists of stripped halos, we conclude that the ''missing mass'' in clusters does not consist of leptons of mass < or approx. = 1 MeV (e.g., muon or electron neutrinos). Lee and Weinberg's hypothetical heave leptons (mass approx. = 1 GeV) are not ruled out by this argument.

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... For example, the Bullet cluster places limits on the self interaction cross section of dark matter particles to σ/m < 1 cm 2 g −1 [2]. If dark matter particles are fermionic and too light, m 400 eV then their Fermi pressure does not allow structure to form (the Tremaine-Gunn bound [3]). Other constraints come from the clustering seen in the Lyman-α forest, for which a comparison with hydrodynamical simulations leads to a bound of m > 3.3 keV at 2σ [4]. ...
... If the DM decoupled together with the neutrinos, we have g dec * = 10.75 and m > 70 eV. This is a much weaker bound than the Tremaine-Gunn bound requiring that m > 400 eV in order for the gravitational well of galaxies to overcome the Fermi pressure [3]. On the other hand, constraints from the Lyman α forest require that m > 3.3 keV so that the power spectrum remains sufficiently unsuppressed at scales up to k ∼ 10h Mpc −1 [4]. ...
... Although very low compared to the typical scenarios where m ∼ 100 GeV, such low masses are not incompatible with technical requirements: the freeze-out occurs before recombination, the mass of the mediator is much larger than m and yet non-relativistic during BBN. Yet again, we must stress that the Tremaine-Gunn bound of m > 400 eV for fermions remains stronger [3]. The constraints from the Bullet cluster [2] do not restrict the parameter space in this region and the lightness of the DM would mean that it cannot decay to leptons, but only to photons, making such models compatible with the heating of the intergalactic medium [53]. ...
Preprint
We use large-scale cosmological observations to place constraints on the dark-matter pressure, sound speed and viscosity, and infer a limit on the mass of warm-dark-matter particles. Measurements of the cosmic microwave background (CMB) anisotropies constrain the equation of state and sound speed of the dark matter at last scattering at the per mille level. Since the redshifting of collisionless particles universally implies that these quantities scale like a2a^{-2} absent shell crossing, we infer that today w(DM)<1010.0w_{\rm (DM)}< 10^{-10.0}, cs,(DM)2<1010.7c_{\rm s,(DM)}^2 < 10^{-10.7} and cvis,(DM)2<1010.3c_{\rm vis, (DM)}^{2} < 10^{-10.3} at the 99%99\% confidence level. This very general bound can be translated to model-dependent constraints on dark-matter models: for warm dark matter these constraints imply m>70m> 70 eV, assuming it decoupled while relativistic around the same time as the neutrinos; for a cold relic, we show that m>100m>100 eV. We separately constrain the properties of the DM fluid on linear scales at late times, and find upper bounds cs,(DM)2<105.9c_{\rm s, (DM)}^2<10^{-5.9}, cvis,(DM)2<105.7c_{\rm vis, (DM)}^{2} < 10^{-5.7}, with no detection of non-dust properties for the DM.
... We, in this article, seek a possibility for a sterile RHN to make up the whole DM in the Universe and, in particular, propose the new production mechanism of sterile RHN DM through the mixing among RHNs. This is in contrast to the conventional mechanisms requiring the sterile RHN DM to couple to left-handed neutrinos which suffer from the severe tension between the bounds from the X-ray observation and the small-scale structure data [10][11][12][13][14][15]. These constraints, however, heavily depend on their production mechanisms and many possibilities have been explored to produce the desired DM abundance in addition to the conventional nonresonant/resonant active-sterile neutrino conversion mechanisms [6][7][8][9][16][17][18][19][20]. ...
... On the other hand, since Θ 2 11 depends on θ N and we need a relatively large θ N for our scenario to work, the N 1 is subject to the X-ray constraint given by Θ 2 11 10 −5 (keV/M 1 ) 5 [12]. One may simply expect that the X-ray bound is easily circumvented because the Yukawa coupling of ν R1 can be negligibly small. ...
... We can consider the decay of N 2 (and/or N 3 ) which is thermally decoupled while it is relativistic (otherwise N 2 number density would be too small due to the Boltzmann suppression). N 1 abundance then can be estimated as Ω N1 h 2 10 −10 Θ 2 11 10 −12 ...
Preprint
We study a scenario where sterile neutrino (either warm or cold) dark matter (DM) is produced through (nonresonant) oscillations among right-handed neutrinos (RHNs) and can constitute the whole DM in the Universe, in contrast to the conventional sterile neutrino production through its mixing with the left-handed neutrinos. The lightest RHN can be sterile neutrino DM whose mixing with left-handed neutrinos is sufficiently small while heavier RHNs can have non-negligible mixings with left-handed neutrinos to explain the neutrino masses by the seesaw mechanism. We also demonstrate that, in our scenario, the production of sterile RHN DM from the decay of a heavier RHN is subdominant compared with the RHN oscillation production due to the X-ray and small-scale structure constraints.
... If dark matter is made of elementary particles, the corresponding particle should be massive (to form over-densities in process of gravitational collapse), long-lived (to be stable for at least the age of the Universe) and neutral with respect to strong and electromagnetic interactions (to be sufficiently 'dark'). The only known massive, long-lived and neutral particles are the usual (left-handed) neutrinos, but they are too light to form small dark matter haloes [26,27]. As a result, the hypothesis of dark matter particle implies an extension of the Standard Model of particle physics. ...
... Sterile neutrinos decay possess the 2-body radiative channel N → γ + ν, so the observation of ∼3.5 keV decay line would imply the existence of light sterile neutrino dark matter particles with mass ∼7.1 keV. The simplest production scenario of sterile neutrino dark matter -via non-resonant oscillations of usual (active) neutrinos in the early Universe [31][32][33][124][125][126] -is already excluded by the combination of X-ray measurements [51], measurements of Lymanα forest [127][128][129][130][131][132] and the phase-space bound from dwarf spheroidal galaxies [26,[133][134][135][136]. The realistic scenario of dark matter production within the νMSM now involves resonant oscillations of active neutrinos in hot primeval plasma with significant lepton asymmetry generated by decays of heavier sterile neutrinos [137][138][139][140][141]. The parameters of observed ∼3.5 keV line are consistent with νMSM predictions, see Fig. 7 for details. ...
Preprint
The detection of an unidentified emission line in X-ray spectra of cosmic objects would be a 'smoking gun' signature for particle physics beyond the Standard Model. More than a decade of its extensive searches results in several narrow faint emission lines reported at 3.5, 8.7, 9.4 and 10.1 keV. The most promising of them is the emission line at ~3.5 keV reported in spectra of several nearby galaxies and galaxy clusters. Here I summarize its up-to-date status, overview its possible interpretations, including an intriguing connection with radiatively decaying dark matter, and outline future directions for its studies.
... In the simplest sterile neutrino scenarios, it is assumed that the abundance of sterile neutrinos ν s is zero at the end of inflation, and they are later produced through their mixing with SM (active) neutrinos ν a [3,4] (see also [5][6][7]). Experimental constraints on the mass of keV sterile neutrinos and their mixing with SM neutrinos arise from the measured DM relic density [8,9], from Pauli blocking (the Tremaine-Gunn bound) [10,11], from Lyman-α forests [12][13][14], and from X-ray searches for radiative decays of sterile neutrinos ν s → ν a + γ [15][16][17][18][19][20]. From the combination of these constraints, one concludes that the ν s mass should be m s 4 keV, and its mixing angle with the SM neutrinos should be sin 2 2θ 10 −6 in the simple two-flavor approximation. ...
