Search

IceCube, a future km^3 antarctic ice Cherenkov neutrino telescope, is highly sensitive to a galactic supernova (SN) neutrino burst. The Cherenkov light corresponding to the total energy deposited by the SN neutrinos in the ice can be measured relative to background fluctuations with a statistical precision much better than 1%. If the SN is viewed through the Earth, the matter effect on neutrino oscillations can change the signal by more than 5%, depending on the flavor-dependent source spectra and the neutrino mixing parameters. Therefore, IceCube together with another high-statistics experiment like Hyper-Kamiokande can detect the Earth effect, an observation that would identify specific neutrino mixing scenarios that are difficult to pin down with long-baseline experiments. In particular, the normal mass hierarchy can be clearly detected if the third mixing angle is not too small, sin^2 theta_13 < 10^-3. The small flavor-dependent differences of the SN neutrino fluxes and spectra that are found in state-of-the-art simulations suffice for this purpose. Although the absolute calibration uncertainty at IceCube may exceed 5%, the Earth effect would typically vary by a large amount over the duration of the SN signal, obviating the need for a precise calibration. Therefore, IceCube with its unique geographic location and expected longevity can play a decisive role as a "co-detector" to measure SN neutrino oscillations. It is also a powerful stand-alone SN detector that can verify the delayed-explosion scenario., Comment: 19 pages, 6 Figs, final version accepted by JCAP, some references added

Transporting nu_mu and nu_tau in a supernova (SN) core involves several processes that have been neglected in traditional simulations. Based on a Monte Carlo study we find that the flavor-dependent spectral differences are much smaller than is often stated in the literature. A full-scale SN simulation using a Boltzmann solver and including all relevant neutrino reactions confirms these results. The flavor-dependent flux differences are largest during the initial accretion phase., Comment: Proceedings NOON 03, Kanazawa, 10-14 Feb 2003

The observed flavor oscillations of solar and atmospheric neutrinos determine several elements of the leptonic mixing matrix, but leave open the small mixing angle Theta_13, a possible CP-violating phase, the mass ordering, the absolute mass scale m_nu, and the Dirac vs. Majorana property. Progress will be made by long-baseline, tritium endpoint, and 2-beta decay experiments. The best constraint on m_nu obtains from cosmological precision observables, implying that neutrinos contribute very little to the dark matter. However, massive Majorana neutrinos may well be responsible for ordinary matter by virtue of the leptogenesis mechanism for creating the baryon asymmetry of the universe. In future, neutrinos could play an important role as astrophysical messengers if point sources are discovered in high-energy neutrino telescopes. In the low-energy range, a high-statistics observation of a galactic supernova would allow one to observe directly the dynamics of stellar collapse and perhaps to discriminate between certain mixing scenarios. An observation of the relic neutrinos from all past supernovae has come within reach., Comment: Proceedings Texas in Tuscany, Dec. 2002. Updated cosmological mass limits in replacement

We review the role of massive neutrinos in astrophysics and cosmology, assuming that the oscillation interpretation of solar and atmospheric neutrinos is correct. In particular, we discuss cosmological mass limits, neutrino flavor oscillations in the early universe, leptogenesis, and neutrinos in core-collapse supernovae., Comment: Procs. International School of Physics ``Enrico Fermi,'' CLII Course ``Neutrino Physics,'' 23 July-2 August 2002, Varenna, Lake Como, Italy. Additional references in revised version

Stars are powerful sources for weakly interacting particles that are produced by nuclear or plasma processes in their hot interior. These fluxes can be used for direct measurements (e.g. solar or supernova neutrinos) or the back-reaction on the star can be used to derive limits on new particles. We discuss two examples of current interest, the search for solar axions by the CAST experiment at CERN and stellar-evolution limits on the size of putative large extra dimensions., Comment: Contribution to ESO-CERN-ESA Symposium on Astronomy, Cosmology and Fundamental Physics (4-7 March 2002, Garching, Germany), additional references in revised version

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., Comment: Contribution to Dennis Sciama Memorial Volume of NAR, additional references and reference updates in revised version

