Narrow Results

We consider in this paper a simple oscillating Quintom model of dark energy which has two free parameters and an equation of state oscillating and crossing -1. For low redshifts the equation of state of this model resembles itself similar to the linearly parametrized dark energy, however differs substantially at large redshifts. We fit our model to the observational data separately from the new high redshifts supernova observations from the HST/GOODS program and previous supernova, CMB and galaxy clustering. Our results show that because of the oscillating feature of our model the constraints from observations at large redshifts such as CMB become less stringent.

Strong magnetic fields are suspected to exist in some core-collapse supernovae, which would affect the neutrino processes such as ν_e+n ⇌ e^-+p and . We briefly review the motion of charged particles in the presence of magnetic fields and the changes of the above processes induced by magnetic fields. We also discuss the implications of these changes for supernova physics in the context of neutrino-driven explosion.

Neutrino is a tiny weakly interacting massive particle, but it has strong impacts on various cosmological and astrophysical phenomena. Neutrinos play a critical role in nucleosynthesis of light-to-heavy mass elements in core-collapse supernovae. The light element synthesis is particularly affected by neutrino oscillation (MSW) effect through the ν-process. We propose first that precise determination of sin² 2θ₁₃ and mass hierarchy can be made by a theoretical study of the observed ⁷Li/¹¹B ratio in stars and presolar grains which are produced from SN ejecta. Theoretical sensitivity in our proposed method is shown to be superior to ongoing long-baseline neutrino experiments for the parameter region 10⁻⁴ ≤ sin²2θ₁₃ ≤ 10⁻². We secondly discuss how to constrain the neutrino mass Σm_ν from precise analysis of cosmic microwave background anisotropies in the presence of primordial magnetic field. We obtain an upper limit Σm_ν < 1.3eV(2σ). Thirdly, we discuss decaying dark-matter particle model in order to solve the primordial lithium problems that the standard Big-Bang nucleosynthesis theory predicts extremely different ⁶Li and ⁷Li abundances from observations.

Nuclear physics is an indispensable input for the investigation of high energy astrophysical phenomena involving compact objects. In this paper I take a gravitational collapse of massive stars as an example and show how the macroscopic dynamics is influenced by the properties of nuclei and nuclear matter. I will discuss two topics that are rather independent of each other. The first one is the interplay of neutrino-nuclei inelastic scatterings and the standing accretion shock instability in the core of core collapse supernovae and the second is concerning the neutrino emissions from black hole formations and their dependence on the equation of state at very high densities. In the latter, I will also demonstrate that future astronomical observations might provide us with valuable information on the equation of state of hot dense matter.

We report the recent developments on the tables of equation of state for dense matter and their influence on core-collapse supernovae and associated neutrino emissions. We study the gravitational collapse of massive stars by the numerical simulations with the tables of equation of state recently developed in relativistic many body frameworks. I discuss whether the equation of state of dense matter can be probed by the properties of neutrino signals from black hole forming supernovae, being different from ordinary neutrino bursts from supernova explosions.

We investigate the momentum given to a protoneutron star, the pulsar kick, during the first ten seconds after temperature equilibrium is reached. Using a model with two sterile neutrinos obtained by fits to the MiniBooNE and LSND experiments, which is consistent with a new global fit, there is a large mixing angle, and the effective volume for emission is calculated. Using formulations with neutrinos created by URCA processes in a strong magnetic field, so the lowest Landau level has a sizable probability, we find that with known parameters, the asymmetric sterile neutrino emissivity might account for large pulsar kicks.

We calculate the momentum given to a proto-neutron star during the first 10 s after temperature equilibrium is reached, using recent evidence of sterile neutrinos and a measurement of the mixing angle. This is a continuation of an earlier estimate with a wide range of possible mixing angles. Using the new mixing angle we find that sterile neutrinos can account for the observed pulsar velocities.