... We consider a simplified two-flavor oscillation picture with mixing between a sterile neutrino 1 ν s and one species of active neutrinos ν x , x = µ or τ . We do not consider mixing between ν s and electron neutrinos to avoid complications arising from charged current interactions FIG. 1. Supernova bounds on the sterile neutrino mass ms and mixing sin 2 2θ (orange, this work) between νx (x = µ or τ ) and νs flavors compared to previous constraints [17][18][19] from the Tremaine-Gunn bound [10,11] (yellow), from NuS-TAR observation of Galactic center [33] (pale orange), from X-ray searches in the Andromeda Galaxy M31 [15] (green), from the Fermi GBM all-sky analysis [34] (purple), and from the galactic [17] (dark blue) and extragalactic [16,18,19] (gray) diffuse X-ray background. For the latter constraint, we show also how it is modified if sterile neutrinos account for only a fraction of the DM in the Universe. ...
Preprint
We study the production of sterile neutrinos in supernovae, focusing in particular on the keV--MeV mass range, which is the most interesting range if sterile neutrinos are to account for the dark matter in the Universe. Focusing on the simplest scenario in which sterile neutrinos mixes only with muon or tau neutrino, we argue that the production of keV--MeV sterile neutrinos can be strongly enhanced by a Mikheyev--Smirnov--Wolfenstein (MSW) resonance, so that a substantial flux is expected to emerge from a supernova, even if vacuum mixing angles between active and sterile neutrinos are tiny. Using energetics arguments, this yields limits on the sterile neutrino parameter space that reach down to mixing angles of the order of sin22θ1014\sin^2 2\theta \lesssim 10^{-14} and are up to an order of magnitude stronger than those from X-ray observations. While supernova limits suffer from larger systematic uncertainties than X-ray limits they apply also to scenarios in which sterile neutrinos are not abundantly produced in the early Universe. We also compute the flux of O(MeV)\mathcal{O}(\text{MeV}) photons expected from the decay of sterile neutrinos produced in supernovae, but find that it is beyond current observational reach even for a nearby supernova.
... Observational data of astrophysical systems, including individual, groups and clusters of galaxies, and the universe in a cosmological context, show that in order to maintain the standard gravitational field equations of general relativity, including their Newtonian nonrelativistic weak field limit, it is necessary to postulate the existence a new kind of non-baryonic dark matter [12][13][14][15][16][17][18][19][20][21][22][23]. Although, current research is usually done assuming the existence of this non-detected dark matter, the alternative scenario consists on changing the field equations of gravitation at those scales. ...
... In order to obtain an equation that relates the curvature R with the trace T of the energy-momentum tensor, eq. (20) must be substituted into (19). Since this procedure yields a complex equation, we will tackle the problem in a different manner. ...
Preprint
We construct a relativistic metric description of MOND using the Palatini formalism following the f(χ)=χb f(\chi)=\chi^b description of \citet{mendozatula}. We show that in order to recover the non-relativistic MOND regime where, for circular orbits the Tully-Fisher law replaces Kepler's third law, the value of the parameter b=3/2 b = 3/2 , which is coincident with the value found using a pure metric formalism Capozziello et al. (2011). Unlike the pure metric formalism, which yields 4th order field equations, the Palatini approach yields second order field equations, which is a desirable requirement from a theoretical perspective. Thus, the phenomenology associated to astrophysical phenomena with Tully-Fisher scalings can be accounted for using this proposal, without the need to introduce any non-baryonic dark matter particles.
... For example, DM must be dark, meaning that it does not interact too readily with ordinary matter, and it needs to be matter, implying that it dilutes and gravitates like non-relativistic matter in the early universe. Observations of certain astrophysical structures imply further that the DM must not interact too strongly with itself, and have a mass greater than about m DM ≳ 10 −19 eV if it is a boson [11][12][13] and m DM ≳ 1 keV if it is a fermion [14,15]. ...
... DM comes from the mostly singlet neutrino mass eigenstate defined by ν 4 = ν s cos θ + ν a sin θ, where θ is the mixing parameter. To act as a fermionic DM species, the sterile neutrino ν 4 must satisfy the Tremaine-Gunn bound [14,15,121] which requires it to be heavier than about a keV. ...
Preprint
Full-text available
Astrophysical observations suggest that most of the matter in the cosmos consists of a new form that has not been observed on Earth. The nature and origin of this mysterious dark matter are among the most pressing questions in fundamental science. In this review we summarize the current state of dark matter research from two perspectives. First, we provide an overview of the leading theoretical proposals for dark matter. And second, we describe how these proposals have driven a broad and diverse global search program for dark matter involving direct laboratory searches and astrophysical observations. This review is based on a Green Paper on dark matter prepared as part of the 2020 Astroparticle Community Planning initiative undertaken by the Canadian Subatomic Physics community but has been significantly updated to reflect recent advances.
... There is still lot of parameter space left un-excluded for m a ≳ 0.3 MeV, g ae ≲ 6 × 10 −4 which can be probed by this boosted DM with m χ < 1 MeV. We restrict our analysis for DM masses down to m χ ≥ 1 keV, as lighter fermion DM is forbidden by Pauli exclusion principle [71]. The blazarboosted DM flux from BL Lacertae has less kinetic energy than TXS 0506+56, leading to weaker constraints coming from the former one. ...
Preprint
Full-text available
The trouble in detecting low mass dark matter due to its low kinetic energy can be ameliorated in the boosted dark matter framework, where a sub-population of galactic dark matter attains very high energy after being up-scattered by energetic standard model particles. However, in such a scenario the upper limits on the cross-section obtained hitherto are typically large. Hence in the minimal extension of standard model where new mediators act as a portal between the dark and visible sectors, the direct detection limits for sub-GeV dark matter might lie within the exclusion region of other ground based searches of the mediator. To evade this deadlock, we allude to blazar boosted dark matter electron scattering in multi-ton neutrino detector Super kamiokande. We consider minimal models such as axion like particle (ALP) and vector portal dark matter being upscattered by high energy blazar jet and analyse the interesting parameter reaches from Super kamiokande in the parameter space of the mediator, surpassing the existing constraints. Besides, this scenario exhibits stronger limits for previously unexplored ALP mediated sub-MeV dark matter search which is difficult due to associated momentum suppression.
... Insisting on such small values of Λ restricts the range of phenomenologically viable DM candidates that can also have sizable CP violating interactions with the axion. In particular, for fermionic DM, the Tremaine-Gunn bound [64] requires m χ ≳ keV ≫ Λ. Additionally, to avoid the hidden sector gauge group being in the deconfined phase in the galaxy requires the typical inter-DM spacing n −1=3 χ ≫ Λ −1 . ...
Article
Full-text available
An ultralight axion with C P violating interactions with a dark sector and C P preserving interactions with the visible sector can act as a novel portal between dark matter and the Standard Model. In such theories, dark matter sources an axion field extending over the entire galaxy, the gradient of which can be searched for with precise spin precession experiments. A reinterpretation of existing co-magnetometer data already constrains theories that are consistent with astrophysical bounds, and near-future experiments will begin probing well-motivated models. The required interactions can arise from a confining hidden sector without necessitating fine-tuning of the axion’s mass. Published by the American Physical Society 2025
... We derive expressions for both mechanisms, focusing on bosonic HDM. This choice is motivated by practical considerations; for fermionic relics, the Pauli-exclusion principle and Liouville's theorem restrict the density in halos from greatly exceeding the cosmic density [20]. ...
Preprint
Cosmologically stable, light particles that came into thermal contact with the Standard Model in the early universe may persist today as a form of hot dark matter. For relics with masses in the eV range, their role in structure formation depends critically on their mass. We trace the evolution of such hot relics and derive their density profiles around cold dark matter halos, introducing a framework for their indirect detection. Applying this framework to axions -- a natural candidate for a particle that can reach thermal equilibrium with the Standard Model in the early universe and capable of decaying into two photons -- we establish stringent limits on the axion-photon coupling gaγg_{a \gamma} using current observations of dwarf galaxies, the Milky Way halo, and galaxy clusters. Our results set new bounds on hot axions in the O(110)\mathcal{O}(1-10)\,eV range.
