Georg G. Raffelt

Max Planck Institute of Physics, München, Bavaria, Germany

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Publications (298)1068.66 Total impact

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    A. Kartavtsev, G. Raffelt, H. Vogel
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    ABSTRACT: Neutrinos propagating in media (matter and electromagnetic fields) undergo flavor and helicity oscillations, where helicity transitions are instigated both by electromagnetic fields and matter currents. In addition, it has been shown that correlations between neutrinos and antineutrinos of opposite momentum can build up in anisotropic media. We re-derive the neutrino equations of motion in the mean-field approximation for homogeneous yet anisotropic media, confirming previous results except for a small correction in the Majorana case. Furthermore, we derive the mean-field Hamiltonian induced by neutrino electromagnetic interactions. We also provide a phenomenological discussion of pair correlations in comparison with helicity correlations.
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    ABSTRACT: The propagation of TeV gamma rays can be strongly modified by B-field induced conversion to axionlike particles (ALPs). We show that, at such high energies, photon dispersion is dominated by background photons - the only example where photon-photon dispersion is of practical relevance. We determine the refractive index for all energies and find that, for fixed energy density, background photons below the pair-production threshold dominate. The cosmic microwave background alone provides an "effective photon mass" of (m_gamma)^2 = -(1.01 neV * E/TeV)^2 for E < 1000 TeV. The extragalactic background light is subdominant, but local radiation fields in the galaxy or the source regions provide significant contributions. Photon-photon dispersion is small enough to leave typical scenarios of photon-ALP oscillations unscathed, but big enough to worry about it case by case.
    Physical Review D 04/2015; 91(8). DOI:10.1103/PhysRevD.91.083003 · 4.86 Impact Factor
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    ABSTRACT: In this work we present a search for (solar) chameleons with the CERN Axion Solar Telescope (CAST). This novel experimental technique, in the field of dark energy research, exploits both the chameleon coupling to matter ($\beta_{\rm m}$) and to photons ($\beta_{\gamma}$) via the Primakoff effect. By reducing the X-ray detection energy threshold used for axions from 1$\,$keV to 400$\,$eV CAST became sensitive to the converted solar chameleon spectrum which peaks around 600$\,$eV. Even though we have not observed any excess above background, we can provide a 95% C.L. limit for the coupling strength of chameleons to photons of $\beta_{\gamma}\!\lesssim\!10^{11}$ for $1<\beta_{\rm m}<10^6$.
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    ABSTRACT: We study the potential of a future, large-volume photometric survey to constrain the axion mass $m_a$ in the hot dark matter limit. Future surveys such as Euclid will have significantly more constraining power than current observations for hot dark matter. Nonetheless, the lowest accessible axion masses are limited by the fact that axions lighter than $\sim 0.15$ eV decouple before the QCD epoch, assumed here to occur at a temperature $T_{\rm QCD} \sim 170$ MeV; this leaves an axion population of such low density that its late-time cosmological impact is negligible. For larger axion masses, $m_a \gtrsim 0.15$ eV, where axions remain in equilibrium until after the QCD phase transition, we find that a Euclid-like survey combined with Planck CMB data can detect $m_a$ at very high significance. Our conclusions are robust against assumptions about prior knowledge of the neutrino mass. Given that the proposed IAXO solar axion search is sensitive to $m_a\lesssim 0.2$ eV, the axion mass range probed by cosmology is nicely complementary.
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    ABSTRACT: The propagation of TeV gamma rays can be strongly modified by B-field induced conversion to axion-like particles. The conversion rate depends on the photon dispersion relation which, at such high energies, is dominated by the B-field itself through the QED photon-photon interaction. However, ambient photons also contribute and the cosmic microwave background (CMB) dominates when B < 3.25 micro-Gauss. We determine the photon-photon refractive index for all energies and find that, in intergalactic space, the CMB dominates for dispersion, whereas for absorption by gamma+gamma->electron+positron it is the extra-galactic background light. Local radiation fields, e.g., the galactic star light, can be more important for dispersion than the CMB.
