16888286
The fate of a neutron star just below the minimum mass: does it explode?
First results of numerical simulations are presented which compute the dynamical evolution of a neutron star with a mass slightly below the minimum stable mass by means of a new implicit (general relativistic) hydrodynamic code. We show that such a star first undergoes a phase of quasi-static expansion, caused by slow nuclear -decays, lasting for about 20 seconds, but then explodes violently. The kinetic energy of the explosion is around10 49 erg, the peak luminosity in electron anti-neutrinos is of order 10 52 erg/s, and the thermodynamic conditions of the expanding matter are favorable for r-process nucleosynthesis. These results are obtained for the Harrison-Wheeler equation of state and a simple and, possibly, unrealistic treatment of - decay rates and nuclear fission, which were adopted for compar- ison with previous works. However, we do not expect that the outcome will change qualitatively if more recent nuclear input physics is used. Although our study does not rely on a specific scenario of how a neutron star starting from a bigger (and stable) mass can reach the dynamical phase, we implicitly assume that the final mass-loss event happens on a very short time scale, i.e., on a time scale shorter than a sound-crossing time, by removing a certain amount of mass as an initial perturbation. This assumption im- plies that the star has no time to adjust its nuclear composition to the new mass through a sequence of quasi-equilibria. In the lat- ter case, however, there exists no stable configuration below the minimum mass, because the equation of state of fully catalyzed matter is too soft. Therefore, the dynamics of the explosion will not be too different from what we have obtained if different initial perturbations are assumed.
118715119
EFFECTS OF RESISTIVITY ON MAGNETIZED CORE-COLLAPSE SUPERNOVAE
We studied the role of turbulent resistivity in the core-collapse of a strongly magnetized massive star, carrying out two-dimensional resistive-MHD simulations. Three cases with different initial strengths of magnetic field and rotation are investigated: (1) a strongly magnetized rotating core, (2) a moderately magnetized rotating core, and (3) a very strongly magnetized non-rotating core. In each case, one ideal-MHD model and two resistive-MHD models are computed. As a result of these computations, each model shows an eruption of matter assisted by magnetic acceleration (and also by centrifugal acceleration in the rotating cases). We found that resistivity attenuates the explosion in cases 1 and 2, while it enhances the explosion in case 3. We also found that in the rotating cases, the main mechanisms for the amplification of a magnetic field in the post-bounce phase are an outward advection of the magnetic field and a twisting of poloidal magnetic field lines by differential rotation, which are somewhat dampened down with the presence of resistivity. Although magnetorotational instability seems to occur in the rotating models, it plays only a minor role in magnetic field amplification. Another impact of resistivity is that on the aspect ratio. In the rotating cases, a large aspect ratio of the ejected matter, >2.5, attained in an ideal-MHD model is reduced to some extent in a resistive model. These results indicate that resistivity possibly plays an important role in the dynamics of strongly magnetized supernovae.
119251795
Global Simulations of Magnetorotational Instability in the Collapsed Core of a Massive Star
We performed the first global numerical simulations of magnetorotational instability from a sub-magnetar-class seed magnetic field in core-collapse supernovae. As a result of axisymmetric ideal MHD simulations, we found that the magnetic field is greatly amplified to magnetar-class strength. In the saturation phase, a substantial part of the core is dominated by turbulence, and the magnetic field possesses dominant large-scale components, comparable to the size of a proto-neutron star. A pattern of coherent channel flows, which generally appears during the exponential growth phase in previous local simulations, is not observed in our global simulations. While the approximate convergence in the exponential growth rate is attained by increasing spatial resolution, that of the saturation magnetic field is not achieved due to still large numerical diffusion. Although the effect of the magnetic field on the dynamics is found to be mild, a simulation with a high enough resolution might result in a larger impact.
118908804
Multigroup simulation of protoneutron star cooling and neutrino spectra
122249200
Constraining neutrino oscillation parameters with future observations of supernova neutrinos by various types of detectors
We evaluate the potential for constraining neutrino oscillation parameters with future observations of supernova neutrinos. For some selected oscillation parameters, we calculate the expected energy spectra and angular distributions of neutrino events in various detectors (Super-Kamiokande, ICARUS, KamLAND and IceCube) for an assumed galactic core-collapse supernova. We investigate to what extent the oscillation parameters could be constrained using χ2 analysis when the expected events are really observed.