... Spergel & Steinhardt 2000) or a small enough DM particle mass (e.g. Tremaine & Gunn 1979) could prevent cusps to form. Yet, Macciò et al. (2012) argue that a particle mass small enough to produce core sizes of r c ∼ 1 kpc, as measured e.g. for the Fornax dwarf galaxy (Amorisco et al. 2013), is in contradiction to the constraints set by the large scale structure and would prevent the dwarf galaxy to form in the first place. ...
Preprint
We use high-resolution N-body simulations to study the effect of a galactic disc on the dynamical evolution of dark matter substructures with orbits and structural parameters extracted from the Aquarius A-2 merger tree (Springel et al. 2008). Satellites are modelled as equilibrium N-body realizations of generalized Hernquist profiles with 2×1062\times10^6 particles and injected in the analytical evolving host potential at zinfallz_\mathrm{infall}, defined by the peak of their mass evolution. We select all substructures with M200(zinfall)108MM_{200}(z_\mathrm{infall})\geq 10^8\,\mathrm{M_\odot} and first pericentric distances rp<r200r_p<r_{200}. Motivated by observations of Milky Way dwarf spheroidal galaxies, we also explore satellite models with cored dark matter profiles with a fixed core size rc=0.8asr_c=0.8\,a_s where asa_s is the Hernquist scale radius. We find that models with cuspy satellites have twice as many surviving substructures at z=0 than their cored counterparts, and four times as many if we only consider those on orbits with rp0.1r200r_p\lesssim0.1\,r_{200}. For a given profile, adding an evolving disc potential reduces the number of surviving substructures further by a factor of 2\lesssim2 for satellites on orbits that penetrate the disc (rp20kpcr_p\lesssim 20\,\mathrm{kpc}). For large rpr_p, where tidal forces and the effect of the disc become negligible, the number of satellites per pericentre bin converges to similar values for all four models.
... A second option consists in measuring or constraining generic properties of dark matter from astrophysical or cosmological observations. For example, assuming that the dark matter is made of fermions, then es-timations of their phase-space density in dwarf galaxies imply the Tremaine-Gunn bound (Tremaine & Gunn 1979) on their mass, m 400 eV. Such a bound does not apply for bosonic particles. ...
Preprint
If a significant fraction of the dark matter in the Universe is made of an ultra-light scalar field, named fuzzy dark matter (FDM) with a mass mam_a of the order of 1022102110^{-22}-10^{-21} eV, then its de Broglie wavelength is large enough to impact the physics of large scale structure formation. In particular, the associated cut-off in the linear matter power spectrum modifies the structure of the intergalactic medium (IGM) at the scales probed by the Lyman-α\alpha forest of distant quasars. We study this effect by making use of dedicated cosmological simulations which take into account the hydrodynamics of the IGM. We explore heuristically the amplitude of quantum pressure for the FDM masses considered here and conclude that quantum effects should not modify significantly the non-linear evolution of matter density at the scales relevant to the measured Lyman-α\alpha flux power, and for ma1022m_a \geq 10^{-22} eV. We derive a scaling law between mam_a and the mass of the well-studied thermal warm dark matter (WDM) model that is best adapted to the Lyman-α\alpha forest data, and differs significantly from the one infered by a simple linear extrapolation. By comparing FDM simulations with the Lyman-α\alpha flux power spectra determined from the BOSS survey, and marginalizing over relevant nuisance parameters, we exclude FDM masses in the range 1022ma<2.3×102110^{-22} \leq m_a < 2.3\times 10^{-21} eV at 95 % CL. Adding higher-resolution Lyman-α\alpha spectra extends the exclusion range up to 2.9×10212.9\times 10^{-21} eV. This provides a significant constraint on FDM models tailored to solve the "small-scale problems" of Λ\LambdaCDM.
... A thorough study by [20] attempted to estimate the minimum mass of SNs in dwarf spheroidals by taking the average stellar velocity dispersions (VDs), assuming the SNs have the same VD and applying the Tremaine-Gunn inequality [21], discussed in §3. 3. In that study, the kinematic data of the dSphs was limited to central velocity dispersions (VDs) of a handful of stars, leaving a degeneracy with the velocity anisotropy. ...
Preprint
We use dwarf spheroidal galaxies as a tool to attempt to put precise lower limits on the mass of the dark matter particle, assuming it is a sterile neutrino. We begin by making cored dark halo fits to the line of sight velocity dispersions as a function of projected radius (taken from Walker et al. 2007) for six of the Milky Way's dwarf spheroidal galaxies. We test Osipkov-Merritt velocity anisotropy profiles, but find that no benefit is gained over constant velocity anisotropy. In contrast to previous attempts, we do not assume any relation between the stellar velocity dispersions and the dark matter ones, but instead we solve directly for the sterile neutrino velocity dispersion at all radii by using the equation of state for a partially degenerate neutrino gas (which ensures hydrostatic equilibrium of the sterile neutrino halo). This yields a 1:1 relation between the sterile neutrino density and velocity dispersion, and therefore gives us an accurate estimate of the Tremaine-Gunn limit at all radii. By varying the sterile neutrino particle mass, we locate the minimum mass for all six dwarf spheroidals such that the Tremaine-Gunn limit is not exceeded at any radius (in particular at the centre). We find sizeable differences between the ranges of feasible sterile neutrino particle mass for each dwarf, but interestingly there exists a small range 270-280eV which is consistent with all dSphs at the 1-σ\sigma level.
... However, it soon became clear that neutrinos were not a good dark matter candidate for two reasons. The first argument is based on the limited phase space for neutrinos gravitationally bound to a galaxy (Tremaine and Gunn, 1979). As a consequence, if massive neutrinos are supposed to be the dark matter in galaxies, they must obey a lower mass limit of some 30 eV for typical spirals, and even 100-200 eV for dwarf galaxies. ...
Preprint
The case for small neutrino mass differences from atmospheric and solar neutrino oscillation experiments has become compelling, but leaves the overall neutrino mass scale m_nu undetermined. The most restrictive limit of m_nu < 0.8 eV arises from the 2dF galaxy redshift survey in conjunction with the standard theory of cosmological structure formation. A relation between the hot dark matter fraction and m_nu depends on the cosmic number density n_nu of neutrinos. If solar neutrino oscillations indeed correspond to the favored large mixing angle MSW solution, then big-bang nucleosynthesis gives us a restrictive limit on all neutrino chemical potentials, removing the previous uncertainty of n_nu. Therefore, a possible future measurement of m_nu will directly establish the cosmic neutrino mass fraction Omega_nu. Cosmological neutrinos with sub-eV masses can play an interesting role for producing the highest-energy cosmic rays (Z-burst scenario). Sub-eV masses also relate naturally to leptogenesis scenarios of the cosmic baryon asymmetry. Unfortunately, the time-of-flight dispersion of a galactic or local-group supernova neutrino burst is not sensitive in the sub-eV range.
... Among these observations, the most remarkable pieces of evidence are, among others, the presence of DM in the Coma [26,27] and Bullet Clusters [28,29], the flat galactic rotation curves [30,31], gravitational lensing [32], Nucleosynthesis abundances, the Cosmic Microwave Background (CMB) anisotropies and the growth of large structures [33]. From these pieces of evidence, some properties of DM can be inferred: namely, that it has to be nonrelativistic at the moment of decoupling [34], be it stable or long-lived [35,36], effectively non-photon-interacting [37], collisionless [38], dissipationless [39], smoothly distributed at cosmological scales [40] and sufficiently heavy [41]. These evidences, together with the assumption of the particle nature of DM and the constraints of thermal decoupling, support one of the most suitable candidates for DM, the so-called Weakly Interactive Massive Particles (WIMPs). ...
