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.
118449544
Spin Observables in the Two-Nucleon Capture and Dissociation Processes at Low Energies
Spin observables in radiative neutron capture on a proton and its inverse process, photodisintegration of the deuteron are calculated using a pionless effective field theory with di-baryon fields. Good agreement with the results of existing standard nuclear physics approach (SNPA) is obtained at very low energies. As energy increases, however, the discrepancy between the effective field theory and the SNPA becomes substantial. We discuss the origin of the difference.
14652153
Neutron–neutron fusion
Abstract The neutron–neutron fusion process, n n → d e ν , at very low neutron energies is studied in the framework of pionless effective field theory that incorporates dibaryon fields. The cross section and electron energy spectrum for this process are calculated up to next-to-leading order. We include the radiative corrections of O ( α ) calculated for the one-body transition amplitude. The precision of our theoretical estimates is found to be governed essentially by the accuracy with which the empirical values of the neutron–neutron scattering length and effective range are currently known. Also discussed is the precision of theoretical estimates of the transition rates of related electroweak processes in few-nucleon systems.
55936228
Effective field theory of 3He
We examine the effects of the long range Coulomb force on the three-body contact interaction in a pionless effective theory of 3He. The corresponding interaction in 3H exhibits limit-cycle behavior and we show that this is not altered by the 1/r singularity of the potential.
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.
118594879
Renormalization-group analysis for low-energy scattering of charged particles
The low-energy scattering of two charged particles is analyzed using a renormalization group approach based on dimensional regularization with power-divergence subtraction. A nontrivial solution with a marginally unstable direction is found, corresponding to a system with a bound state at zero energy. For purely energy-dependent perturbations around this solution, the power counting agrees with that from Wilsonian methods. These terms in the effective potential are in direct correspondence with the the terms in the Coulomb-distorted effective-range expansion. We also study perturbations that depend on off-shell momenta as well as energy, and we show that these affect only the off-shell form of the scattering matrix. These terms are of higher order than the corresponding energy-dependent ones and so terms in the potential that depend only on the off-shell momenta do not have definite orders in power counting.
119042532
Appearance of neutronization peak and decaying supernova neutrinos
Nonradiative neutrino decay, which is not satisfactorily constrained, possibly and significantly changes the detected neutrino signal from galactic supernova explosions. We focus on the appearance of a sharp peak due to a neutronization burst in the time profile; this phenomenon would occur if the original \nu_e, produced at the neutrinosphere and becoming \nu_{2,3} at the stellar surface, decays into a lighter antineutrino state such as \bar\nu_{1,2} coupled to \bar\nu_e. This is due to the fact that the signature of the neutronization burst is common to all numerical simulations. Therefore, the appearance of a neutronization peak in the \bar\nu_e signal, if it were detected, would clearly indicate the nonstandard properties of neutrinos. Using a newly developed formulation that includes flavor conversions inside the supernova envelope and neutrino decay during propagation in a vacuum, we calculate the expected neutrino signal at the detectors; the lifetimes of three modes \tau_{12}, \tau_{13}, and \tau_{23} are taken to be free parameters. We further introduce simple quantities, which represent a peak sharpness of time profile and spectral hardness, and investigate the parameter dependence of these quantities. As the result, it is found that they are quite dependent on the relevant parameters, but it would be quite difficult to distinguish models using the signal obtained by the Super-Kamiokande detector; the future megaton-class detectors would have sufficient sensitivity. We also compare the neutrino decay model with another mechanism, i.e., resonant spin-flavor conversion, which also may give the appearance of a neutronization peak, and conclude that these two independent mechanisms give a different signal and one can be distinguished from the other.
