[Show abstract][Hide abstract] ABSTRACT: We reexamine the recently proposed "little inflation" scenario that allows
for a strong first order phase-transition of QCD at non-negligible baryon
number in the early universe and its possible observable consequences. The
scenario is based on the assumptions of a strong mechanism for baryogenesis and
a quasistable QCD-medium state which triggers a short inflationary period of
inflation diluting the baryon asymmetry to the value observed today. The
cosmological implications are reexamined, namely effects on primordial density
fluctuations up to dark matter mass scales of $M_{max} \sim 1 M_{\astrosun}$,
change in the spectral slope up to $M_{max} \sim 10^6 M_{\astrosun}$,
production of seeds for the present galactic and extragalactic magnetic fields
and a gravitational wave spectrum with a peak frequency around $\nu_{peak} \sim
4 \cdot 10^{-8} Hz$. We discuss the issue of nucleation in more detail and
employ a chiral effective model of QCD to study the impact on small scale
structure formation.
[Show abstract][Hide abstract] ABSTRACT: For large baryochemical potential, strongly interacting matter might undergo
a first order phase transition at temperatures T ~ 100-200 MeV. Within standard
cosmology, however, the chemical potential is assumed to be very small leading
to a crossover. We discuss implications of a first order QCD transition at high
chemical potential being consistent with current observations. In this
contribution we concentrate on effects on the gravitational wave spectrum.
There are other interesting cosmological signals as a modification of the power
spectrum of dark matter, the production of stellar black holes, and the seeds
for the extragalactic magnetic fields which we briefly address also.
[Show abstract][Hide abstract] ABSTRACT: We investigate cosmological implications of an energy density contribution
arising by elastic dark matter self-interactions. Its scaling behaviour shows
that it can be the dominant energy contribution in the early universe.
Constraints from primordial nucleosynthesis give an upper limit on the
self-interaction strength which allows for the same strength as standard model
strong interactions. Furthermore we explore the cosmological consequences of an
early self-interaction dominated universe. Chemical dark matter decoupling
requires that self-interacting dark matter particles are rather light (keV
range) but we find that super-weak inelastic interactions are predicted by
strong elastic dark matter self-interactions. Assuming a second, collisionless
cold dark matter component, its natural decoupling scale exceeds the weak scale
and is in accord with the electron and positron excess observed by PAMELA and
Fermi-LAT. Structure formation analysis reveals a linear growing solution
during self-interaction domination, enhancing structures up to ~ 10^(-3) solar
masses long before the formation of the first stars.
[Show abstract][Hide abstract] ABSTRACT: The QCD phase diagram might exhibit a first order phase transition for large
baryochemical potentials. We explore the cosmological implications of such a
QCD phase transition in the early universe. We propose that the large
baryon-asymmetry is diluted by a little inflation where the universe is trapped
in a false vacuum state of QCD. The little inflation is stopped by bubble
nucleation which leads to primordial production of the seeds of extragalactic
magnetic fields, primordial black holes and gravitational waves. In addition
the power spectrum of cold dark matter can be affected up to mass scales of a
billion solar masses. The imprints of the cosmological QCD phase transition on
the gravitational wave background can be explored with the future gravitational
wave detectors LISA and BBO and with pulsar timing.
Progress in Particle and Nuclear Physics 12/2010; 66(2). DOI:10.1016/j.ppnp.2011.01.017 · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have investigated effects of the QCD phase transition on the relic GW
spectrum applying several equations of state for the strongly interacting
matter: Besides the bag model, which describes a first order transition, we use
recent data from lattice calculations featuring a crossover. Finally, we
include a short period of inflation during the transition which allows for a
first order phase transition at finite baryon density. Our results show that
the QCD transition imprints a step into the spectrum of GWs. Within the first
two scenarios, entropy conservation leads to a step-size determined by the
relativistic degrees of freedom before and after the transition. The inflation
of the third scenario much stronger attenuates the high-frequency modes: An
inflationary model being consistent with observation entails suppression of the
spectral energy density by a factor of ~10^(-12).
[Show abstract][Hide abstract] ABSTRACT: We explore a scenario that allows for a strong first order phase transition of QCD at a non-negligible baryon number in the early Universe and its possible observable consequences. The main assumption is a quasistable QCD-vacuum state that leads to a short period of inflation, consequently diluting the net baryon to photon ratio to today's observed value. A strong mechanism for baryogenesis is needed to start out with a baryon asymmetry of order unity, e.g., as provided by Affleck-Dine baryogenesis. The cosmological implications are direct effects on primordial density fluctuations up to dark matter mass scales of M{max}∼1-10M{⊙}, change in the spectral slope up to M{max}∼10{6}-10{8}M{⊙}, production of strong primordial magnetic fields and a gravitational wave spectrum with present day peak strain amplitude of up to h{c}(ν{peak})∼5×10{-15} around ν{peak}∼4×10{-8} Hz.
