Dispersive effects in neutron matter superfluidity

The explicit energy dependence of the single particle self-energy (dispersive effects), due to short range correlations, is included in the treatment of neutron matter superfluidity. The method can be applied in general to strong interacting fermion systems, and it is expected to be valid whenever the pairing gap is substantially smaller than the Fermi kinetic energy. The results for neutron matter show that dispersive effects are strong in the density region near the gap closure.Comment: 9 pages, 4 ps figure

Chaos vs. Linear Instability in the Vlasov Equation: A Fractal Analysis Characterization

In this work we discuss the most recent results concerning the Vlasov dynamics inside the spinodal region. The chaotic behaviour which follows an initial regular evolution is characterized through the calculation of the fractal dimension of the distribution of the final modes excited. The ambiguous role of the largest Lyapunov exponent for unstable systems is also critically reviewed.Comment: 10 pages, RevTeX, 4 figures not included but available upon reques

Single particle spectrum and binding energy of nuclear matter

In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a parabolic approximation is often used in the literature. The variation in the binding energy value introduced by the parabolic approximation is quantitatively analyzed in detail. It is found that the approximation can introduce an uncertainty of 1-2 MeV near the saturation density.Comment: 6 Latex pages, 3 postscript figure

An ab initio theory of double odd-even mass differences in nuclei

Two aspects of the problem of evaluating double odd-even mass differences D_2 in semi-magic nuclei are studied related to existence of two components with different properties, a superfluid nuclear subsystem and a non-superfluid one. For the superfluid subsystem, the difference D_2 is approximately equal to 2\Delta, the gap \Delta being the solution of the gap equation. For the non-superfluid subsystem, D_2 is found by solving the equation for two-particle Green function for normal systems. Both equations under consideration contain the same effective pairing interaction. For the latter, the semi-microscopic model is used in which the main term calculated from the first principles is supplemented with a small phenomenological addendum containing one phenomenological parameter supposed to be universal for all medium and heavy atomic nuclei.Comment: 7 pages, 10 figures, Report at Nuclear Structure and Related Topics, Dubna, Russia, July 2 - July 7, 201

Measuring neutron-star properties via gravitational waves from binary mergers

We demonstrate by a large set of merger simulations for symmetric binary neutron stars (NSs) that there is a tight correlation between the frequency peak of the postmerger gravitational-wave (GW) emission and the physical properties of the nuclear equation of state (EoS), e.g. expressed by the radius of the maximum-mass Tolman-Oppenheimer-Volkhoff configuration. Therefore, a single measurement of the peak frequency of the postmerger GW signal will constrain the NS EoS significantly. For plausible optimistic merger-rate estimates a corresponding detection with Advanced LIGO is likely to happen within an operation time of roughly a year.Comment: 5 pages, 4 figures, accepted by Phys. Rev. Lett., revised version including referee comment

The neutron star in Cassiopeia A: equation of state, superfluidity, and Joule heating

The thermomagnetic evolution of the young neutron star in Cassiopea A is studied by considering fast neutrino emission processes. In particular, we consider neutron star models obtained from the equation of state computed in the framework of the Brueckner-Bethe-Goldstone many-body theory and variational methods, and models obtained with the Akmal-Pandharipande-Ravenhall equation of state. It is shown that it is possible to explain a fast cooling regime as the one observed in the neutron star in Cassiopea A if the Joule heating produced by dissipation of the small-scale magnetic field in the crust is taken into account. We thus argue that it is difficult to put severe constraints on the superfluid gap if the Joule heating is considered.Comment: 4 pages, 2 figures, to appear on A&A Letter

Chaoticity and Dissipation of Nuclear Collective Motion in a Classical Model

We analyze the behavior of a gas of classical particles moving in a two-dimensional "nuclear" billiard whose multipole-deformed walls undergo periodic shape oscillations. We demonstrate that a single particle Hamiltonian containing coupling terms between the particles' motion and the collective coordinate induces a chaotic dynamics for any multipolarity, independently on the geometry of the billiard. The absence of coupling terms allows us to recover qualitatively the "wall formula" predictions. We also discuss the dissipative behavior of the wall motion and its relation with the order-to-chaos transition in the dynamics of the microscopic degrees of freedom.Comment: LateX, 11 pages, 7 figures available on request, to appear in the Proceedings of XXXIV Winter Meeting on Nuclear Physics, Bormio 22-27 January, 199

Multiphonon emission model of spin-dependent exciton formation in organic semiconductors

The maximum efficiency in organic light-emitting diodes (OLEDs) depends on the ratio, $r=k_S/k_T$, where $k_S$ ($k_T$) is the singlet (triplet) exciton formation rate. Several recent experiments found that r increases with increasing oligomer length from a value $r \approx 1$ in monomers and short oligomers. Here, we model exciton formation as a multi-phonon emission process. Our model is based on two assertions: (i) More phonons are emitted in triplet formation than in singlet formation. (ii) The Huang-Rhys parameter for this phonon emission is smaller in long oligomers than in short ones. We justify these assertions based on recent experimental and theoretical data.Comment: 8 pages, 7 figure