Spherically symmetric simulations of stellar core collapse and post-bounce evolution are used to test the sensitivity of the supernova dynamics to different variations of the input physics. We consider a state-of-the-art description of the neutrino-nucleon interactions, possible lepton-number changing neutrino reactions in the neutron star, and the potential impact of hydrodynamic mixing behind the supernova shock., Comment: 6 pages, 6 ps figures (in color), to appear in W. Hillebrandt and E. Mueller, eds., Proceedings of the 11th Workshop on "Nuclear Astrophysics" held at Ringberg Castle, February 11-16, 2002

We study three-flavor neutrino oscillations in the early universe in the presence of neutrino chemical potentials. We take into account all effects from the background medium, i.e. collisional damping, the refractive effects from charged leptons, and in particular neutrino self-interactions that synchronize the neutrino oscillations. We find that effective flavor equilibrium between all active neutrino species is established well before the big-bang nucleosynthesis (BBN) epoch if the neutrino oscillation parameters are in the range indicated by the atmospheric neutrino data and by the large mixing angle (LMA) MSW solution of the solar neutrino problem. For the other solutions of the solar neutrino problem, partial flavor equilibrium may be achieved if the angle theta_13 is close to the experimental limit tan^2(theta_13)<0.065. In the LMA case, the BBN limit on the nu_e degeneracy parameter, |xi_nu|< 0.07, now applies to all flavors. Therefore, a putative extra cosmic radiation contribution from degenerate neutrinos is limited to such low values that it is neither observable in the large-scale structure of the universe nor in the anisotropies of the cosmic microwave background radiation. Existing limits and possible future measurements, for example in KATRIN, of the absolute neutrino mass scale will provide unambiguous information on the cosmic neutrino mass density, essentially free of the uncertainty of the neutrino chemical. potentials., Comment: 25 pages, 10 figures, version to be published in NPB

Core-collapse supernovae (SNe) are powerful neutrino sources and as such important targets for the growing array of neutrino observatories. We review the current status of SN theory and the expected characteristics of the neutrino signal. After recalling what we have learned from SN 1987A and general SN properties we review the physics potential of a future galactic SN observation., Comment: Contribution to TAUP 2001

In the early universe or in some regions of supernovae, the neutrino refractive index is dominated by the neutrinos themselves. Several previous studies have found numerically that these self-interactions have the effect of coupling different neutrino modes in such a way as to synchronize the flavor oscillations which otherwise would depend on the energy of a given mode. We provide a simple explanation for this baffling phenomenon in analogy to a system of magnetic dipoles which are coupled by their self-interactions to form one large magnetic dipole which then precesses coherently in a weak external magnetic field. In this picture the synchronized neutrino oscillations are perfectly analogous to the weak-field Zeeman effect in atoms., Comment: 7 pages, 3 figures

The mu- and tau-neutrinos emitted from a proto-neutron star are produced by nucleonic bremsstrahlung N + N -> N + N + nu + nu-bar and pair annihilation e^+ + e^- -> nu + nu-bar, reactions which freeze out at the "energy sphere." Before escaping from there to infinity the neutrinos diffuse through the "scattering atmosphere," a layer where their main interaction is elastic scattering on nucleons nu + N -> N + nu. If these collisions are taken to be iso-energetic as in all numerical supernova simulations, the neutrino flux spectrum escaping to infinity depends only on the medium temperature T_ES and the thermally averaged optical depth tau_ES at the energy sphere. For tau_ES = 10-50 one finds for the spectral flux temperature of the escaping neutrinos T_flux = 0.5-0.6 T_ES. Including energy exchange (nucleon recoil) in nu + N -> N + nu can shift T_flux both up or down. Delta T_flux depends on tau_ES, on the scattering atmosphere's temperature profile, and on T_ES. Based on a numerical study we find that for typical conditions Delta T_flux/T_flux is between -10% and -20%, and even for extreme parameter choices does not exceed -30%. The exact value of Delta T_flux/T_flux is surprisingly insensitive to the assumed value of the nucleon mass, i.e. the exact efficiency of energy transfer between neutrinos and nucleons is not important as long as it can occur at all. Therefore, calculating the nu_mu and nu_tau spectra does not seem to require a precise knowledge of the nuclear medium's dynamical structure functions., Comment: 30 pages, 24 figures, Revised version with several clarifications in the text, no changes of substance