As a solution to the well-known problem that the shock wave potentially responsible for the explosion of a supernova actually tends to stall, we propose a new energy source arising from our model for dark matter. Our earlier model proposed that dark matter should consist of cm-large white dwarf-like objects kept together by a skin separating two different sorts of vacua. These dark matter balls or pearls will collect in the middle of any star throughout its lifetime. At some stage during the development of a supernova, the balls will begin to take in neutrons and then other surrounding material. By passing into a ball nucleons fall through a potential of order 10 MeV, causing a severe production of heat — of order 10 foe for a solar mass of material eaten by the balls. The temperature in the iron core will thereby be raised, splitting up the iron into smaller nuclei. This provides a mechanism for reviving the shock wave when it arrives and making the supernova explosion really occur. The onset of the heating due to the dark matter balls would at first stop the collapse of the supernova progenitor. This opens up the possibility of there being two collapses giving two neutrino outbursts, as apparently seen in the supernova SN1987A — one in Mont Blanc and one 4 h 43 min later in both IMB and Kamiokande.

The spectral energy distribution (SED) sequence for type Ia supernovae (SN Ia) is modeled by an artificial neural network. The SN Ia luminosity is characterized as a function of phase, wavelength, a color parameter and a decline rate parameter. After training and testing the neural network, the SED sequence could give both the spectrum with wavelength range from 3000 Åto 8000 Åand the light curve with phase from 20 days before to 50 days after the maximum luminosity for the supernovae with different colors and decline rates. Therefore, we call this the Artificial Neural Network Spectral Light Curve Template (ANNSLCT) model. We retrain the Joint Light-curve Analysis (JLA) supernova sample by using the ANNSLCT model and obtain the parameters for each supernova to make a constraint on the cosmological $\mathrm{\Lambda }$CDM model. We find that the best fitting values of these parameters are very close to those from the JLA sample trained with the Spectral Adaptive Lightcurve Template 2 (SALT2) model. It is expectable that the ANNSLCT model has potential to analyze more SN Ia multi-color light curves measured in future observation projects.

In this paper the formulae of magnetic susceptibility (MS) of charged particles are deduced in nonrelativistic and relativistic mean-field approximations in bulk matter. The analytic relativistic expression at high densities and strong fields, deduced for the de Hass–van Alphen (HVA) oscillation, shows that the oscillation frequency is proportional to the square of chemical potential and the reciprocal of the field, and is independent of the temperature. Numerical calculations are performed at finite temperatures and in a field range where the equation of state is not sensitive to the field. The nonoscillatory MS of the protoneutron star, which is dominated by the contributions of electrons (and light quarks, if deconfined) and is almost independent of the field, decreases as the protoneutron matter becomes denser. The numerical results for the HVA oscillation are also given. The oscillation amplitude becomes larger as the star becomes colder. We find that superposition of the HVA oscillations changes the oscillation properties drastically if the color deconfinement occurs at high densities.

Qualitative analysis of additional energy of neutrino and antineutrino in plasma is performed. A general expression for the neutrino self-energy operator is obtained in the case of ultra-high energies when the local limit of the weak interaction is not valid. The neutrino and antineutrino additional energy in plasma is calculated using the dependence of the W- and Z-boson propagators on the momentum transferred. The kinematical region for the neutrino radiative transition (the so-called "neutrino spin light") is established for some important astrophysical cases. For high energy neutrino and antineutrino, dominating transition channels in plasma, ν_e + e⁺ → W⁺, and , are indicated.

We review the recent progress in understanding the nature of gamma-ray bursts (GRBs). The occurrence of GRB is explained by the Induced Gravitational Collapse (IGC) in FeCO Core–Neutron star binaries and Neutron star–Neutron star binary mergers, both processes occur within binary system progenitors. Making use of this most unexpected new paradigm, with the fundamental implications by the neutron star (NS) critical mass, we find that different initial configurations of binary systems lead to different GRB families with specific new physical predictions confirmed by observations.

We discuss observable aspects of neutron stars and supernova that are influenced by the properties of matter at extreme density. In particular, we explore the possible role phase transitions to quark matter phases at supra nuclear density. The competition between the strange quark mass and the pairing energy in quark matter, and show that it leads to a rich phase structure at densities of relevance to neutron stars. The equation of state and transport properties of quark matter is shown to be strongly influenced by pairing correlations at the Fermi surface.

