15332448
Relic neutrino background from cosmological supernovae
Present and future observations of supernova relic neutrinos (SRNs), i.e., a cosmological neutrino background from past core-collapse supernova explosions, potentially give us useful information concerning various fields of astrophysics, cosmology and particle physics. We review recent progress of theoretical and observational studies of SRNs, particularly focusing on the detectability, and also on implications for cosmic star formation history and neutrino physics.
125701625
Gamma-ray burst neutrino background and star formation history in the universe
Abstract We estimate the flux of the GRB neutrino background and compute the event rate at SK and TITAND in the collapsar model, assuming that GRB formation rate is proportional to the star formation rate. We find that the predicted background neutrino flux is highly sensitive to unknown model parameters, mainly to the mass accretion rate, to the fraction of disk energy emitted in thermal neutrinos (as opposed to emission through electromagnetic processes), and to the fraction of collapsar events leading to GRBs. The predicted neutrino flux varies over many orders of magnitude as the values of unknown model parameters are varied. We investigate the detection possibility of thermal neutrinos from collapsars which lead to GRBs by TITAND. We find that the GRB neutrino background might be detected by TITAND within ∼ 10 yrs only for the optimistic cases in which the average mass-accretion rate is high (≥ a few M ⊙ s −1 ), and the probability that one collapsar generates a GRB is high ( φ = 0.5 − 1.0).
116431772
Supernova Neutrino Oscillations and the Neutrino Magnetic Moment
Resonant spin-flavour (RSF) conversions of supernova neutrinos, which are induced by the interaction between the nonzero neutrino magnetic moment and supernova magnetic fields, are studied for both normal and inverted mass hierarchy. As the case for the pure matter-induced neutrino oscillation (Mikheyev–Smirnov–Wolfenstein (MSW) effect), we find that the RSF transitions are strongly dependent on the neutrino mass hierarchy as well as the value of θ13. Flavour conversions are solved numerically for various neutrino parameter sets, with the realistic presupernova profile. In particular, it is very interesting that the RSF-induced νe → ν̄e transition occurs if the following conditions are all satisfied: the value of μνB (μν is the neutrino magnetic moment and B is the magnetic field strength) is sufficiently strong, the neutrino mass hierarchy is inverted, and the value of θ13 is large enough to induce adiabatic MSW resonance. In this case, the strong peak due to the original νe emitted from the neutronization burst would exist in the time profile of the neutrino events detected at the Super-Kamiokande detector. If this peak were observed in reality, it would provide fruitful information on the neutrino properties. On the other hand, the characteristics of the neutrino spectra are also different between the neutrino models, but we find that there remains degeneracy among several models. This contribution is based on our recent study [1].
119067583
Supernova Relic Neutrinos and Observational Implications for Neutrino Oscillation
We investigate the flux and the event rate of supernova relic neutrinos (SRN) at the Super-Kamiokande (SK) detector for various neutrino oscillation models with parameters inferred from recent experimental results. We discuss the detectability of SRN at SK, comparing this SRN flux with other background neutrinos in more detail than previous studies, and it is found that in the energy range 17–25 MeV, ten-year observation might enable us to detect SRN signal (at one sigma level). We also set 90% C.L. upper limit on the SRN flux for various oscillation models using the recently released observational result by SK. In addition, we propose that the SRN observation can be used to set strong constraints on the neutrino decay models. Because of the long distance scale from cosmological supernovae to the Earth, SRN have possibility to provide much stronger limit than the present one obtained from solar neutrino observation. In the near future, further reduced upper limit is actually expected, when the current SK data are reanalyzed using some technique to reduce background events against the SRN signals. It is expected that the reduced upper limit is sufficient to provide useful implications for neutrino oscillation and decaying neutrinos.