If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from BL Lacertae at cosmological distances as suggested by recent studies, the absence of the GZK cutoff can not be reconciled with Standard-Model particle properties. Axions would escape the GZK cutoff, but even the coherent conversion and back-conversion between photons and axions in large-scale magnetic fields is not enough to produce the required flux. However, one may construct models of other novel (pseudo)scalar neutral particles with properties that would allow for sufficient rates of particle production in the source and shower production in the atmosphere to explain the observations. As an explicit example for such particles we consider SUSY models with light sgoldstinos., Comment: 5 pages, 2 postscript figures, ref. added

Cosmological and astrophysical effects of heavy (10 - 200 MeV) sterile Dirac neutrinos, mixed with the active ones, are considered. The bounds on mass and mixing angle from both supernovae and big-bang nucleosynthesis are presented., Comment: 19 pages, 5 figures, 1 table. Some references added

We explore the physics potential of a terrestrial detector for observing axionic Kaluza-Klein excitations coming from the Sun within the context of higher-dimensional theories of low-scale quantum gravity. In these theories, the heavier Kaluza-Klein axions are relatively short-lived and may be detected by a coincidental triggering of their two-photon decay mode. Because of the expected high multiplicity of the solar axionic excitations, we find experimental sensitivity to a fundamental Peccei-Quinn axion mass up to $10^{-2}$ eV (corresponding to an effective axion-photon coupling $g_{a\gamma \gamma} \approx 2.\times 10^{-12}$ GeV$^{-1}$) in theories with 2 extra dimensions and a fundamental quantum-gravity scale $M_{\rm F}$ of order 100 TeV, and up to $3.\times 10^{-3}$ eV (corresponding to $g_{a\gamma \gamma} \approx 6.\times 10^{-13}$ GeV$^{-1}$) in theories with 3 extra dimensions and $M_{\rm F}=1$ TeV. For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits: $g_{a \gamma \gamma} \stackrel{<}{{}_\sim} 2.5\times 10^{-11}$ GeV$^{-1}$ and $g_{a \gamma \gamma} \stackrel{<}{{}_\sim} 1.2\times 10^{-11}$ GeV$^{-1}$ in the aforementioned theories with 2 and 3 large compact dimensions, respectively., Comment: 19 pages, extended version, as to appear in Physical Review D

Constraints on the lifetime of the heavy sterile neutrino, that was proposed as a possible interpretation of the KARMEN anomaly, are derived from primordial nucleosynthesis and SN 1987A. Together with the recent experimental bounds on the nu_s lifetime, SN 1987A completely excludes this interpretation. Nucleosynthesis arguments permit a narrow window for the lifetime in the interval 0.1-0.2 sec. If nu_s possesses an anomalous interaction with nucleons, the SN bounds may not apply, while the nucleosynthesis ones would remain valid., Comment: Figure 7 changed. (30 pages, 7 ps-figures, 2 tables. Subm to NPB)

An introduction to various topics in neutrino astrophysics is given for students with little prior exposure to this field. We explain neutrino production and propagation in stars, neutrino oscillations, and experimental searches for this effect. We also touch upon the cosmological role of neutrinos. A number of exercises is also included., Comment: Lecture held by G. Raffelt at the 4th national Summer School "Grundlagen und neue Methoden der theoretischen Physik", 31 August -- 11 September 1998 in Saalburg, Germany, 46 pages, 9 figures