Preprint
In the following work, we compute the positron production from branon dark matter annihilations in order to constrain extra-dimensional theories. By having assumed that the positron fraction measured by AMS-02 is well explained just with astrophysical sources, exclusion diagrams for the branon mass and the tension of the brane, the two parameters characterising the branon phenomenology become possible. Our analysis has been performed for a minimal and a medium diffusion model in one extra dimension for both pseudo-isothermal and Navarro Frenck White dark matter haloes. Our constraints in the dark matter mass candidate range between 200 GeV and 100 TeV. Combined with previous cosmological analyses and experimental data in colliders, it allows us to set bounds on the parameter space of branons. In particular, we have discarded regions in the mass-tension diagram up to a branon mass of 28 TeV for the pseudo-Isothermal prole and minimal diffusion, and 63 TeV for the Navarro-Frenck-White profile and medium diffusion.
... Third, if the sterile neutrinos compose a significant part of the DM, Ω N Ω DM , one has to take into account bounds from the structure formation, arriving from the relative abundance of dwarfs and other small satellite galaxies [25], phase space density of galactic dark matter [26], and analyses of Lyman-α forest [27]. These bounds constrain the level of free streaming in the dark matter, so they actually limit the average velocity of the dark matter particles. ...
Preprint
We study a model of a keV-scale sterile neutrino with a relatively large mixing with the Standard Model sector. Usual considerations predict active generation of such particles in the early Universe, which leads to constraints from the total Dark Matter density and absence of X-ray signal from sterile neutrino decay. These bounds together may deem any attempt of creation of the keV scale sterile neutrino in the laboratory unfeasible. We argue that for models with a hidden sector coupled to the sterile neutrino these bounds can be evaded, opening new perspectives for the direct studies at neutrino experiments such as Troitsk ν\nu-mass and KATRIN. We estimate the generation of sterile neutrinos in scenarios with the hidden sector dynamics keeping the sterile neutrinos either massless or superheavy in the early Universe. In both cases the generation by oscillations from active neutrinos in plasma is suppressed.
... The requirement that the phase-space density of the DM does not exceed that of the degenerate Fermi gas leads to a lower mass bound. For a spherically symmetric object, the bound reads [122] ...
Preprint
We consider the implications of a shared production mechanism between the baryon asymmetry of the universe and the relic abundance of dark matter, that does not result in matching asymmetries. We present a simple model within a two sector leptogenesis framework, in which right handed sterile neutrinos decay out of equilibrium to both the Standard Model and the dark sector, generating an asymmetry in one and populating the other. This realization naturally accommodates light dark matter in the keV mass scale and above. Interactions in the dark sector may or may not cause the sector to thermalize, leading to interesting phenomenological implications, including hot, warm or cold thermal relic dark matter, while evading cosmological constraints. Under minimal assumptions the model provides a novel non-thermal production mechanism for sterile neutrino dark matter and predicts indirect detection signatures which may address the unexplained 3.5 keV line observed in various galaxy clusters.
... This is a self-consistent condition for a sufficiently heavy, weakly coupled dark matter satisfying the overclosure constraint in general, and here in particular in regions allowed by the much more stringent isocurvature constraint. Indeed, when ψ is the dark matter particle, its mass is bounded from below by the Tremaine-Gunn limit [45,46] m ψ > ∼ 0.1 keV. ...
Preprint
We consider portal models which are ultraweakly coupled with the Standard Model, and confront them with observational constraints on dark matter abundance and isocurvature perturbations. We assume the hidden sector to contain a real singlet scalar s and a sterile neutrino ψ\psi coupled to s via a pseudoscalar Yukawa term. During inflation, a primordial condensate consisting of the singlet scalar s is generated, and its contribution to the isocurvature perturbations is imprinted onto the dark matter abundance. We compute the total dark matter abundance including the contributions from condensate decay and nonthermal production from the Standard Model sector. We then use the Planck limit on isocurvature perturbations to derive a novel constraint connecting dark matter mass and the singlet self coupling with the scale of inflation: mDM/GeV0.2λs3/8(H/1011GeV)3/2m_{\rm DM}/{\rm GeV}\lesssim 0.2\lambda_{\rm s}^{\scriptscriptstyle 3/8} \left(H_*/10^{\scriptscriptstyle 11}{\rm GeV}\right)^{\scriptscriptstyle -3/2}. This constraint is relevant in most portal models ultraweakly coupled with the Standard Model and containing light singlet scalar fields.
... This is the wellknown fact that in a low-energy effective theory that includes one or more light fundamental scalars (as likely is the SM with a Higgs boson), one expects enormous quantum corrections to the scalar's mass from the physics in the UV (the Planck scale, in the absence of anything else). Given the broad separation between the characteristic energies in play, this means that in order to get electroweak symmetry breaking (EWSB) one should fine tune the fundamental (unknown) Lagrangian parameters at the level -again in the absence of anything lighter than the Planck scale -of one part in ∼ 10 28 . Unless, of course, additional degrees of freedom were present, preferably close to the Higgs mass itself (say ∼ 100 − 1000 GeV). ...
Preprint
We give a brief review of the current constraints and prospects for detection of higgsino dark matter in low-scale supersymmetry. In the first part we argue, after performing a survey of all potential dark matter particles in the MSSM, that the (nearly) pure higgsino is the only candidate emerging virtually unscathed from the wealth of observational data of recent years. In doing so by virtue of its gauge quantum numbers and electroweak symmetry breaking only, it maintains at the same time a relatively high degree of model-independence. In the second part we properly review the prospects for detection of a higgsino-like neutralino in direct underground dark matter searches, collider searches, and indirect astrophysical signals. We provide estimates for the typical scale of the superpartners and fine tuning in the context of traditional scenarios where the breaking of supersymmetry is mediated at about the scale of Grand Unification and where strong expectations for a timely detection of higgsinos in underground detectors are closely related to the measured 125 GeV mass of the Higgs boson at the LHC.
... Since ∆ can be made arbitrarily small, the DM mass can in principle be lowered even far below the keV scale. If DM is a fermion, there still exists a lower mass bound of order hundreds of eV that holds independently of the production mechanism simply due to Fermi-Dirac statistics [37] (for an updated analysis using various assumptions see, e.g., [38]); for bosonic DM on the other hand, we can apparently make DM arbitrarily light if ∆ is tiny. We stress that this is qualitatively different from the socalled misalignment mechanism, popularized through axion DM [39], which uses classical field oscillations to obtain cold DM [40]. ...
Preprint
We present a thorough discussion of light dark matter produced via freeze-in in two-body decays A -> B DM. If A and B are quasi-degenerate, the dark matter particle has a cold spectrum even for keV masses. We show this explicitly by calculating the transfer function that encodes the impact on structure formation. As examples for this setup we study extended seesaw mechanisms with a spontaneously broken global U(1) symmetry, such as the inverse seesaw. The keV-scale pseudo-Goldstone dark matter particle is then naturally produced cold by the decays of the quasi-degenerate right-handed neutrinos.
... Tremaine-Gunn bound The mass of the sterile neutrinos is also restricted by an absolute lower limit, the so-called Tremaine-Gunn (TG) bound [109], which arises from fermions having a maximal phase space density. When applied to astrophysical ob-jects such as the central regions of galaxies, the resulting mass turns out to be m N 0.5 keV [25]. ...
Preprint
We investigate the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars. All previous studies applied simplifying assumptions and/or studied the process only on the level of number densities, which makes it impossible to give statements about cosmic structure formation. We overcome these issues by dropping all simplifying assumptions (except for one we showed earlier to work perfectly) and by computing the full course of Dark Matter production on the level of non-thermal momentum distribution functions. We are thus in the position to study all aspects of the resulting settings and apply all relevant bounds in a reliable manner. We have a particular focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free-streaming horizon clearly fails for highly non-thermal distributions. Our work comprises the most detailed and comprehensive study of sterile neutrino Dark Matter production by scalar decays presented so far.