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    ABSTRACT: During the accretion phase of a core-collapse supernova (SN), the deleptonization flux has recently been found to develop a global dipole pattern (LESA---Lepton Emission Self-sustained Asymmetry). The $\nu_e$ minus $\bar\nu_e$ flux essentially vanishes in one direction, potentially facilitating self-induced flavor conversion. On the other hand, below the stalled shock wave, self-induced flavor conversion is typically suppressed by multi-angle matter effects, preventing any impact of flavor conversion on SN explosion dynamics. In a schematic model of SN neutrino fluxes, we study the impact of modified $\bar\nu_e$-$\nu_e$ flux asymmetries on collective flavor conversion. In the parameter space consisting of matter density and effective neutrino density, the region of instability with regard to self-induced flavor conversion is much larger for a vanishing lepton number flux, yet this modification does not intersect a realistic SN profile. Therefore, it appears that, even in the presence of LESA, self-induced flavor conversion remains suppressed below the shock front.
  • Physical Review Letters 11/2014; 113(23). DOI:10.1103/PhysRevLett.113.239903 · 7.73 Impact Factor
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    ABSTRACT: The radiative decay of sterile neutrinos with typical masses of 10 keV is investigated in the presence of a strong magnetic field and degenerate plasma. Full account is taken of the strongly modified photon dispersion relation relative to vacuum. The limiting cases of relativistic and non-relativistic plasma are analyzed. The decay rate in a strongly magnetized plasma as a function of the electron number density is compared with the un-magnetized case. We find that a strong magnetic field suppresses the catalyzing influence of the plasma on the decay rate.
    Physical Review D 10/2014; 90(11). DOI:10.1103/PhysRevD.90.113015 · 4.86 Impact Factor
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    ABSTRACT: The neutrino emission characteristics of the first full-scale three-dimensional supernova simulations with sophisticated three-flavor neutrino transport for three models with masses 11.2, 20 and 27 M_sun are evaluated in detail. All the studied progenitors show the expected hydrodynamical instabilities in the form of large-scale convective overturn. In addition, the recently identified LESA phenomenon (lepton-number emission self-sustained asymmetry) is generic for all our cases. Pronounced SASI (standing accretion-shock instability) activity appears in the 20 and 27 M_sun cases, partly in the form of a spiral mode, inducing large but direction and flavor-dependent modulations of neutrino emission. These modulations can be clearly identified in the existing IceCube and future Hyper-Kamiokande detectors, depending on distance and detector location relative to the main SASI sloshing direction.
    Physical Review D 05/2014; 90(4). DOI:10.1103/PhysRevD.90.045032 · 4.86 Impact Factor
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    ABSTRACT: The CERN Axion Solar Telescope has finished its search for solar axions with He3 buffer gas, covering the search range 0.64 eV≲ma≲1.17 eV. This closes the gap to the cosmological hot dark matter limit and actually overlaps with it. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of gaγ≲3.3×10-10 GeV-1 at 95% C.L., with the exact value depending on the pressure setting. Future direct solar axion searches will focus on increasing the sensitivity to smaller values of gaγ, for example by the currently discussed next generation helioscope International AXion Observatory.
    Physical Review Letters 03/2014; 112(9):091302. · 7.73 Impact Factor
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    ABSTRACT: During the stalled-shock phase of our 3D hydrodynamical core-collapse simulations with energy-dependent, 3-flavor neutrino transport, the lepton-number flux (nu_e minus anti-nu_e) emerges predominantly in one hemisphere. This novel, spherical-symmetry breaking neutrino-hydrodynamical instability is termed LESA for "Lepton-number Emission Self-sustained Asymmetry." While the individual nu_e and anti-nu_e fluxes show a pronounced dipole pattern, the heavy-flavor neutrino fluxes and the overall luminosity are almost spherically symmetric. LESA seems to develop stochastically from convective fluctuations, it exists for hundreds of milliseconds or more, and it persists during violent shock sloshing associated with the standing accretion shock instability. The nu_e minus anti-nu_e flux asymmetry originates predominantly below the neutrinosphere in a region of pronounced proto-neutron star (PNS) convection, which is stronger in the hemisphere of enhanced lepton-number flux. On this side of the PNS, the mass-accretion rate of lepton-rich matter is larger, amplifying the lepton-emission asymmetry, because the spherical stellar infall deflects on a dipolar deformation of the stalled shock. This deformation persists despite extremely nonstationary convective overturn behind the shock. The increased shock radius in the hemisphere of less mass accretion and minimal lepton-number flux (anti-nu_e flux maximum) is sustained by stronger convection on this side, which is boosted by stronger neutrino heating because the average anti-nu_e energy is higher than the average nu_e energy. While these different elements of the LESA phenomenon form a consistent picture, a full understanding remains elusive at present. There may be important implications for neutrino-flavor oscillations, the neutron-to-proton ratio in the neutrino-heated supernova ejecta, and neutron-star kicks, which remain to be explored.