We study if the neutrino mixing parameters suggested by the atmospheric neutrino anomaly imply chemical equilibrium between mu- and tau-flavored leptons in a supernova (SN) core. The initial flavor-conversion rate would indeed be fast if the nu_mu-nu_tau-mixing angle were not suppressed by second-order refractive effects. The neutrino diffusion coefficients are different for nu_mu, anti-nu_mu, nu_tau and anti-nu_tau so that neutrino transport will create a net mu and tau lepton number density. This will typically lead to a situation where the usual first-order refractive effects dominate, further suppressing the rate of flavor conversion. Altogether, neutrino refraction has the nontrivial consequence of guaranteeing the separate conservation of e, mu, and tau lepton number in a SN core on the infall and cooling time scales, even when neutrino mixing angles are large., Comment: Slightly expanded version with improved presentation, no changes of substance

Low-mass particles such as neutrinos, axions, other Nambu-Goldstone bosons and gravitons are produced in the hot and dense interior of stars. Therefore, astrophysical arguments constrain the properties of these particles in ways which are often complementary to cosmological arguments and to laboratory experiments. This review provides an update on the most important stellar-evolution limits and discusses them in the context of other information from cosmology and laboratory experiments., Comment: 46 pages, including 14 eps figures, prepared for vol.49 of the Annual Review of Nuclear and Particle Science (1999)

Nonstandard neutrino properties (masses, mixing, sterile states, electromagnetic interactions, and so forth) can have far-reaching ramifications in astrophysics and cosmology. We look at the most interesting cases in the light of the powerful current indications for neutrino oscillations., Comment: 40 pages, 14 eps-figs, to be publ. in Proc. 1998 Summer School in High-Energy Physics and Cosmology, ICTP, Trieste, Italy, 29 June - 17 July 1998, ed. by G.Senjanovic and A.Yu.Smirnov (World Scientific, Singapore)

We discuss the Cherenkov process $\nu\to\nu\gamma$ in the presence of a homogeneous magnetic field. The neutrinos are taken to be massless with only standard-model couplings. The magnetic field fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation such that the Cherenkov condition $\omega<|{\bf k}|$ is fulfilled. For a field strength $B_{\rm crit}=m_e^2/e=4.41\times10^{13} Gauss$ and for $E=2m_e$ the Cherenkov rate is about $6\times10^{-11}s^{-1}$., Comment: Talk given at 4th SFB-375 Ringberg Workshop on Neutrino Astrophysics Ringberg Castle, Tegernsee, Germany, 20-24 Oct 1997

Recent observations of TeV gamma rays from distant sources provide new limits on the cosmic infrared background and thus on radiative decays of background neutrinos. I translate these limits into bounds on transition dipole moments and compare them with limits from the energy-loss of globular-cluster stars. The latter are more restrictive for neutrino masses below 1-2 eV., Comment: 1 page, including 1 eps fig

In a supernova core, magnetic fields cause a directional variation of the neutrino refractive index so that resonant flavor oscillations would lead to a deformation of the "neutrinosphere" for, say, tau neutrinos. The associated anisotropic neutrino emission was proposed as a possible origin of the observed pulsar proper motions. We argue that this effect was vastly overestimated because the variation of the temperature over the deformed neutrinosphere is not an adequate measure for the anisotropy of neutrino emission. The neutrino flux is generated inside the neutron star core and is transported through the atmosphere at a constant luminosity, forcing the temperature gradient in the atmosphere to adjust to the inflow of energy from below. Therefore, no emission anisotropy is caused by a deformation of the neutrinosphere to lowest order. An estimate of the higher-order corrections must take into account the modified atmospheric temperature profile in response to the deformation of the neutrinosphere and the corresponding feedback on the core. We go through this exercise in the framework of a simplified model which can be solved analytically., Comment: Final version with minor corrections, to be published in PRD. Includes a "Note Added" in response to astro-ph/9811144

Positive evidence for neutrino oscillations is mounting from the solar and atmospheric neutrino anomalies and the LSND experiment. Accordingly, the neutrino mass differences appear to lie in the sub-eV range and at least some of the mixing angles appear to be large. We explore some of the consequences of this picture for supernova (SN) physics and cosmology. In particuler, we discuss if a conflict between the solar vacuum solution and the SN 1987A signal can be avoided, and the role of future cosmic microwave background measurements to reveal the presence of a cosmological hot dark matter component., Comment: 9 pages, 3 eps figs included, to be publ. in Proc. New Trends in Neutrino Physics, 24-29 May 1998, Ringberg Castle, Tegernsee, Germany