... In reality, we expect the neutrinos to start falling into the potential wells of the cold matter once they become non-relativistic and to eventually form neutrino haloes around those of CDM (e.g., Ringwald & Wong 2004;Abazajian et al. 2005); but this is ignored in our modelling. Note that the conservation of the neutrino phase-space density prevents these neutrino haloes from becoming as dense as their CDM counterparts (Tremaine & Gunn 1979). Table 5 Both 'all matter' and baryon densities are held fixed as the neutrino mass is varied, so increasing m ν consequently decreases Ω c . ...
Preprint
We present an accurate non-linear matter power spectrum prediction scheme for a variety of extensions to the standard cosmological paradigm, which uses the tuned halo model previously developed in Mead (2015b). We consider dark energy models that are both minimally and non-minimally coupled, massive neutrinos and modified gravitational forces with chameleon and Vainshtein screening mechanisms. In all cases we compare halo-model power spectra to measurements from high-resolution simulations. We show that the tuned halo model method can predict the non-linear matter power spectrum measured from simulations of parameterised w(a) dark energy models at the few per cent level for k<10hMpc1k<10\,h\mathrm{Mpc}^{-1}, and we present theoretically motivated extensions to cover non-minimally coupled scalar fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k<10hMpc1k<10\,h\mathrm{Mpc}^{-1}. For chameleon screened models we achieve only 10 per cent accuracy for the same range of scales. Finally, we use our halo model to investigate degeneracies between different extensions to the standard cosmological model, finding that the impact of baryonic feedback on the non-linear matter power spectrum can be considered independently of modified gravity or massive neutrino extensions. In contrast, considering the impact of modified gravity and massive neutrinos independently results in biased estimates of power at the level of 5 per cent at scales k>0.5hMpc1k>0.5\,h\mathrm{Mpc}^{-1}. An updated version of our publicly available HMcode can be found at https://github.com/alexander-mead/HMcode
... The range of viable DM masses is restricted to 0.1 keV m DM 50 keV. Smaller masses are forbidden by the Tremaine-Gunn bound [129] (derived by comparing the observed size of dwarf galaxies with a Fermi sphere of DM fermions, see also [130][131][132]) while above 50 keV, the DM candidate is no longer cosmologically stable. Taking into account additional observational constraints on the active sterile mixing, the DW mechanism can account for about 30% of the total dark matter density today [22]. ...
Preprint
We consider the possibility of simultaneously addressing the baryon asymmetry of the Universe, the dark matter problem and the neutrino mass generation in minimal extensions of the Standard Model via sterile fermions with (small) total lepton number violation. Within the framework of Inverse and Linear Seesaw models, the small lepton number violating parameters set the mass scale of the active neutrinos, the efficiency of leptogenesis through a small mass splitting between pairs of sterile fermions as well as the mass scale of a sterile neutrino dark matter candidate. We provide an improved parametrization of these seesaw models taking into account existing experimental constraints and derive a linearized system of Boltzmann equations to describe the leptogenesis process, which allows for an efficient investigation of the parameter space. This in particular enables us to perform a systematic study of the strong washout regime of leptogenesis. Our study reveals that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between two sterile states with a natural origin of the (necessary) strong degeneracy in their mass spectrum. The minimal model however requires a non-standard cosmological history to account for the relic dark matter. Finally, we discuss the prospect for neutrinoless double beta decay and for testing, in future experiments, the values of mass and different active-sterile mixings required for successful leptogenesis.
... This argument is similar to the reasoning underlying the Tremaine-Gunn bound (Tremaine & Gunn 1979), in which the authors used an isothermal profile in the Milky Way galaxy and other structures to put a lower mass bound on dark matter based solely on phase space density considerations, and a slightly weaker bound based on Fermi repulsion. They too obtained their bound by observing that with too small a mass for the dark matter particle, objects of a given total mass would exceed their observed sizes (this statement can be re-expressed in terms of velocity dispersions). ...
Preprint
We show that Fermi repulsion can lead to cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. We treat the dark matter as a quasi-degenerate self-gravitating Fermi gas and calculate its density profile assuming hydrostatic equilibrium. We find that suitable dwarf galaxy cores of larger than 130 pc can be achieved for fermion dark matter with mass in the range 70 eV - 400 eV. While in conventional dark matter scenarios, such sub-keV thermal dark matter would be excluded by free streaming bounds, the constraints are ameliorated in models with dark matter at lower temperature than conventional thermal scenarios, such as the Flooded Dark Matter model that we have previously considered. Modifying the arguments of Tremaine and Gunn we derive a conservative lower bound on the mass of fermionic dark matter of 70 eV and a stronger lower bound from Lyman-α\alpha clouds of about 470 eV, leading to slightly smaller cores than have been observed. We comment on this result and how the tension is relaxed in dark matter scenarios with non-thermal momentum distributions.
... On the other hand, velocity dispersion (e.g. Tremaine & Gunn 1979;Melott 1983;Teles et al. 2011;Joyce & Worrakitpoonpon 2011;Colombi & Touma 2014) also leads to the development of a central core, often attributed to the fact that, according to Liouville's theorem, the fine-grained distribution function in phase space cannot increase, and therefore the finite initial value places a strong upper limit at any later time. This is extremely relevant for our box case, and Teles et al. (2011) proposed a theoretically-motivated ansatz for the analytical form of the quasi-stationary f ( ) consisting on a central value f0 up to some 'Fermi level' 0 delimiting the core and another constant value f h < f0 up to the maximum energy h attained by the particles in the outer, diffuse halo. ...
Preprint
This work discusses the main analogies and differences between the deterministic approach underlying most cosmological N-body simulations and the probabilistic interpretation of the problem that is often considered in mathematics and statistical mechanics. In practice, we advocate for averaging over an ensemble of S independent simulations with N particles each in order to study the evolution of the one-point probability density Ψ\Psi of finding a particle at a given location of phase space (x,v)(\mathbf{x},\mathbf{v}) at time t. The proposed approach is extremely efficient from a computational point of view, with modest CPU and memory requirements, and it provides an alternative to traditional N-body simulations when the goal is to study the average properties of N-body systems, at the cost of abandoning the notion of well-defined trajectories for each individual particle. In one spatial dimension, our results, fully consistent with those previously reported in the literature for the standard deterministic formulation of the problem, highlight the differences between the evolution of the one-point probability density Ψ(x,v,t)\Psi(x,v,t) and the predictions of the collisionless Boltzmann (Vlasov-Poisson) equation, as well as the relatively subtle dependence on the actual finite number N of particles in the system. We argue that understanding this dependence with N may actually shed more light on the dynamics of real astrophysical systems than the limit NN\to\infty.
... The bound becomes weaker if the dark sector is colder than the SM, as shown in the left panel of Fig. 11, and we find viable sterile coannihilation models with the DM as light as m χ ≈ 5 keV. We find that the constraint from Lyman-α is stronger than the Tremaine-Gunn bound [146], which sets a lower limit on the mass of fermionic DM of several hundred eV [147]. ...
Preprint
Dark matter may be a thermal relic whose abundance is set by mutual annihilations among multiple species. Traditionally, this coannihilation scenario has been applied to weak scale dark matter that is highly degenerate with other states. We show that coannihilation among states with split masses points to dark matter that is exponentially lighter than the weak scale, down to the keV scale. We highlight the regime where dark matter does not participate in the annihilations that dilute its number density. In this "sterile coannihilation" limit, the dark matter relic density is independent of its couplings, implying a broad parameter space of thermal relic targets for future experiments. Light dark matter from coannihilation evades stringent bounds from the cosmic microwave background, but will be tested by future direct detection, fixed target, and long-lived particle experiments.
... These results are obtained on a 100 × 100 grid within the paramter space, which allows the smooth features within the results to be observed. We do not consider m νs ≤ 1.7 keV since they are robustly bound by phase-space constraints [52][53][54]. ...
