G. Raffelt

Ruđer Bošković Institute, Zagrabia, Grad Zagreb, Croatia

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Publications (287)716.91 Total impact

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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.
    05/2014;
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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). · 6.73 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.
    01/2014;
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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. · 7.73 Impact Factor
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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. · 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. · 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; · 5.08 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).
    VizieR Online Data Catalog. 08/2013;
  • 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). · 4.69 Impact Factor
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    ABSTRACT: The CERN Axion Solar Telescope (CAST) has finished its search for solar axions with 3^He buffer gas, covering the search range 0.64 eV < m_a <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 g_ag < 3.3 x 10^{-10} GeV^{-1} at 95% CL, with the exact value depending on the pressure setting. Future direct solar axion searches will focus on increasing the sensitivity to smaller values of g_a, for example by the currently discussed next generation helioscope IAXO.
    07/2013;
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    ABSTRACT: We use cosmological observations in the post-Planck era to derive limits on thermally produced cosmological axions. In the early universe such axions contribute to the radiation density and later to the hot dark matter fraction. We find an upper limit m_a < 0.67 eV at 95% C.L. after marginalising over the unknown neutrino masses, using CMB temperature and polarisation data from Planck and WMAP respectively, the halo matter power spectrum extracted from SDSS-DR7, and the local Hubble expansion rate H_0 released by the Carnegie Hubble Program based on a recalibration of the Hubble Space Telescope Key Project sample. Leaving out the local H_0 measurement relaxes the limit somewhat to 0.86 eV, while Planck+WMAP alone constrain the axion mass to 1.01 eV, the first time an upper limit on m_a has been obtained from CMB data alone. Our axion limit is therefore not very sensitive to the tension between the Planck-inferred H_0 and the locally measured value. This is in contrast with the upper limit on the neutrino mass sum, which we find here to range from 0.27 eV at 95% C.L. combining all of the aforementioned observations, to 0.84 eV from CMB data alone.
    Journal of Cosmology and Astroparticle Physics 07/2013; · 6.04 Impact Factor
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    ABSTRACT: Standard Model extensions often predict low-mass and very weakly interacting particles, such as the axion. A number of small-scale experiments at the intensity/precision frontier are actively searching for these elusive particles, complementing searches for physics beyond the Standard Model at colliders. Whilst a next generation of experiments will give access to a huge unexplored parameter space, a discovery would have a tremendous impact on our understanding of fundamental physics.
    Annalen der Physik 06/2013; 525(6). · 1.51 Impact Factor
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    Javier Redondo, Georg Raffelt
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    ABSTRACT: We re-examine solar emission of hidden photons gamma' (mass m) caused by kinetic mixing. We calculate the emission rate with thermal field theory methods and with a kinetic equation that includes "flavor oscillations" and photon absorption and emission by the thermal medium. In the resonant case both methods yield identical emission rates which, in the longitudinal channel, are enhanced by a factor w_P^2/m^2 (plasma frequency w_P) in agreement with An, Pospelov and Pradler (2013). The Sun must not emit more energy in a "dark channel" than allowed by solar neutrino measurements, i.e., not more than 10% of its photon luminosity. Together with the revised emission rate, this conservative requirement implies a bound \chi<4\times 10^-12 eV/m for the kinetic mixing parameter. This is the most restrictive stellar limit below m ~ 3 eV, whereas for larger masses the transverse channel dominates together with limits from other stars. A recent analysis of XENON10 data marginally improves the solar limit, leaving open the opportunity to detect solar hidden photons with future large-scale dark matter experiments. Detecting low-mass hidden photons with the ALPS-II photon-regeneration experiment also remains possible.
    Journal of Cosmology and Astroparticle Physics 05/2013; 2013(08). · 6.04 Impact Factor
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    ABSTRACT: Globular clusters have been used for a long time to test stellar evolution theories, and in particular to constrain novel forms of energy loss in low-mass stars. This includes constraints on axion properties, neutrino dipole moments, milli-charged particles, Kaluza-Klein gravitons, and many other phenomena. Depending on their interaction strength, these particles can be abundantly produced in stellar interiors, escape without further interaction, and thus drain energy directly from the stellar interior. Hence, they contribute directly to the stellar energy losses, thus modifying stellar evolution. Our goal is to re-examine such constraints in the light of modern data and updated stellar evolution codes, paying particular attention to systematic and statistical errors. As a first example, we consider the case of a neutrino magnetic moment that enhances the energy loss from the plasma process. In terms of the observed color-magnitude diagrams, the tip of the red giant branch (RGB) has been identified as a sensitive observable of the effects of the energy losses due to a neutrino magnetic moment. Here we describe the consequences of adding the cooling effect due to a neutrino magnetic moment to the Princeton-Goddard-PUC (PGPUC) stellar evolution code, exploring in particular the dependence of the position of the RGB tip on the neutrino magnetic moment. As a first application, we studied the position of the observed RGB tip in the case of the Galactic globular cluster M5 (NGC 5904), using the latest, high-precision, ground-based data from the P. B. Stetson database (2012, priv. comm.). We compare the empirical results with the PGPUC model predictions, and discuss the implied constraints on the value of the neutrino magnetic moment.
    03/2013;
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    ABSTRACT: In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axio-recombination, the "BCA processes." Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling g_ae and axion-photon interaction strength g_ag using the CAST phase-I data (vacuum phase). For m_a < 10 meV/c2 we find g_ag x g_ae< 8.1 x 10^-23 GeV^-1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission.
    Journal of Cosmology and Astroparticle Physics 02/2013; 1305(010). · 6.04 Impact Factor
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    ABSTRACT: The International Axion Observatory (IAXO) is a next generation axion helioscope aiming at a sensitivity to the axion-photon coupling of a few 10^{-12} GeV^{-1}, i.e. 1-1.5 orders of magnitude beyond sensitivities achieved by the currently most sensitive axion helioscope, the CERN Axion Solar Telescope (CAST). Crucial factors in improving the sensitivity for IAXO are the increase of the magnetic field volume together with the extensive use of x-ray focusing optics and low background detectors, innovations already successfully tested at CAST. Electron-coupled axions invoked to explain the white dwarf cooling, relic axions, and a large variety of more generic axion-like particles (ALPs) along with other novel excitations at the low-energy frontier of elementary particle physics could provide additional physics motivation for IAXO.
    02/2013;
  • Georg Raffelt
    Physcs Online Journal. 02/2013;
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    ABSTRACT: To study the capabilities of supernova neutrino detectors, the instantaneous spectra are often represented by a quasi-thermal distribution of the form f(E) = E^alpha e^{-(alpha+1)E/E_{av}} where E_{av} is the average energy and alpha a numerical parameter. Based on a spherically symmetric supernova model with full Boltzmann neutrino transport we have, at a few representative post-bounce times, re-converged the models with vastly increased energy resolution to test the fit quality. For our examples, the spectra are well represented by such a fit in the sense that the counting rates for a broad range of target nuclei, sensitive to different parts of the spectrum, are reproduced very well. Therefore, the mean energy and root-mean-square energy of numerical spectra hold enough information to provide the correct alpha and to forecast the response of multi-channel supernova neutrino detection.
    Physical review D: Particles and fields 11/2012; 86(12).