216052179
Constraints on the annihilation cross section of dark matter particles from anisotropies in the diffuse gamma-ray background measured with Fermi-LAT
Annihilation of dark matter particles in cosmological halos (including the halo of the Milky Way) contributes to the diffuse gamma-ray background (DGRB). As this contribution will appear anisotropic in the sky, one can use the angular power spectrum of anisotropies in the DGRB to constrain the properties of dark matter particles. By comparing the updated analytic model of the angular power spectrum of the DGRB from dark matter annihilation with the power spectrum recently measured from the 22-month data of the Fermi Large Area Telescope (LAT), we place upper limits on the annihilation cross section of dark matter particles as a function of dark matter masses. We find that the current data exclude (σv)≳10−25  cm3 s−1 for annihilation into bb¯ at the dark matter mass of 10 GeV, which is a factor of 3 times larger than the canonical cross section. The limits are weaker for larger dark matter masses. The limits can be improved further with more Fermi-LAT data as well as by using the power spectrum at lower multipoles (l≲150), which are currently not used due to a potential Galactic foreground contamination.
124377961
A neutrino burst and gravitational wave from supernova explosions
10036439
Polarized photons in radiative muon capture
We discuss the measurement of polarized photons arising from radiative muon capture. The spectrum of left circularly polarized photons or equivalently the circular polarization of the photons emitted in radiative muon capture on hydrogen is quite sensitive to the strength of the induced pseudoscalar coupling constant $g_P$. A measurement of either of these quantities, although very difficult, might be sufficient to resolve the present puzzle resulting from the disagreement between the theoretical prediction for $g_P$ and the results of a recent experiment. This sensitivity results from the absence of left-handed radiation from the muon line and from the fact that the leading parts of the radiation from the hadronic lines, as determined from the chiral power counting rules of heavy-baryon chiral perturbation theory, all contain pion poles.
122375456
Renormalization group analysis of nuclear current operators
A Wilsonian renormalization group (WRG) equation for nuclear current operators in two-nucleon systems is derived. Nuclear current operators relevant to low-energy Gamow-Teller transitions are analyzed using the WRG equation. We employ the axial two-body current operators from phenomenological models and heavy-baryon chiral perturbation theory, which are quite different from one another in describing small-scale physics. After reducing the model space of the operators using the WRG equation, we find that there still remains a significant model dependence at {lambda}=200 MeV, where {lambda} is the sharp cutoff specifying the size of the model space. A model-independent effective current operator is found at a rather small cutoff value, {lambda}=70 MeV. By simulating the effective current operator at {lambda}=70 MeV, we obtain a current operator based on a pionless theory, thereby arguing that an equivalence relation exists between nuclear current operators of phenomenological models and those of effective field theories.
639846
Neutrino-deuteron reactions at solar neutrino energies
Abstract In interpreting the SNO experiments, accurate estimates of the νd reaction cross sections are of great importance. We improve the previous estimates of our group by updating some of its inputs and by taking into account the results of a recent effective-field-theoretical calculation. The new cross sections are slightly (∼1%) larger than the previously reported values. It is shown to be reasonable to assign 1% uncertainty to the νd cross sections reported here; this error estimate does not include radiative corrections, for which we refer to the literature.
1475604
Low energy proton-proton scattering in effective field theory
Low energy proton-proton scattering is studied in pionless effective field theory. Employing the dimensional regularization and MS and power divergence subtraction schemes for loop calculation, we calculate the scattering amplitude in the {sup 1}S{sub 0} channel up to the next-to-next-to leading order and fix low-energy constants that appear in the amplitude by effective range parameters. We study the regularization scheme and scale dependence in the separation of the Coulomb interaction from the scattering length and effective range for the S-wave proton-proton scattering.
118906717
Leading chiral corrections to the nucleon generalized parton distributions
Using heavy baryon chiral perturbation theory we study the leading chiral corrections to the complete set of nucleon generalized parton distributions (GPDs). We compute the leading quark mass and momentum transfer dependence of the moments of nucleon GPDs through the nucleon off-forward twist-2 matrix elements. These results are then applied to get insight on the GPDs and their impact parameter space distributions.