[Show abstract][Hide abstract] ABSTRACT: We investigate cosmological constraints on an energy density contribution of elastic dark matter self-interactions characterized by the mass of the exchange particle and coupling constant. Because of the expansion behaviour in a Robertson-Walker metric we investigate self-interacting dark matter that is warm in the case of thermal relics. The scaling behaviour of dark matter self-interaction energy density shows that it can be the dominant contribution (only) in the very early universe. Thus its impact on primordial nucleosynthesis is used to restrict the interaction strength, which we find to be at least as strong as the strong interaction. Furthermore we explore dark matter decoupling in a self-interaction dominated universe, which is done for the self-interacting warm dark matter as well as for collisionless cold dark matter in a two component scenario. We find that strong dark matter self-interactions do not contradict super-weak inelastic interactions between self-interacting dark matter and baryonic matter and that the natural scale of collisionless cold dark matter decoupling exceeds the weak scale and depends linearly on the particle mass. Finally structure formation analysis reveals a linear growing solution during self-interaction domination; however, only non-cosmological scales are enhanced. Comment: 14 pages, 14 figures; version published in Phys. Rev. D
[Show abstract][Hide abstract] ABSTRACT: Some recent developments concerning the role of strange quark matter for astrophysical systems and the QCD phase transition in the early universe are addressed. Causality constraints of the soft nuclear equation of state as extracted from subthreshold kaon production in heavy-ion collisions are used to derive an upper mass limit for compact stars. The interplay between the viscosity of strange quark matter and the gravitational wave emission from rotation-powered pulsars are outlined. The flux of strange quark matter nuggets in cosmic rays is put in perspective with a detailed numerical investigation of the merger of two strange stars. Finally, we discuss a novel scenario for the QCD phase transition in the early universe, which allows for a small inflationary period due to a pronounced first order phase transition at large baryochemical potential. Comment: 8 pages, invited talk given at the International Conference on Strangeness in Quark Matter (SQM2009), Buzios, Brasil, September 28 - October 2, 2009
Journal of Physics G Nuclear and Particle Physics 02/2010; DOI:10.1088/0954-3899/37/9/094005 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We explore a model for a fermionic dark matter particle family which decouples from the rest of the partices when at least all standard model particles are in equilibrium. We calculate the allowed ranges for mass and chemical potential to be compatible with big bang nucleosynthesis (BBN) calculations and WMAP-data for a flat universe with dark energy. Futhermore we estimate the free streaming length for fermions and antifermions to allow comparison to large scale structure data (LLS). We find that for dark matter decoupling when all standard model particles are present even the least restrictive combined BBN calculation and WMAP results allow us to constrain the initial dark matter chemical potential to a highest value of 6.3 times the dark matter temperature. In this case the resulting mass range is at most 1.8 eV < m < 53 eV, where the upper bound scales linearly with the effective degrees of freedom at decoupling. From LSS we find that similar to ordinary warm dark matter models the particle mass has to be larger than approximately 500 eV (meaning the effective degrees of freedom at decoupling have to be > 1000) to be compatible with observations of the Ly alpha forest at high redshift, but still the dark matter chemical potential over temperature ratio can exceed unity.
[Show abstract][Hide abstract] ABSTRACT: In standard cosmology, one concludes that the early universe evolves along µ B ∼ 0. Thus, the early universe would cross the QCD phase transition where one expects a crossover transi-tion from lattice gauge calculations. Fig. 1: Evolution through the QCD phase diagram in the standard cosmological scenario: The universe passes through the crossover region of the QCD phase diagram at µ/T ∼ 0. Evolution through the QCD phase diagram for the little inflation scenario: The universe is trapped in a metastable vacuum at the first order phase transition line, supercools and is reheated back close to the critical temperature. A first order phase transition allows for a false metastable vac-uum state where the universe could be trapped for some time → Inflationary Phase. The baryon to photon ratios before and after the inflationary period should scale with the ratio of the scale parameters cubed as entropy is produced during reheating while baryon number is conserved so that µ B T f ≈ a i a f 3 µ B T i . The final ratio should be 10 −9 as observed. So we need just a boost of N = ln (a f /a i) ∼ ln(10 3) ∼ 7, i.e. seven e-folds, to get an initial ratio of (µ B /T) i ∼ O(1). Our scenario [1] is as follows: • The early universe is at large baryochemical potentials µ B /T 1 initially. • The early universe reaches the first order phase transi-tion line of QCD at high baryochemical potentials and is trapped in the false vacuum. The inflationary period starts with supercooling and dilu-tion with µ B /T = const. • The decay to the true vacuum state will release latent heat, so that the universe is reheated to T ∼ T c . Due to the entropy produced during the transition the final baryon to photon ratio is given by µ B /T ∼ 10 −9 . • Finally, the universe evolves along the standard cosmolog-ical path. The path through the QCD phase diagram for the little inflation scenario is depicted in Fig. 1.