Preprint
We perform an exhaustive scan of the allowed resonant production regime for sterile neutrino dark matter in order to improve constraints for dark matter structures which arise from the non-thermal sterile neutrino energy spectra. Small-scale structure constraints are particularly sensitive to large lepton asymmetries/small mixing angles which result in relatively warmer sterile neutrino momentum distributions. We revisit Milky Way galaxy subhalo count constraints and combine them with recent searches for X-ray emission from sterile neutrino decays. Together they rule out models outside the mass range 7.0 keV < m_nu_s < 36 keV and lepton asymmetries smaller than 15 x 10-6 per unit entropy density at 95 percent CI or greater. We also find that while a portion of the parameter space remains unconstrained, the combination of subhalo counts and X-ray data indicate the candidate 3.55 keV X-ray line signal potentially originating from a 7.1 keV sterile neutrino decay to be disfavored at 93 percent CI.
... where the dark matter is assumed to be a boson (real scalar), because a fermionic dark matter cannot be an ultralight dark matter due to the Tremaine-Gunn bound [12]. We impose a Z 2 symmetry not to have a less-dimensional interaction, φN N , because it induces a long-range force between a pair of nucleons and already severely constrained [13]. ...
Preprint
A novel idea of the direct detection to search for a ultralight dark matter based on the interaction between the dark matter and a nucleon is proposed. Solar system bodies feel the dark matter wind and it acts as a resistant force opposing their motions. The astronomical ephemeris of solar system bodies is so precise that it has a strong capability to detect a dark matter whose mass is much lighter than O(1) eV. We have estimated the resistant force based on the calculation of the elastic scattering cross section between the dark matter and the bodies beyond the Born approximation, and show that the astronomical ephemeris indeed put a very strong constraint on the interaction between the dark matter and a nucleon, depending on how smoothly the ultralight dark matter is distributed at the scale smaller than the celestial bodies in our solar system.
... One popular class here are models with DM particles around the keV scale. For fermion DM, keV corresponds to the smallest mass that still allows to form the small structures that we observe in our Universe; this Tremaine-Gunn bound [1,2] follows from Fermi-Dirac statistics and holds independently of the DM production mechanism. No such strict lower bound exists for bosonic DM, with many models going far below the keV scale, most prominently discussed for axion DM [3]. ...
Preprint
We explore ways of creating cold keV-scale dark matter by means of decays and scatterings. The main observation is that certain thermal freeze-in processes can lead to a cold dark matter distribution in regions with small available phase space. In this way the free-streaming length of keV particles can be suppressed without decoupling them too much from the Standard Model. In all cases, dark matter needs to be produced together with a heavy particle that carries away most of the initial momentum. For decays, this simply requires an off-diagonal DM coupling to two heavy particles; for scatterings, the coupling of soft DM to two heavy particles needs to be diagonal, in particular in spin space. Decays can thus lead to cold light DM of any spin, while scatterings only work for bosons with specific couplings. We explore a number of simple models and also comment on the connection to the tentative 3.5 keV line.
... There are two main obstacles to detecting DM down to mass scales as light as the warm DM limit (corresponding to m X ∼ 1 keV [20][21][22]). The first is that the initial kinetic energy available for scattering, E i = 1 2 m X v 2 X , becomes as small as 1 meV for keV-mass DM, with the velocity set by the local velocity dispersion of the Milky Way, v X ∼ 10 −3 . ...
Preprint
We show that a two-excitation process in superfluid helium, combined with sensitivity to meV energy depositions, can probe dark matter down to the ~keV warm dark matter mass limit. This mass reach is three orders of magnitude below what can be probed with ordinary nuclear recoils in helium at the same energy resolution. For dark matter lighter than 100\sim 100 keV, the kinematics of the process requires the two athermal excitations to have nearly equal and opposite momentum, potentially providing a built-in coincidence mechanism for controlling backgrounds.
... When m X mX , this constraint also applies to the dipole transition given by Eq. (15), implying Λ 400 GeV. Although this bound is consistent with Eq. (10) for small DM masses, imposing the Tremaine-Gunn bound m X f −1/4 X ≥ 0.5 keV [59,60] rules out the possibility of fermionic DM. Since the effective temperature scales as f X , cases where only a fraction f X < 1 of DM is in the form of excited DM are also excluded. ...
Preprint
The recently claimed anomaly in the measurement of the 21 cm hydrogen absorption signal by EDGES at z17z\sim 17, if cosmological, requires the existence of new physics. The possible attempts to resolve the anomaly rely on either (i) cooling the hydrogen gas via new dark matter-hydrogen interactions or (ii) modifying the soft photon background beyond the standard CMB one, as possibly suggested also by the ARCADE~2 excess. We argue that solutions belonging to the first class are generally in tension with cosmological dark matter probes once simple dark sector models are considered. Therefore, we propose soft photon emission by light dark matter as a natural solution to the 21 cm anomaly, studying a few realizations of this scenario. We find that the signal singles out a photophilic dark matter candidate characterised by an enhanced collective decay mechanism, such as axion mini-clusters.
... The dashed red line extrapolates the latter constraint to m s > 10 keV. Other regions of parameter space are excluded by the Tremaine-Gunn condition on the kinetic stability of dwarf galaxies (m s < 0.5 keV is excluded) [59], the diffuse X-ray background [60], the observed flux of X-rays from Andromeda [61] and the Milk Way [62,63], and a Lyman-α limit on the suppression of small scale structure for non-resonant production based on the bounds from [64] and the conversion formula from [65]. The latter limit is only valid for the Dodelson-Widrow (DW) non-resonant freeze-in model [58], which is depicted by the black line. ...
Preprint
Cosmic reionization and dark matter decay can impact observations of the cosmic microwave sky in a similar way. A simultaneous study of both effects is required to constrain unstable dark matter from cosmic microwave background observations. We compare two reionization models with and without dark matter decay. We find that a reionization model that fits also data from quasars and star forming galaxies results in tighter constraints on the reionization optical depth τreio\tau_{\text{reio}}, but weaker constraints on the spectral index nsn_{\text{s}} than the conventional parametrization. We use the Planck 2015 data to constrain the effective decay rate of dark matter to Γeff<2.9×1025/\Gamma_{\rm eff} < 2.9 \times 10^{-25}/s at 95\% C.L. This limit is robust and model independent. It holds for any type of decaying dark matter and it depends only weakly on the chosen parametrization of astrophysical reionization. For light dark matter particles that decay exclusively into electromagnetic components this implies a limit of Γ<5.3×1026/\Gamma < 5.3 \times 10^{-26}/s at 95\% C.L. Specifying the decay channels, we apply our result to the case of keV-mass sterile neutrinos as dark matter candidates and obtain constraints on their mixing angle and mass, which are comparable to the ones from the diffuse X-ray background.
... The possibility to constrain the DM particle mass by determining the DM phase space distribution was first considered in the seminal work by Tremaine & Gunn (1979). In the hypothesis of non-dissipative evolution, i.e. conservation of the maximal phase space density, it is possible to set a strong bounds on the DM mass m >300-700 eV, see e.g. ...
Preprint
We reconsider the lower bound on the mass of a fermionic dark matter (DM) candidate resulting from the existence of known small Dwarf Spheroidal galaxies, in the hypothesis that their DM halo is constituted by degenerate fermions, with phase-space density limited by the Pauli exclusion principle. By relaxing the common assumption that the DM halo scale radius is tied to that of the luminous stellar component and by marginalizing on the unknown stellar velocity dispersion anisotropy, we prove that observations lead to rather weak constraints on the DM mass, that could be as low as tens of eV. In this scenario, however, the DM halos would be quite large and massive, so that a bound stems from the requirement that the time of orbital decay due to dynamical friction in the hosting Milky Way DM halo is longer than their lifetime. The smallest and nearest satellites Segue I and Willman I lead to a final lower bound of m100m\gtrsim100 eV, still weaker than previous estimates but robust and independent on the model of DM formation and decoupling. We thus show that phase space constraints do not rule out the possibility of sub-keV fermionic DM.