122604041
NEUTRINOS FROM PROTONEUTRON STARS
We performed numerical simulations of the quasistatic evolution of protoneutron star with neutrino transfer using multigroup flux limited diffusion scheme. The second half of the supernova neutrinos are emitted in this stage. We found 1) the flux decays rapidly and its mean energy falls below j/e's mean energy at the late stage, 2) Pe's carry out energy of about 24% of the total energy emitted in this cooling phase, and 3) the time-integrated energy spectra of u^s and v^s can be roughly fitted by the Fermi-Dirac spectra with positive chemical potentials while those of the other neutrinos can be fitted by MaxwellBoltzmann spectra. These results suggest that the total energy of the neutrino burst from SN1987A was overestimated if one assumed that the Pe's spectrum is the Fermi-Dirac one with a vanishing chemical potential and that all species of neutrinos contribute equally.
119699626
SUSY breaking by nonperturbative dynamics in a matrix model for 2D type IIA superstrings
Abstract We explicitly compute nonperturbative effects in a supersymmetric double-well matrix model corresponding to two-dimensional type IIA superstring theory on a nontrivial Ramond–Ramond background. We analytically determine the full one-instanton contribution to the free energy and one-point function, including all perturbative fluctuations around the one-instanton background. The leading order two-instanton contribution is determined as well. We see that supersymmetry is spontaneously broken by instantons, and that the breaking persists after taking a double scaling limit which realizes the type IIA theory from the matrix model. The result implies that spontaneous supersymmetry breaking occurs by nonperturbative dynamics in the target space of the IIA theory. Furthermore, we numerically determine the full nonperturbative effects by recursive evaluation of orthogonal polynomials. The free energy of the matrix model appears well-defined and finite even in the strongly coupled limit of the corresponding type IIA theory. The result might suggest a weakly coupled theory appearing as an S-dual to the two-dimensional type IIA superstring theory.
17171161
Observing dynamical supersymmetry breaking with euclidean lattice simulations
A strict positivity of the ground-state energy is a necessary and sufficient condition for spontaneous supersymmetry breaking. This ground-state energy may be directly determined from the expectation value of the Hamiltonian in the functional integral, defined with an antiperiodic temporal boundary condition for all fermionic variables. We propose to use this fact to observe the dynamical spontaneous supersymmetry breaking in Euclidean lattice simulations. If a lattice formulation possesses a manifestly preserved fermionic symmetry, there exists a natural choice of a Hamiltonian operator that is consistent with a topological nature of the Witten index. We numerically confirm the validity of our idea in models of supersymmetric quantum mechanics. We further examine the possibility of dynamical supersymmetry breaking in the two-dimensional N =( 2, 2) super Yang-Mills theory with the gauge group SU(2), for which the Witten index is unknown. Although statistical errors are still large, we do not observe positive ground-state energy, at least within one standard deviation. This prompts us to draw a different conclusion from a recent conjectural claim that supersymmetry is dynamically broken in this system.
13427982
Quantum bubble nucleation beyond WKB: Resummation of vacuum bubble diagrams
On the basis of Borel resummation, we propose a systematical improvement of the bounce calculus of the quantum bubble nucleation rate. We study a metastable super-renormalizable field theory, $D$-dimensional, $O(N)$ symmetric ${\ensuremath{\varphi}}^{4}$ model $(Dl4)$ with an attractive interaction. The validity of our proposal is tested in $D=1$ (quantum mechanics) by using the perturbation series of ground state energy to high orders. We also present a result in $D=2,$ based on an explicit calculation of vacuum bubble diagrams to five loop orders.
119251656
Large-N limit of the gradient flow in the 2D O(N) nonlinear sigma model
The gradient flow equation in the 2D $O(N)$ nonlinear sigma model with lattice regularization is solved in the leading order of the $1/N$ expansion. By using this solution, we analytically compute the thermal expectation value of a lattice energy--momentum tensor defined through the gradient flow. The expectation value reproduces thermodynamic quantities obtained by the standard large-$N$ method. This analysis confirms that the above lattice energy--momentum tensor restores the correct normalization automatically in the continuum limit, in a system with a non-perturbative mass gap.
118328576
Application of Noncommutative Geometry on Discrete Space to Anomaly