Hydrodynamics of Binary Coalescence.I. Polytropes with Stiff Equations of State

We have performed a series of three-dimensional hydrodynamic calculations of binary coalescence using the smoothed particle hydrodynamics (SPH) method. The initial conditions are exact polytropic equilibrium configurations with \gam > 5/3, on the verge of dynamical instability. We calculate the emission of gravitational radiation in the quadrupole approximation. The fully nonlinear development of the instability is followed until a new equilibrium configuration is reached. We find that the properties of this final configuration depend sensitively on both the compressibility and mass ratio. An {\em axisymmetric} merged configuration is always produced when \gam\lo2.3. As a consequence, the emission of gravitational radiation shuts off abruptly right after the onset of dynamical instability. In contrast, {\em triaxial\/} merged configurations are obtained when \gam\go2.3, and the system continues to emit gravitational waves after the final coalescence. Systems with mass ratios $q\ne1$ typically become dynamically unstable before the onset of mass transfer. Stable mass transfer from one neutron star to another in a close binary is therefore probably ruled out. The maximum amplitude $h_{max}$ and peak luminosity $L_{max}$ of the gravitational waves emitted during the final coalescence are nearly independent of \gam, but depend very sensitively on the mass ratio $q$.Comment: 27 pages, uuencoded compressed postscript, 16 figures upon request from [email protected], IAS-AST-94-

The Equation of State of Dense Matter : from Nuclear Collisions to Neutron Stars

The Equation of State (EoS) of dense matter represents a central issue in the study of compact astrophysical objects and heavy ion reactions at intermediate and relativistic energies. We have derived a nuclear EoS with nucleons and hyperons within the Brueckner-Hartree-Fock approach, and joined it with quark matter EoS. For that, we have employed the MIT bag model, as well as the Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and found that the NS maximum masses are not larger than 1.7 solar masses. A comparison with available data supports the idea that dense matter EoS should be soft at low density and quite stiff at high density.Comment: 8 pages, 5 figures, invited talk given at NPA3, Dresden, March 200

Coherent open-loop optimal control of light-harvesting dynamics

We apply theoretically open-loop quantum optimal control techniques to provide methods for the verification of various quantum coherent transport mechanisms in natural and artificial light-harvesting complexes under realistic experimental constraints. We demonstrate that optimally shaped laser pulses allow to faithfully prepare the photosystem in specified initial states (such as localized excitation or coherent superposition, i.e. propagating and non-propagating states) and to probe efficiently the dynamics. These results provide a path towards the discrimination of the different transport pathways and to the characterization of environmental properties, enhancing our understanding of the role that coherent processes may play in biological complexes.Comment: 12 pages, 15 figure

Coarse Graining RNA Nanostructures for Molecular Dynamics Simulations

A series of coarse-grained models have been developed for the study of the molecular dynamics of RNA nanostructures. The models in the series have one to three beads per nucleotide and include different amounts of detailed structural information. Such a treatment allows us to reach, for the systems of thousands of nucleotides, a time scale of microseconds (i.e. by three orders of magnitude longer than in the full atomistic modelling) and thus to enable simulations of large RNA polymers in the context of bionanotechnology. We find that the 3-beads-per-nucleotide models, described by a set of just a few universal parameters, are able to describe different RNA conformations and are comparable in structural precision to the models where detailed values of the backbone P-C4' dihedrals taken from a reference structure are included. These findings are discussed in the context of the RNA conformation classes

Astrophysical constraints on the confining models : the Field Correlator Method

We explore the relevance of confinement in quark matter models for the possible quark core of neutron stars. For the quark phase, we adopt the equation of state (EoS) derived with the Field Correlator Method, extended to the zero temperature limit. For the hadronic phase, we use the microscopic Brueckner-Hartree-Fock many-body theory. We find that the currently adopted value of the gluon condensate $G_2 \simeq 0.006-0.007 \rm {GeV^4}$, which gives a critical temperature $T_c \simeq 170 \rm MeV$, produces maximum masses which are only marginally consistent with the observational limit, while larger masses are possible if the gluon condensate is increased.Comment: 7 pages, 5 figure