The status of several current and proposed experiments to search for galactic dark-matter and solar axions is reviewed in the light of astrophysical and cosmological limits on the Peccei-Quinn scale., Comment: 6 pages, 4 eps figs, to be published in Proc. Neutrino 98, 4-9 June 1998, Takayama, Japan, ed. by Y.Suzuki and Y.Totsuka

If axions exist, they are copiously produced in hot and dense plasmas, carrying away energy directly from the interior of stars. Various astronomical observables constrain the operation of such anomalous stellar energy-loss channels and thus provide restrictive limits on the axion interactions with photons, nucleons, and electrons. In typical axion models a limit m_a < 0.01 eV is implied. The main arguments leading to this result are explained, including more recent work on the important supernova 1987A constraint., Comment: 11 pages, 12 eps figs, to be published in Proc. AXION WORKSHOP, Gainesville, Florida, 13-15 March 1998, ed. by P.Sikivie

The bremsstrahlung process Nu_Tau -> Nu_e E+ E- Gamma is the dominant photon-producing decay of heavy Tau neutrinos with m_Nu_Tau > 2 m_e so that this process is instrumental for supernova 1987A constraints on the properties of these particles, notably on their mixing amplitude with Nu_e. We calculate the rate of the bremsstrahlung process as well as the photon spectrum and the angular distribution relative to the spin direction of the parent neutrino. We carefully pay attention to the difference between Dirac and Majorana neutrinos., Comment: 6 pages, REVTEX, includes 5 eps figs

Magnetic fields mix axions with photons, allowing for the cyclotron process e -> e + a by virtue of an intermediate plasmon even if axions do not couple to electrons at tree level. The axion and longitudinal-plasmon dispersion relations always cross for a certain wave number, leading to a resonant enhancement of this process. Even then, however, it cannot quite compete with the usual nucleon processes in a supernova core. The well-known axion window 10^{-5} eV < m_a < 10^{-2} eV remains open and axions may still constitute the cosmic dark matter., Comment: 5 pages, REVTEX, 3 eps figs included

Collection of "Extended Abstracts" of talks presented at the SFB-375 workshop NEUTRINO ASTROPHYSICS, Ringberg Castle, Tegernsee, Germany, 20-24 Oct. 1997. Topics include Solar Neutrinos, Supernovae, Gamma-Ray Bursts, High-Energy Neutrinos (atmospheric, astrophysical), Cosmology, and Future Prospects. The focus is on astrophysical and experimental/observational aspects of astrophysical neutrinos while particle theory and neutrino laboratory experiments are not covered., Comment: LaTeX 8+196 pages, including many eps figures. WARNING: Approx. 2.6 MB in compressed form. Individual contributions available at http://www.mpa-garching.mpg.de/SFB/ringberg_1997/

Recent developments of those areas of astro-particle physics are discussed that were represented at the HEP97 conference. In particular, the current status of direct and indirect dark-matter searches and of TeV neutrino and gamma-ray astronomy will be reviewed., Comment: 10 pages, 4 eps figures included, Proc. HEP97 Jerusalem, August 1997

The physical nature of most of the gravitating mass in the universe is completely mysterious. The astrophysical evidence for the presence of this dark matter and astrophysical constraints on its properties will be reviewed. The most popular dark-matter candidates will be introduced, and current and future attempts to search for them directly and indirectly will be discussed., Comment: 47 pages, 32 eps figures included, Lectures at European School of High-Energy Physics, Menstrup, Denmark, June 1997

Cosmology yields the most restrictive limits on neutrino masses and conversely, massive neutrinos would contribute to the cosmic dark-matter density and would play an important role for the formation of structure in the universe. Neutrino oscillations may well solve the solar neutrino problem and can have a significant impact on supernova physics. The neutrino signal from a future galactic supernova could provide evidence for cosmologically interesting neutrino masses or set interesting limits., Comment: 11 pages, 7 ps figures included, Contribution to Proc. TAUP97

