A simple analytic model for astrophysical S-factors

We propose a physically transparent analytic model of astrophysical S-factors as a function of a center-of-mass energy E of colliding nuclei (below and above the Coulomb barrier) for non-resonant fusion reactions. For any given reaction, the S(E)-model contains four parameters [two of which approximate the barrier potential, U(r)]. They are easily interpolated along many reactions involving isotopes of the same elements; they give accurate practical expressions for S(E) with only several input parameters for many reactions. The model reproduces the suppression of S(E) at low energies (of astrophysical importance) due to the shape of the low-r wing of U(r). The model can be used to reconstruct U(r) from computed or measured S(E). For illustration, we parameterize our recent calculations of S(E) (using the Sao Paulo potential and the barrier penetration formalism) for 946 reactions involving stable and unstable isotopes of C, O, Ne, and Mg (with 9 parameters for all reactions involving many isotopes of the same elements, e.g., C+O). In addition, we analyze astrophysically important 12C+12C reaction, compare theoretical models with experimental data, and discuss the problem of interpolating reliably known S(E) values to low energies (E <= 2-3 MeV).Comment: 13 pages, 5 figures, Phys. Rev. C, accepte

Optical control of electron spin coherence in CdTe/(Cd,Mg)Te quantum wells

Optical control of the spin coherence of quantum well electrons by short laser pulses with circular or linear polarization is studied experimentally and theoretically. For that purpose the coherent electron spin dynamics in a n-doped CdTe/(Cd,Mg)Te quantum well structure was measured by time-resolved pump-probe Kerr rotation, using resonant excitation of the negatively charged exciton (trion) state. The amplitude and phase shifts of the electron spin beat signal in an external magnetic field, that are induced by laser control pulses, depend on the pump-control delay and polarization of the control relative to the pump pulse. Additive and non-additive contributions to pump-induced signal due to the control are isolated experimentally. These contributions can be well described in the framework of a two-level model for the optical excitation of the resident electron to the trion.Comment: 15 pages, 18 figure

Thermal X-Ray Pulses Resulting From Pulsar Glitches

The non-spherically symmetric transport equations and exact thermal evolution model are used to calculate the transient thermal response to pulsars. The three possible ways of energy release originated from glitches, namely the `shell', `ring' and `spot' cases are compared. The X-ray light curves resulting from the thermal response to the glitches are calculated. Only the `spot' case and the `ring' case are considered because the `shell' case does not produce significant modulative X-rays. The magnetic field ($\vec B$) effect, the relativistic light bending effect and the rotational effect on the photons being emitted in a finite region are considered. Various sets of parameters result in different evolution patterns of light curves. We find that this modulated thermal X-ray radiation resulting from glitches may provide some useful constraints on glitch models.Comment: 48 pages, 20 figures, submitted to Ap

Neutrino emission in neutron matter from magnetic moment interactions

Neutrino emission drives neutron star cooling for the first several hundreds of years after its birth. Given the low energy ($\sim$ keV) nature of this process, one expects very few nonstandard particle physics contributions which could affect this rate. Requiring that any new physics contributions involve light degrees of freedom, one of the likely candidates which can affect the cooling process would be a nonzero magnetic moment for the neutrino. To illustrate, we compute the emission rate for neutrino pair bremsstrahlung in neutron-neutron scattering through photon-neutrino magnetic moment coupling. We also present analogous differential rates for neutrino scattering off nucleons and electrons that determine neutrino opacities in supernovae. Employing current upper bounds from collider experiments on the tau magnetic moment, we find that the neutrino emission rate can exceed the rate through neutral current electroweak interaction by a factor two, signalling the importance of new particle physics input to a standard calculation of relevance to neutron star cooling. However, astrophysical bounds on the neutrino magnetic moment imply smaller effects.Comment: 9 pages, 1 figur

Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots

The problem of how single "central" spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying timescales and dynamical responses (exponential, power-law, Gaussian, etc). Here we detect the small random fluctuations of central spins in thermal equilibrium (holes in singly-charged (In,Ga)As quantum dots) to reveal the timescales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at zero magnetic field, that increase to $\sim$5 $\mu$s as hole-nuclear coupling is suppressed with small (100 G) applied fields. Concomitantly, the noise lineshape evolves from Lorentzian to power-law, indicating a crossover from exponential to inverse-log dynamics.Comment: 4 pages & 4 figures, + 8 pages supplemental materia