... WDM halos do not suffer from the TBTF prob-lem to the same degree as they form later with a reduced central density than CDM halos of similar masses (Lovell et al. 2012;Horiuchi et al. 2016;Lovell et al. 2017a). WDM halos can also feature cored dark matter density profiles (Tremaine & Gunn 1979;Dalcanton & Hogan 2001), but the free-streaming scales of the models we consider here are not expected to resolve the cusp-core problem (Villaescusa-Navarro & Dalal 2011;Macciò et al. 2012). For example, a thermal WDM particle with mass, m thm = 2 keV is predicted to produce a r ≈ 10 pc core in a 10 10 M halo, which falls significantly below the ∼ 100 − 1000 pc core size observationally inferred for dwarf galaxies (Gilmore et al. 2007;Walker & Peñarrubia 2011;Oh et al. 2011). ...
Preprint
We study the impact of a warm dark matter (WDM) cosmology on dwarf galaxy formation through a suite of cosmological hydrodynamical zoom-in simulations of Mhalo1010MM_{\rm halo} \approx10^{10}\,M_{\odot} dark matter halos as part of the Feedback in Realistic Environments (FIRE) project. A main focus of this paper is to evaluate the combined effects of dark matter physics and stellar feedback on the well-known small-scale issues found in cold dark matter (CDM) models. We find that the z=0 stellar mass of a galaxy is strongly correlated with the central density of its host dark matter halo at the time of formation, zfz_{\rm f}, in both CDM and WDM models. WDM halos follow the same M(z=0)Vmax(zf)M_{\star}(z=0)-V_{\rm max}(z_{\rm f}) relation as in CDM, but they form later, are less centrally dense, and therefore contain galaxies that are less massive than their CDM counterparts. As a result, the impact of baryonic effects on the central gravitational potential is typically diminished relative to CDM. However, the combination of delayed formation in WDM and energy input from stellar feedback results in dark matter profiles with lower overall densities. The WDM galaxies studied here have a wider diversity of star formation histories (SFHs) than the same systems simulated in CDM, and the two lowest MM_{\star} WDM galaxies form all of their stars at late times. The discovery of young ultra-faint dwarf galaxies with no ancient star formation -- which do not exist in our CDM simulations -- would therefore provide evidence in support of WDM.
... For fermionic dark matter, which we consider in this work, masses below roughly 100 keV are excluded based on the phase space of the dark matter within galaxies, as famously pointed out in Ref. [78]. In each of our result plots (both for electrons, and below for protons), we show an updated version of this bound taken from Ref. [77], which rules out the low-mass end of the parameter space we show. ...
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Cosmic ray (CR) upscattering of dark matter is considered as one of the most straightforward mechanisms to accelerate ambient dark matter, making it detectable at high threshold, large volume experiments. In this work, we revisit CR upscattered dark matter signals at the IceCube detector, focusing on lower energy data than was considered before. We consider both scattering with electrons and nuclei. In the latter, we include both elastic and deep-inelastic scattering computations. As concrete examples, we consider two benchmark models; fermion dark matter with vector and scalar mediators. We compare our model projections with the most current constraints and show that the IceCube detector can detect CR-boosted dark matter especially with masses below ∼ 100 keV when scattering with electrons and ∼ MeV in the nucleon scattering case. Published by the American Physical Society 2024
... therefore the number density of fermionic DM in a galaxy is bounded as well (recalling This is known as the Tremaine-Gunn limit [32]. For bosonic DM, there is a lower bound on ultra-light particles. ...
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In this thesis, we present a comprehensive and pedagogical overview of dark matter (DM). Chapter 1 discusses the main evidences for its existence, its properties, and potential candidates. We then explore major detection strategies, with Chapter 2 specifically dedicated to indirect detection. In the following chapters, we study the emission of secondary photons resulting from the interaction between DM products and the Galactic environment. Chapters 3 and 4 focus on DM as sub-GeV particles, analysing how the DM-produced electrons and positrons interact with ambient photons to generate X-rays through inverse Compton scattering. Comparing the predicted spectra with data from X-ray observatories yields strong constraints on sub-GeV DM. Chapter 5 extends these techniques to the case of primordial black hole (PBH) evaporation, imposing significant limits on PBHs as potential DM candidates.
... Also due to such low DM mass, the decay width of ϕ is small (∝ m 2 χ ), resulting in ϕ decaying very close to the BBN era. This brings two major problems, namely, (i) the late decay of ϕ leads to a large free-streaming length of DM (as shown in [84,85]), potentially giving hot DM that is already ruled out from structure formation constraint; (ii) DM mass range lies in the boundary of the Tremaine-Gunn bound for fermionic dark matter [86]. These problems get worse for a higher v Φ , making the scenario m ϕ < 2m N for λ ϕ ¼ 10 −3 disfavored. ...
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We study the possibility of testing a dark matter (DM) scenario embedded in a global lepton number symmetry U ( 1 ) L via gravitational waves (GWs) and cosmic microwave background (CMB) observations. The spontaneous breaking of U ( 1 ) L symmetry generates the seesaw scale as well as DM mass dynamically. The (pseudo-)Nambu-Goldstone boson, known as a Majoron, acquires nonzero mass due to soft symmetry-breaking terms of quadratic type in the scalar potential, which eventually breaks U ( 1 ) L to its Z 2 subgroup. The spontaneous symmetry breaking, which effectively breaks Z 2 , leads to the formation of domain walls (DWs), posing a threat to successful cosmology, if allowed to dominate. As gravity does not respect any global symmetries, we consider higher-dimensional operators suppressed by the scale of quantum gravity (QG), namely, Λ QG , which introduces the required bias leading to DW annihilation and emission of stochastic GWs observable at near future experiments. The same operators also lead to decay of DM bringing interesting indirect detection aspects. While DM is produced nonthermally via scalar portal interactions, light Majorons can give rise to additional Δ N eff within reach of future CMB experiments. Published by the American Physical Society 2024
... These phonons could be detected in planned experiments based on single-phonon sensing (e.g., TESSERACT [50]) with energy thresholds of O(meV) ( corresponding to O(THz) frequency thresholds). Achieving an O(meV) energy threshold would allow sensitivity down to m DM > ∼ keV via a scattering event (an important milestone since m DM ∼ keV is the lightest fermionic DM is allowed to be [51]), and m DM > ∼ meV via an absorption event. Many of the detector technologies aiming to reach such thresholds rely on superconducting "pairbreaking" sensors such as transition edge sensors, kinetic inductance detectors, superconducting qubits, and quantum capacitance detectors [52][53][54][55][56][57][58][59][60][61]. ...
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We present a novel application of a qubit-coupled phonon detector to search for new physics, e.g., ultralight dark matter (DM) and high-frequency gravitational waves. The detector, motivated by recent advances in quantum acoustics, is composed of superconducting transmon qubits coupled to high-overtone bulk acoustic resonators (hBARs) and operates in the GHz - 10 GHz frequency range. New physics can excite O(10μeV)O(10 \, \mu \text{eV}) phonons within the hBAR, which are then converted to qubit excitations via a transducer. We detail the design, operation, backgrounds, and expected sensitivity of a prototype detector, as well as a next-generation detector optimized for new physics signals. We find that a future detector can complement current haloscope experiments in the search for both dark photon DM and high-frequency gravitational waves. Lastly we comment on such a detector's ability to operate as a 10μeV10 \, \mu\text{eV} threshold athermal phonon sensor for sub-GeV DM detection.