    The Astrophysical Journal 02/2014; 792(2). DOI:10.1088/0004-637X/792/2/96 · 6.28 Impact Factor
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    ABSTRACT: The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4-5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few $\times 10^{-12}$ GeV$^{-1}$ and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling $g_{ae}$ with sensitivity $-$for the first time$-$ to values of $g_{ae}$ not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into $\sim 0.2$ cm$^2$ spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for $\sim$12 h each day.
    Journal of Instrumentation 01/2014; 9(05). DOI:10.1088/1748-0221/9/05/T05002 · 1.53 Impact Factor
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    ABSTRACT: The red-giant branch (RGB) in globular clusters is extended to larger brightness if the degenerate helium core loses too much energy in "dark channels." Based on a large set of archival observations, we provide high-precision photometry for the Galactic globular cluster M5 (NGC 5904), allowing for a detailed comparison between the observed tip of the RGB with predictions based on contemporary stellar evolution theory. In particular, we derive 95% confidence limits of g_{ae}<4.3×10^{-13} on the axion-electron coupling and μ_{ν}<4.5×10^{-12}μ_{B} (Bohr magneton μ_{B}=e/2m_{e}) on a neutrino dipole moment, based on a detailed analysis of statistical and systematic uncertainties. The cluster distance is the single largest source of uncertainty and can be improved in the future.
    Physical Review Letters 12/2013; 111(23):231301. DOI:10.1103/PhysRevLett.111.231301 · 7.73 Impact Factor
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    ABSTRACT: The International Axion Observatory (IAXO) is a new generation axion helioscope aiming at a sensitivity to the axion-photon coupling of g(alpha gamma) greater than or similar to few x 10(-12) GeV-1, i.e. 1-1.5 orders of magnitude beyond the one achieved by CAST, currently the most sensitive axion helioscope. The main elements of IAXO are an increased magnetic field volume together with extensive use of x-ray focusing optics and low background detectors, innovations already successfully tested in CAST. Additional physics cases of IAXO could include the detection of electron-coupled axions invoked to explain the white dwarf cooling, relic axions, and a large variety of more generic axion-like particles (ALPs) and other novel excitations at the low-energy frontier of elementary particle physics.
    Journal of Physics Conference Series 10/2013; 460(1):012002. DOI:10.1088/1742-6596/460/1/012002
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    ABSTRACT: The first full-scale three-dimensional core-collapse supernova (SN) simulations with sophisticated neutrino transport show pronounced effects of the standing accretion shock instability (SASI) for two high-mass progenitors (20 and 27M_{⊙}). In a low-mass progenitor (11.2M_{⊙}), large-scale convection is the dominant nonradial hydrodynamic instability in the postshock accretion layer. The SASI-associated modulation of the neutrino signal (80 Hz in our two examples) will be clearly detectable in IceCube or the future Hyper-Kamiokande detector, depending on progenitor properties, distance, and observer location relative to the main SASI sloshing direction. The neutrino signal from the next galactic SN can, therefore, diagnose the nature of the hydrodynamic instability.
    Physical Review Letters 09/2013; 111(12):121104. DOI:10.1103/PhysRevLett.111.121104 · 7.73 Impact Factor
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    ABSTRACT: Neutrino-neutrino refraction causes self-induced flavor conversion in dense neutrino fluxes. For the first time, we include the azimuth angle of neutrino propagation as an explicit variable and find a new generic multi-azimuth-angle instability which, for simple spectra, occurs in the normal neutrino mass hierarchy. Matter suppression of this instability in supernovae requires larger densities than the traditional bimodal case. The new instability shows explicitly that solutions of the equations for collective flavor oscillations need not inherit the symmetries of initial or boundary conditions. This change of paradigm requires reconsideration of numerous results in this field.