While the photon forward-scattering amplitude on free magnetic dipoles (e.g. free neutrons) vanishes, the nucleon magnetic moments still contribute significantly to the photon dispersion relation in a supernova (SN) core where the nucleon spins are not free due to their interaction. We study the frequency dependence of the relevant spin susceptibility in a toy model with only neutrons which interact by one-pion exchange. Our approach amounts to calculating the photon absorption rate from the inverse bremsstrahlung process gamma n n --> n n, and then deriving the refractive index n_refr with the help of the Kramers-Kronig relation. In the static limit (omega --> 0) the dispersion relation is governed by the Pauli susceptibility chi_Pauli so that (n_refr)^2-1 approx chi_Pauli > 0. For omega somewhat above the neutron spin-relaxation rate Gamma_sigma we find (n_refr)^2-1< 0, and for omega >> Gamma_sigma the photon dispersion relation acquires the form omega^2-k^2=(m_gamma)^2. An exact expression for the "transverse photon mass" m_gamma is given in terms of the f-sum of the neutron spin autocorrelation function; an estimate is (m_gamma)^2 approx chi_Pauli T Gamma_sigma. The dominant contribution to n_refr$ in a SN core remains the electron plasma frequency so that the Cherenkov processes gamma nu <--> nu remain forbidden for all photon frequencies., Comment: 8 pages, REVTEX, 7 postscript figures included

A massive long-lived tau neutrino in the MeV regime modifies the primordial light-element abundances predicted by big-bang nucleosynthesis (BBN) calculations. This effect has been used to derive limits on the tau neutrino mass. Because recently the observational situation has become somewhat confusing and, in part, intrinsically inconsistent, we reconsider the BBN limits on the tau neutrino mass. To this end we use our newly developed BBN code to calculate the primordial abundances as a function of the tau neutrino mass and of the cosmic baryon density eta. We derive concordance regions in the eta - tau-neutrino-mass - plane for several sets of alleged primordial abundances. In some cases a concordance region exists only for a nonvanishing tau neutrino mass. At the present time BBN does not provide clear evidence for or against a tau neutrino mass., Comment: 10 pages, latex-file, uses l-aa.sty and psfig.sty, 18 ps figures included; accepted by Astronomy & Astrophysics; Replaced to match version accepted for publication (08/97); misprint in Eq. (A3) corrected (04/00)

Pseudoscalar particles $\phi$ usually couple electromagnetically by an interaction of the form $\frc14 g \phi F {\widetilde F}$, allowing them to convert to photons in the presence of magnetic fields. Notably, new low-mass pseudoscalars emitted from supernova (SN) 1987A would have been converted to $\gamma$-rays in the intervening magnetic field of the galaxy. Therefore, measurements by the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS) can limit the inverse coupling constant to $g^{-1}>1{\times}10^{11}\,\rm GeV$, assuming the pseudoscalar is massless. This is an improvement over other astrophysical limits of a factor of about 2.5., Comment: 10 pages, plus 4 PostScript files (included)

In a nuclear medium, spin-dependent forces cause the nucleon spins to fluctuate with a rate $\Gamma_\sigma$. We have previously shown that as a consequence the effective axial-current neutrino-nucleon scattering cross section is reduced. Here, we calculate this reduction explicitly in the perturbative limit $\Gamma_\sigma\ll T$. By virtue of an exact sum rule of the spin-density structure function, we express the modified cross section in terms of the matrix element for neutrino-nucleon scattering in the presence of a spin-dependent nuclear potential. This representation allows for a direct comparison with and confirmation of Sawyer's related perturbative result. In a supernova core with a typical temperature $T=10\,\rm MeV$, the perturbative limit is relevant for densities $\rho\alt10^{13}\,\rm g\,cm^{-3}$ and thus applies around the neutrino sphere. There, the cross-section reduction is of order a few percent and thus not large; however, a new mode of energy transfer between neutrinos and nucleons is enabled which may be important for neutrino spectra formation. We derive an analytic perturbative expression for the rate of energy transfer., Comment: 9 pages, REVTeX, 4 postscript figures. Submitted to Phys. Rev. D