Publication Stats

9k Citations
716.91 Total Impact Points

Institutions

  • 2013
    • Ruđer Bošković Institute
      Zagrabia, Grad Zagreb, Croatia
  • 1993–2013
    • Max Planck Institute of Physics
      München, Bavaria, Germany
  • 2004–2012
    • University of Naples Federico II
      • Department of Physical Sciences
      Napoli, Campania, Italy
  • 2011
    • Dogus Universitesi
      İstanbul, Istanbul, Turkey
  • 1997–2010
    • CERN
      Genève, Geneva, Switzerland
    • Aarhus University
      • Department of Physics and Astronomy
      Aars, Region North Jutland, Denmark
  • 2009
    • University of Zaragoza
      • Faculty of Sciences (CIENCIAS)
      Caesaraugusta, Aragon, Spain
    • University of Valencia
      Valenza, Valencia, Spain
  • 2002
    • University of Oxford
      Oxford, England, United Kingdom
  • 2000
    • Russian Academy of Sciences
      • Institute of Nuclear Research
      Moscow, Moscow, Russia
  • 1999
    • Technion - Israel Institute of Technology
      H̱efa, Haifa District, Israel
  • 1996
    • Wake Forest University
      Winston-Salem, North Carolina, United States
  • 1987–1996
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, CA, United States
  • 1988–1989
    • CSU Mentor
      Long Beach, California, United States
    • Kyoto University
      Kioto, Kyōto, Japan