15665946
Cosmic Star Formation History and the Future Observation of Supernova Relic Neutrinos
We investigate the flux and event rate of supernova relic neutrinos (SRNs) and discuss their implications for the cosmic star formation rate. Since SRNs are diffuse neutrino background emitted from past core-collapse supernova explosions, they contain fruitful information on the supernova rate in the past and present universe, as well as on the supernova neutrino spectrum itself. As reference models, we adopt the supernova rate model based on recent observations and the supernova neutrino spectrum numerically calculated by several groups. In the detection energy range Ee > 10 MeV, which will possibly be a background-free region in the near future, the SRN event rate is found to be 1-2 yr-1 at a water Cerenkov detector with a fiducial volume of 22.5 kton, depending on the adopted neutrino spectrum. We also simulate the expected signal with one set of the reference models by using the Monte Carlo method and then analyze these pseudodata with several free parameters, obtaining the distribution of the best-fit values for them. In particular, we use a parameterization such that RSN(z) = R(1 + z)α, where RSN(z) is the comoving supernova rate density at redshift z and R and α are free parameters, assuming that the supernova neutrino spectrum and luminosity are well understood by way of a future Galactic supernova neutrino burst or the future development of numerical supernova simulations. The obtained 1 σ errors for these two parameters are found to be δα/α = 30% (7.8%) and δR/R = 28% (7.7%) for a detector with an effective volume of 22.5 kton × 5 yr (440 kton × 5 yr), where one of the parameters is fixed. On the other hand, if we fix neither of the values for these two parameters, the expected errors become rather large, δα/α = 37% and δR/R = 55%, even with an effective volume of 440 kton × 5 yr.
118855488
Gamma-ray background anisotropy from Galactic dark matter substructure
Dark matter annihilation in Galactic substructure will imprint characteristic angular signatures on the all-sky map of the diffuse gamma-ray background. We study the gamma-ray background anisotropy due to the subhalos and discuss detectability at the Fermi Gamma-ray Space Telescope. In contrast to earlier work that relies on simulated all-sky maps, we derive analytic formulae that enable to directly compute the angular power spectrum, given parameters of subhalos such as mass function, and radial profile of gamma-ray luminosity. As our fiducial subhalo models, we adopt M^(-1.9) mass spectrum, subhalos radial distribution suppressed toward the Galactic center, and luminosity profile of each subhalo dominated by its smooth component. We find that, for multipole regime corresponding to theta<~5°, the angular power spectrum is dominated by a noiselike term, with suppression due to internal structure of relevant subhalos. If the mass spectrum extends down to Earth-mass scale, then the subhalos would be detected in the anisotropy with Fermi at angular scales of ~10°, if their contribution to the gamma-ray background is larger than ~20%. If the minimum mass is around 10^4M[sun], on the other hand, the relevant angular scale for detection is ~1°, and the anisotropy detection requires that the subhalo contribution to the gamma-ray background intensity is only ~4%. These can be achieved with a modest boost for particle-physics parameters. We also find that the anisotropy analysis could be a more sensitive probe for the subhalos than individual detection. We also study dependence on model parameters, where we reach the similar conclusions for all the models investigated. The analytic approach should be very useful when Fermi data are analyzed, and the obtained angular power spectrum is interpreted in terms of subhalo models.
119396432
Resonant spin flavor conversion of supernova neutrinos: Dependence on presupernova models and future prospects
We study the resonant spin-flavor (RSF) conversion of supernova neutrinos, which is induced by the interaction between the nonzero neutrino magnetic moment and the supernova magnetic fields, and its dependence on presupernova models. As the presupernova models, we adopt the latest ones by Woosley, Heger, and Weaver, and, further, models with both solar and zero metallicity are investigated. Since the $(1\ensuremath{-}{2Y}_{e})$ profile of the new presupernova models, which is responsible for the RSF conversion, suddenly drops at the resonance region, the completely adiabatic RSF conversion is not realized, even if ${\ensuremath{\mu}}_{\ensuremath{\nu}}{B}_{0}{=(10}^{\ensuremath{-}12}{\ensuremath{\mu}}_{B}{)(10}^{10}\mathrm{G}),$ where ${B}_{0}$ is the strength of the magnetic field at the surface of the iron core. In particular for the model with zero metallicity, the conversion is highly nonadiabatic in the high energy region, reflecting the $(1\ensuremath{-}{2Y}_{e})$ profile of the model. In calculating the flavor conversion, we find that the shock wave propagation, which changes density profiles drastically, is a much more severe problem than it is for the pure Mikheyev-Smirnov-Wolfenstein (MSW) conversion case. This is because the RSF effect occurs at a far deeper region than the MSW effect. To avoid the uncertainty concerning the shock propagation, we restrict our discussion to 0.5 s after the core bounce (and for more conservative discussion, 0.25 s), during which the shock wave is not expected to affect the RSF region. We also evaluate the energy spectrum at the Super-Kamiokande detector for various models using the calculated conversion probabilities, and find that it is very difficult to obtain useful information on the supernova metallicities and magnetic fields or on the neutrino magnetic moment from the supernova neutrino observation. Future prospects are also discussed.
125796612
Klein-Nishina effects on Synchrotron and Synchrotron self-Compton spectrum