We study the impact of neutrino oscillations on the interpretation of the supernova (SN) 1987A neutrino signal by means of a maximum-likelihood analysis. We focus on oscillations between $\overline\nu_e$ with $\overline\nu_\mu$ or $\overline\nu_\tau$ with those mixing parameters that would solve the solar neutrino problem. For the small-angle MSW solution ($\Delta m^2\approx10^{-5}\,\rm eV^2$, $\sin^22\Theta_0\approx0.007$), there are no significant oscillation effects on the Kelvin-Helmholtz cooling signal; we confirm previous best-fit values for the neutron-star binding energy and average spectral $\overline\nu_e$ temperature. There is only marginal overlap between the upper end of the 95.4\% CL inferred range of $\langle E_{\overline\nu_e}\rangle$ and the lower end of the range of theoretical predictions. Any admixture of the stiffer $\overline\nu_\mu$ spectrum by oscillations aggravates the conflict between experimentally inferred and theoretically predicted spectral properties. For mixing parameters in the neighborhood of the large-angle MSW solution ($\Delta m^2\approx10^{-5}\,\rm eV^2$, $\sin^22\Theta_0\approx0.7$) the oscillations in the SN are adiabatic, but one needs to include the regeneration effect in the Earth which causes the Kamiokande and IMB detectors to observe different $\overline\nu_e$ spectra. For the solar vacuum solution ($\Delta m^2\approx10^{-10}\,\rm eV^2$, $\sin^22\Theta_0\approx1$) the oscillations in the SN are nonadiabatic; vacuum oscillations take place between the SN and the detector. If either of the large-angle solutions were borne out by the upcoming round of solar neutrino experiments, one would have to conclude that the SN~1987A $\overline\nu_\mu$ and/or $\overline\nu_e$ spectra had been much softer than predicted by current, Comment: Final version with very minor wording changes, to be published in Phys. Rev. D

A variation of Newton's constant $G$ over cosmological time scales would modify the main-squence time of globular cluster (GC) stars. We have calculated the evolution of low-mass stars typical for GCs both for standard non-varying $G$ and under the assumption of a linear variation of $G$. The age of the isochrones resulting from the latter models then was chosen such that the isochrones mimicked the standard ones at the turnoff. Assuming that the true age of GCs is between $8$ and $20\,\rm Gyr$, and because their apparent age is between $14$ and $18\,\rm Gyr$, we find that today $-35{\times}10^{-12}\,{\rm yr}^{-1}\la\dot{G}/G\la 7{\times}10^{-12}\,{\rm yr}^{-1}$. The upper limit (gravity weaker in the past) is competitive with direct present-day bounds from celestial mechanics. Within independently determined $\dot{G}/G$ limits a time-varying $G$ as an explanation for the discrepancy between the cosmic expansion age and the apparent GC ages is conceivable., Comment: uu-encoded and compressed postscript version of the paper with figures

In the hot and dense medium of a supernova (SN) core, the nucleon spins fluctuate so fast that the axial-vector neutrino opacity and the axion emissivity are expected to be significantly modified. Axions with $m_a\alt10^{-2}\,{\rm eV}$ are not excluded by SN~1987A. A substantial transfer of energy in neutrino-nucleon ($\nu N$) collisions is enabled which may alter the spectra of SN neutrinos relative to calculations where energy-conserving $\nu N$ collisions had been assumed near the neutrinosphere., Comment: 8 pages. REVTeX. 2 postscript figures, can be included with epsf. Small modifications of the text, a new "Note Added", and three new references. To be published in Phys. Rev. Lett