... The canonical example, a weakly interacting massive particle (WIMP) [1], sets specific experimental targets by determining the dark matter relic abundance via its interaction strength with SM particles through thermal freeze-out [4][5][6]. Dark matter as a thermal relic would be too warm at late times if its mass were below ∼ keV [7][8][9][10][11][12][13][14]; in this mass range, the dark matter must also be bosonic [15][16][17][18][19][20][21][22][23][24][25][26][27]. Axions and dark photons dominate theoretical and experimental efforts in this ultralight regime, since symmetries can protect their masses from large quantum corrections. ...
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Ultralight dark photon dark matter features distinctive cosmological and astrophysical signatures and is also supported by a burgeoning direct-detection program searching for its kinetic mixing with the ordinary photon over a wide mass range. Dark photons, however, cannot necessarily constitute the dark matter in all of this parameter space. In minimal models where the dark photon mass arises from a dark Higgs mechanism, early Universe dynamics can easily breach the regime of validity of the low-energy effective theory for a massive vector field. In the process, the dark sector can collapse into a cosmic string network, precluding dark photons as viable dark matter. We establish the general conditions under which dark photon production avoids significant backreaction on the dark Higgs and identify regions of parameter space that naturally circumvent these constraints. After surveying implications for known dark photon production mechanisms, we propose novel models that set well-motivated experimental targets across much of the accessible parameter space. We also discuss complementary cosmological and astrophysical signatures that can probe the dark sector physics responsible for dark photon production.
... Assuming the sensitivity of future torsion balance experiments increases by two orders, the constraints will also strengthen by two orders, as indicated by the green dashed line. Interestingly, the region IV is extended into the light fermion mass region, (0.1, 1) keV [50,51], though the coherent effect starts decreasing, giving σ χN ≲ (10 −40 , 10 −38 ) cm 2 . This is stronger than the constraints from the direct detection of such fermion DMs [40,52,53]. ...
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Dark matter with mass in the crossover range between wave dark matter and particle dark matter, around (103,103)(10^{-3},\, 10^3)\,eV, remains relatively unexplored by terrestrial experiments. In this mass regime, dark matter scatters coherently with macroscopic objects. The effect of the coherent scattering greatly enhances the accelerations of the targets that the dark matter collisions cause by a factor of 1023\sim 10^{23}. We propose a novel torsion balance experiment with test bodies of different geometric sizes to detect such dark matter-induced acceleration. This method provides the strongest constraints on the scattering cross-section between the dark matter and a nucleon in the mass range (105,103)(10^{-5}, 10^3)\,eV.
... Additionally, a lower limit on the mass of fermionic dark matter m DM;f տ 100 eV is imposed by the Tremaine-Gunn bound. 27 Motivated by the expected experimental signal and for ease of discussion, we will split the particulate candidates broadly into two categories. If the number density is sufficiently high (occurring for bosonic dark matter masses m v Շ 1 eV), then the field can be approximately described by a Bose-Einstein condensate, exhibiting wave-like behavior and coherence over a timescale set by the natural frequency of the field. ...
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Motivated by the current interest in employing quantum sensors on Earth and in space to conduct searches for new physics, we provide a perspective on the suitability of large-mass levitated optomechanical systems for observing dark matter signatures. We discuss conservative approaches of recoil detection through spectral analysis of coherently scattered light, enhancements of directional effects due to cross-correlation spectral densities, and the possibility of using quantum superpositions of mesoscopic test particles to measure rare events.
... The effect of WDM that we consider is the suppression in the number density of low mass halos. Besides this effect, WDM predicts the existence of finite central cores in DM halos [18,71], as opposed to the cuspy profile expected in CDM. The presence of a central core reduces the Einstein angle of the lens, resulting in smaller time delays as compared to halos without core. ...
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Next-generation ground-based gravitational-wave (GW) detectors are expected to detect millions of binary black hole mergers during their operation period. A small fraction (0.11%\sim 0.1 - 1\%) of them will be strongly lensed by intervening galaxies and clusters, producing multiple copies of the GW signals. The expected number of lensed events and the distribution of the time delay between lensed images will depend on the mass distribution of the lenses at different redshifts. Warm dark matter or fuzzy dark matter models predict lower abundances of small mass dark matter halos as compared to the standard cold dark matter. This will result in a reduction in the number of strongly lensed GW events, especially at small time delays. Using the number of lensed events and the lensing time delay distribution, we can put a lower bound on the mass of the warm/fuzzy dark matter particle from a catalog of lensed GW events. The expected bounds from GW strong lensing from next-generation detectors are significantly better than the current constraints.
... There also exist constraints from Lyman-α [85,86] and Milky Way subhalos [87,88] and satellite galaxies [89], all of which rule out sterile neutrino DM below a few keV. We show here the latest DES bound of 6.5 keV [89], but although stronger than the theoretical Tremaine-Gunn bound obtained from phase-space considerations [90], it depends on the sterile neutrino DM production mechanism [91,92], and can in principle be modified in presence of additional interactions [93,94]; therefore, we do not shade the region labeled 'DES'. For the same reason, we do not show the DM over/underproduction bounds, which very much depend on the specific production mechanism considered [94]. ...
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We study the kinetic cooling (heating) of old neutron stars due to coherent scattering with relic neutrinos (sterile neutrino dark matter) via Standard Model neutral-current interactions. We take into account several important physical effects, such as gravitational clustering, coherent enhancement, neutron degeneracy and Pauli blocking. We find that the anomalous cooling of nearby neutron stars due to relic neutrino scattering might actually be observable by current and future telescopes operating in the optical to near-infrared frequency band, such as the James Webb Space Telescope (JWST), provided there is a large local relic overdensity that is still allowed. Similarly, the anomalous heating of neutron stars due to coherent scattering with keV-scale sterile neutrino dark matter, could also be observed by JWST or future telescopes, which would probe hitherto unexplored parameter space in the sterile neutrino mass-mixing plane.
... In fact, major experimental constraints on active-sterile neutrino mixing primarily come from such x-ray searches [6][7][8][9][10][11]. There are also other significant constraints from phase-space considerations (the Tremaine-Gunn bound) [12][13][14][15], measurement of Lyman-α forests [16][17][18], and terrestrial nuclear decay searches [19][20][21][22]. Among many theoretical explorations, a number of studies have investigated the effects of activesterile neutrino mixing in core-collapse supernovae (CCSNe) [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. ...
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We study ν μ − ν s and ν ¯ μ − ν ¯ s mixing in the protoneutron star (PNS) created in a core-collapse supernova (CCSN). We point out the importance of the feedback on the general composition of the PNS in addition to the obvious feedback on the ν μ lepton number. We show that for our adopted mixing parameters δ m 2 ∼ 10 2 keV 2 and sin 2 2 θ consistent with the current constraints, sterile neutrino production is dominated by the Mikheyev–Smirnov–Wolfenstein conversion of ν ¯ μ into ν ¯ s and that the subsequent escape of ν ¯ s increases the ν μ lepton number, which in turn enhances muonization of the PNS primarily through ν μ + n → p + μ − . While these results are qualitatively robust, their quantitative effects on the dynamics and active neutrino emission of core-collapse supernovae should be evaluated by including ν μ − ν s and ν ¯ μ − ν ¯ s mixing in the simulations. Published by the American Physical Society 2024
... For thermally produced DM, the limit is conventionally drawn down to 1 keV DM mass because the thermally produced fermionic DM of mass less than O(1) keV would be hot (v ≫ 10 −3 c) and cannot be contained within the galactic halo as a structural part of it. The mass of the fermionic DM is additionally constrained to be ≳ O(100) eV by the Pauli exclusion principle [130]; however, the recent study on ultralight fermionic dark matter [131] shows that the constraint can be relaxed by an order of 16. 5 Thus, although for completeness we consider the light DM down to 1 eV, the validity of fermionic DM of mass less than O(1) keV is still debatable. Even if we evade the mass constraint following ref. ...
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