Structure of hybrid protoneutron stars within the Nambu--Jona-Lasinio model

We investigate the structure of protoneutron stars (PNS) formed by hadronic and quark matter in $\beta$-equilibrium described by appropriate equations of state (EOS). For the hadronic matter, we use a finite temperature EOS based on the Brueckner-Bethe-Goldstone many-body theory, with realistic two- and three-body forces. For the quark sector, we employ the Nambu--Jona-Lasinio model. We find that the maximum allowed masses are comprised in a narrow range around 1.8 solar masses, with a slight dependence on the temperature. Metastable hybrid protoneutron stars are not found.Comment: 7 pages, 6 figures, revised version accepted for publication in Phys. Rev.

The Born and Lens-Lens Corrections to Weak Gravitational Lensing Angular Power Spectra

We revisit the estimation of higher order corrections to the angular power spectra of weak gravitational lensing. Extending a previous calculation of Cooray and Hu, we find two additional terms to the fourth order in potential perturbations of large-scale structure corresponding to corrections associated with the Born approximation and the neglect of line-of-sight coupling of two foreground lenses in the standard first order result. These terms alter the convergence ($\kappa\kappa$), the lensing shear E-mode ($\epsilon\epsilon$), and their cross-correlation ($\kappa\epsilon$) power spectra on large angular scales, but leave the power spectra of the lensing shear B-mode ($\beta\beta$) and rotational ($\omega\omega$) component unchanged as compared to previous estimates. The new terms complete the calculation of corrections to weak lensing angular power spectra associated with both the Born approximation and the lens-lens coupling to an order in which the contributions are most significant. Taking these features together, we find that these corrections are unimportant for any weak lensing survey, including for a full sky survey limited by cosmic variance.Comment: Added references, minor changes to text. 9 pages, 2 figure

Cosmology with variable parameters and effective equation of state for Dark Energy

A cosmological constant, Lambda, is the most natural candidate to explain the origin of the dark energy (DE) component in the Universe. However, due to experimental evidence that the equation of state (EOS) of the DE could be evolving with time/redshift (including the possibility that it might behave phantom-like near our time) has led theorists to emphasize that there might be a dynamical field (or some suitable combination of them) that could explain the behavior of the DE. While this is of course one possibility, here we show that there is no imperative need to invoke such dynamical fields and that a variable cosmological constant (including perhaps a variable Newton's constant too) may account in a natural way for all these features.Comment: LaTeX, 9 pages, 1 figure. Talk given at the 7th Intern. Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT 05

On general features of warm dark matter with reduced relativistic gas

Reduced Relativistic Gas (RRG) is a useful approach to describe the warm dark matter (WDM) or the warmness of baryonic matter in the approximation when the interaction between the particles is irrelevant. The use of Maxwell distribution leads to the complicated equation of state of the J\"{u}ttner model of relativistic ideal gas. The RRG enables one to reproduce the same physical situation but in a much simpler form. For this reason RRG can be a useful tool for the theories with some sort of a "new Physics". On the other hand, even without the qualitatively new physical implementations, the RRG can be useful to describe the general features of WDM in a model-independent way. In this sense one can see, in particular, to which extent the cosmological manifestations of WDM may be dependent on its Particle Physics background. In the present work RRG is used as a complementary approach to derive the main observational exponents for the WDM in a model-independent way. The only assumption concerns a non-negligible velocity $v$ for dark matter particles which is parameterized by the warmness parameter $b$. The relatively high values of $b$ ( $b^2\gtrsim 10^{-6}$) erase the radiation (photons and neutrinos) dominated epoch and cause an early warm matter domination after inflation. Furthermore, RRG approach enables one to quantify the lack of power in linear matter spectrum at small scales and in particular, reproduces the relative transfer function commonly used in context of WDM with accuracy of $\lesssim 1\%$. A warmness with $b^2\lesssim 10^{-6}$ (equivalent to $v\lesssim 300 km/s$) does not alter significantly the CMB power spectrum and is in agreement with the background observational tests.Comment: 15 pages, 8 figures. Essential improvements in style and presentatio