In the light of the $\nu_\mu\to\nu_e$ neutrino oscillations which may have been observed at the LSND experiment we explore the consequences of two inverted mass schemes where solar neutrino oscillations occur between $\nu_e$ and $\nu_\tau$. The favored LSND value $\Delta m^2=6\,\eV^2$ leads to $m_{\nu_e}\approx m_{\nu_\tau}\approx 2.5\,\eV$ and $m_{\nu_\mu}\approx0$ so that cosmology can benefit from a recently proposed ``cold plus hot dark matter'' structure formation scenario with two equal mass light neutrinos (C$\nu^2$DM). Solar neutrino oscillations ($\nu_e\to\nu_\tau$) can occur with one of the large mixing angle solutions so that a serious conflict with $\beta\beta$ decay Majorana mass limits is avoided without invoking Dirac masses. However, there is a problem with the SN~1987A signal because of resonant $\anti\nu_e\leftrightarrow\anti\nu_\mu$ oscillations which are expected to cause far higher $\anti\nu_e$ energies at the IMB and Kamiokande~II detectors than have been observed. A small value $\Delta m^2=0.5\,\eV^2$ at LSND, which allows for a relatively large $\nu_e$-$\nu_\mu$ mixing angle without conflicting with the KARMEN and BNL-E776 experiments, would indicate $m_{\nu_e}\approx m_{\nu_\tau}\approx 1.62\,\eV$ and $m_{\nu_\mu}\approx1.77\,\eV$. This scheme of C$\nu^3$DM maintains, and even may improve, the essential cosmological model implications for large-scale structure, leaving no conflict with SN r-process nucleosynthesis. It may improve the discordance between the SN~1987A neutrino spectra inferred from Kamiokande~II and IMB., Comment: uuencoded and compressed postscript file, includes 2 figures.

If axions or other low-mass pseudoscalars couple to electrons (``fine structure constant'' $\alpha_a$) they are emitted from red giant stars by the Compton process $\gamma+e\to e+a$ and by bremsstrahlung $e+(Z,A)\to (Z,A)+e+a$. We construct a simple analytic expression for the energy-loss rate for all conditions relevant for a red giant and include axion losses in evolutionary calculations from the main sequence to the helium flash. We find that $\alpha_a\lapprox0.5\mn(-26)$ or $m_a\lapprox 9\,\meV/\cos^2\beta$ lest the red giant core at helium ignition exceed its standard mass by more than $0.025\,\MM_\odot$, in conflict with observational evidence. Our bound is the most restrictive limit on $\alpha_a$, but it does not exclude the possibility that axion emission contributes significantly to the cooling of ZZ~Ceti stars such as G117--B15A for which the period decrease was recently measured., Comment: 11 pages, uuencoded and compressed postscript file

On the basis of Braaten and Segel's representation of the electromagnetic dispersion relations in a QED plasma we check the numerical accuracy of several published analytic approximations to the plasma neutrino emission rates. As we find none of them satisfactory we derive a new analytic approximation which is accurate to within 4\%\ where the plasma process dominates. The correct emission rates in the parameter regime relevant for the red giant branch in globular clusters are larger by about $10-20$\% than those of previous stellar evolution calculations. Therefore, the core mass of red giants at the He flash is larger by about $0.005\M_\odot$ or 1\% than previously thought. Our bounds on neutrino magnetic dipole moments remain virtually unchanged., Comment: LaTeX, 16 pages, 12 figures on request from authors, MPI-Ph/93-65

We consider particle oscillations and their damping in second-quantized form. We find that the damping or "decoherence" may be described by a Boltzmann-like collision integral with "non-abelian blocking factors" (fermions). Earlier results are generalized in that the momentum degrees of freedom are included and that the mixing equations become intrinsically non-linear at high densities., Comment: 12 pages, no figures, PLAIN-TeX, Preprint MPI-Ph/92-65

If $\nu_\mu$ or $\nu_\tau$ mix with $\nu_e$, neutrino oscillations and collisions in a supernova (SN) core allow these flavors effectively to participate in $\beta$ equilibrium and thus to obtain a large chemical potential. If a sterile species mixes with $\nu_e$, these effects lead to an anomalous loss of energy and lepton number. We study flavor conversion in a SN core on the basis of a new kinetic equation which rigorously includes neutrino interference and degeneneracy effects. Our discussion serves as an example and illustration of the properties of this ``non-abelian Boltzmann equation''., Comment: 24 pages, 3 figures from authors upon request, LaTeX, MPI-Ph/92-68