    Physical Review Letters 08/2013; 111(9):091101. DOI:10.1103/PhysRevLett.111.091101 · 7.73 Impact Factor
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    ABSTRACT: Stellar evolution is modified if energy is lost in a "dark channel" similar to neutrino emission. Comparing modified stellar evolution sequences with observations provides some of the most restrictive limits on axions and other hypothetical low-mass particles and on non-standard neutrino properties. In particular, a putative neutrino magnetic dipole moment mu_nu enhances the plasmon decay process, postpones helium ignition in low-mass stars, and therefore extends the red-giant branch (RGB) in globular clusters (GCs). The brightness of the tip of the RGB (TRGB) remains the most sensitive probe for mu_nu and we revisit this argument from a modern perspective. Based on a large set of archival observations, we provide high-precision photometry for the Galactic GC M5 (NGC5904) and carefully determine its TRGB position. On the theoretical side, we add the extra plasmon decay rate brought about by mu_nu to the Princeton-Goddard-PUC stellar evolution code. Different sources of uncertainty are critically examined. The main source of systematic uncertainty is the bolometric correction and the main statistical uncertainty derives from the distance modulus based on main-sequence fitting. (Other measures of distance, e.g., the brightness of RR Lyrae stars, are influenced by the energy loss that we wish to constrain.) The statistical uncertainty of the TRGB position relative to the brightest RGB star is less important because the RGB is well populated. We infer an absolute I-band brightness of M_I=-4.17+/-0.13 mag for the TRGB compared with the theoretical prediction of -3.99+/-0.07 mag, in reasonable agreement with each other. A significant brightness increase caused by neutrino dipole moments is constrained such that mu_nu<2.6x10^-12mu_B(68% CL), where mu_B is the Bohr magneton, and mu_nu<4.5x10^-12 mu_B(95% CL). In these results, statistical and systematic errors have been combined in quadrature.
    Astronomy and Astrophysics 08/2013; 558. DOI:10.1051/0004-6361/201322004 · 4.48 Impact Factor
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    ABSTRACT: We have carried out crowded-field, point-spread function (PSF) photometry for M5 using the DAOPHOT II/ALLFRAME suite of programs (Stetson 1987PASP...99..191S, 1994PASP..106..250S). The current corpus of observations for M5 consists of 2840 CCD images obtained during 40 observing runs on 12 telescopes over a span of 27 years. (1 data file).
  • Georg Raffelt, David de Sousa Seixas
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    ABSTRACT: We construct a simple example for self-induced flavor conversion in dense neutrino gases showing new solutions that violate the symmetries of initial conditions. Our system consists of two opposite momentum modes 1 and 2, each initially occupied with equal densities of nu_e and anti-nu_e. Restricting solutions to symmetry under 1 <-> 2 allows for the usual bimodal instability ("flavor pendulum") in the inverted neutrino mass hierarchy (IH) and stability (no self-induced flavor conversion) in the normal hierarchy (NH). Lifting this symmetry restriction allows for a second pendulum-like solution that occurs in NH where the modes 1 and 2 swing in opposite directions in flavor space. Any small deviation from 1-2 symmetry in the initial condition triggers the new instability in NH. This effect corresponds to the recently identified multi-azimuth angle (MAA) instability of supernova neutrino fluxes. Both cases show explicitly that solutions of the equations of collective flavor oscillations need not inherit the symmetries of initial conditions, although this has been universally assumed.
    Physical Review D 07/2013; 88(4). DOI:10.1103/PhysRevD.88.045031 · 4.86 Impact Factor

Publication Stats

14k Citations
1,068.66 Total Impact Points

Institutions

  • 1990–2014
    • Max Planck Institute of Physics
      München, Bavaria, Germany
  • 2013
    • Ruđer Bošković Institute
      Zagrabia, Grad Zagreb, Croatia
  • 2011
    • Dogus Universitesi
      İstanbul, Istanbul, Turkey
  • 2005–2010
    • CERN
      Genève, Geneva, Switzerland
  • 2009
    • University of Zaragoza
      • Faculty of Sciences (CIENCIAS)
      Caesaraugusta, Aragon, Spain
  • 2006
    • Technical University Darmstadt
      Darmstadt, Hesse, Germany
  • 1997–2005
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 2003
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 2002
    • Politecnico di Milano
      Milano, Lombardy, Italy
  • 2000
    • Max Planck Institute for Informatics
      Saarbrücken, Saarland, Germany
  • 1999
    • Technion - Israel Institute of Technology
      H̱efa, Haifa District, Israel
  • 1987–1991
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, California, United States
  • 1988–1989
    • CSU Mentor
      Long Beach, California, United States