During the core bounce of a supernova collapse resonant active-to-active (ν_a→ν_a), as well as active-to-sterile (ν_a→ν_s) neutrino (ν) oscillations can take place. Besides, over this phase weak magnetism increases antineutrino mean free paths, and thus its luminosity. Because the oscillation feeds mass-energy into the target ν species, the large mass-squared difference between species (ν_a→ν_s) implies a huge amount of power to be given off as gravitational waves (L_GWs~10⁴⁹ergs^-1), due to anisotropic but coherent ν flow over the oscillation length. This anisotropy in the ν-flux is driven by both the universal spin-rotation and the spin-magnetic coupling. The new spacetime strain estimated this way is still several orders of magnitude larger than those from ν diffusion (convection and cooling) or quadrupole moments of the neutron star matter. This new feature turns these bursts the more promising supernova gravitational-wave signal that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.

The decreasing of the inertial mass density, established in the past for dissipative fluids, is found to be produced by the "inertial" term of the transport equation. Once the transport equation is coupled to the dynamical equation, one finds that the contribution of the inertial term diminishes the effective inertial mass and the "gravitational" force term, by the same factor. An intuitive picture and prospective applications of this result to astrophysical scenarios are discussed.

Artificial viscosity is widely used in numerical calculations of stellar core collapse. The failure or success of the prompt mechanism explosion of type-II supernovae is strongly dependent on the numerical code, and the study of a suitable and efficient method of capturing the shock front is a current problem. We present a novel one-term artificial viscosity which is dependent on the velocity field along the shock front. We show that this form of artificial viscosity is able to capture the profile of a plane shock wave, removing the non-physical oscillations originated by the artificial viscosity of von Neumann and Richtmyer type.

It has been known since 1987 that many features of supernovae cannot be described by the spherically-symmetric picture assumed in one-dimensional explosion models. However, the study of the propagation of a supernova shock through a star in more than one spatial dimension is still in its infancy. Understanding this propagation, and the mixing associated with it, is critical for determining accurate supernova yields and correctly interpreting observations based on those yields — from gamma-rays and overall light curves produced in supernova explosions to the abundances of isotopes studied in stars. Here we review the current state-of-the-art in this field. By necessity, this problem is computational and therefore provides an ideal setting to discuss how verification and validation techniques can play an important role in taking full advantage of the results from numerical simulations. We discuss this problem using the full arsenal of verification and validation techniques currently available.

We provide an equation of state for high density supernova matter by applying a momentum-dependent effective interaction. We focus on the study of the equation of state of high density and high temperature nuclear matter containing leptons (electrons and neutrinos) under the chemical equilibrium condition. The conditions of charge neutrality and equilibrium under the β-decay process lead first to the evaluation of the lepton fractions and afterward to the evaluation of internal energy, pressure, entropy and, in total to the equation of state of hot nuclear matter for various isothermal cases. Thermal effects on the properties and equation of state of nuclear matter are evaluated and analyzed in the framework of the proposed effective interaction model. Since supernova matter is characterized by a constant entropy, we also present the thermodynamic properties for the isentropic case. Special attention is devoted to the study of the contribution of the components of β-stable nuclear matter to the entropy per particle, a quantity of great interest for the study of structure and collapse of supernovas.

Although there is a general understanding of the core collapse supernovae, a definitive microscopic model is still to come. We discuss the usefulness of neutrino observations. We analyze the SN1987A observations of Kamiokande-II, IMB and Baksan and show that they provide a 2.5σ support to the standard scenario for the explosion. In this context, we discuss the neutrinos as trigger for the search of the gravity wave impulsive emission. We bound the neutrino mass using the SN1987A data and argue, using simulated data, that a future galactic supernova could probe the sub-eV region.

We review recent progress in our understanding of the nature of Gamma Ray Bursts (GRBs) and in particular, of the relationship between short GRBs and long GRBs. The first example of a short GRB is described. The coincidental occurrence of a GRB with a supernova (SN) is explained within the induced gravitational collapse (IGC) paradigm, following the sequence: (1) an initial binary system consists of a compact carbon–oxygen (CO) core star and a neutron star (NS); (2) the CO core explodes as a SN, and part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a black hole (BH) giving rise to a GRB; (3) a new NS is generated by the SN as a remnant. The observational consequences of this scenario are outlined.