A new window on Strange Quark Matter as the ground state of strongly interacting matter

If strange quark matter is the true ground state of matter, it must have lower energy than nuclear matter. Simultaneously, two-flavour quark matter must have higher energy than nuclear matter, for otherwise the latter would convert to the former. We show, using an effective chiral lagrangian, that the existence of a new lower energy ground state for two-flavour quark matter, the pion condensate, shrinks the window for strange quark matter to be the ground state of matter and sets new limits on the current strange quark mass

Collisional Velocities and Rates in Resonant Planetesimal Belts

We consider a belt of small bodies around a star, captured in one of the external or 1:1 mean-motion resonances with a massive perturber. The objects in the belt collide with each other. Combining methods of celestial mechanics and statistical physics, we calculate mean collisional velocities and collisional rates, averaged over the belt. The results are compared to collisional velocities and rates in a similar, but non-resonant belt, as predicted by the particle-in-a-box method. It is found that the effect of the resonant lock on the velocities is rather small, while on the rates more substantial. The collisional rates between objects in an external resonance are by about a factor of two higher than those in a similar belt of objects not locked in a resonance. For Trojans under the same conditions, the collisional rates may be enhanced by up to an order of magnitude. Our results imply, in particular, shorter collisional lifetimes of resonant Kuiper belt objects in the solar system and higher efficiency of dust production by resonant planetesimals in debris disks around other stars.Comment: 31 pages, 11 figures (some of them heavily compressed to fit into arxiv-maximum filesize), accepted for publication at "Celestial Mechanics and Dynamical Astronomy

SU(N) Antiferromagnets and Strongly Coupled QED: Effective Field Theory for Josephson Junctions Arrays

We review our analysis of the strong coupling of compact QED on a lattice with staggered Fermions. We show that, for infinite coupling, compact QED is exactly mapped in a quantum antiferromagnet. We discuss some aspects of this correspondence relevant for effective field theories of Josephson junctions arrays.Comment: 33 pages,latex,Proceedings of "Common Trends in Condensed Matter and High Energy Physics",DFUPG 1/9

SU(N) Quantum Antiferromagnets and the Phase Structure of QED in the Strong Coupling Limit

We examine the strong coupling limit of both compact and non compact QED on a lattice with staggered fermions. We show that every SU(N) antiferromagnet with spins in a particular fundamental representation of the SU(N) Lie Algebra and with nearest neighbor couplings on a bipartite lattice is exactly equivalent to the infinite coupling limit of lattice QED with the numbers of flavors of electrons related to N and the dimension of spacetime D+1. We find that,for both compact and noncompact QED,when N is odd the ground state of the strong coupling limit breaks chiral symmetry in any dimensions and for any N and the condensate is an isoscalar mass operator. When N is even,chiral symmetry is broken if D is bigger or equal to 2 and N is small enough and the order parameter is an isovector mass operator. We also find the exact ground state of the lattice Coulomb gas as well as a variety of related lattice statistical systems with long ranged interactions.Comment: latex, 45 pages, DFUPG 69/9

Low-lying meson spectrum of large NCN_C strongly coupled lattice QCD

We compute the low energy mass spectrum of lattice QCD in the large $N_C$ limit. Expanding around a gauge-invariant ground state, which spontaneously breaks the discrete chiral symmetry, we derive an improved strong-coupling expansion and evaluate, for any value of $N_C$, the masses of the low-lying states in the unflavored meson spectrum. We then take the 't Hooft limit by rescaling $g^2 N_C\to g^2$; the 't Hooft limit is smooth and no arbitrary parameters are needed. We find, already at the fourth order of the strong coupling perturbation theory, a very good agreement between the results of our lattice computation and the known continuum values.Comment: 43 pages, 1 figure. Minor corrections. One reference added in section

Meson screening masses from lattice QCD with two light and the strange quark

We present results for screening masses of mesons built from light and strange quarks in the temperature range of approximately between 140 MeV to 800 MeV. The lattice computations were performed with 2+1 dynamical light and strange flavors of improved (p4) staggered fermions along a line of constant physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The lattices had temporal extents Nt = 4, 6 and 8 and aspect ratios of Ns / Nt \geq 4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass remains almost equal to the corresponding zero temperature pseudo-scalar (pole) mass. At temperatures around 3Tc (Tc being the transition temperature) the continuum extrapolated pseudo-scalar screening mass approaches very close to the free continuum result of 2 \pi T from below. On the other hand, at high temperatures the vector screening mass turns out to be larger than the free continuum value of 2 \pi T. The pseudo-scalar and the vector screening masses do not become degenerate even for a temperature as high as 4Tc. Using these mesonic spatial correlation functions we have also investigated the restoration of chiral symmetry and the effective restoration of the axial symmetry. We have found that the vector and the axial-vector screening correlators become degenerate, indicating chiral symmetry restoration, at a temperature which is consistent with the QCD transition temperature obtained in previous studies. On the other hand, the pseudo-scalar and the scalar screening correlators become degenerate only at temperatures larger than 1.3Tc, indicating that the effective restoration of the axial symmetry takes place at a temperature larger than the QCD transition temperature.Comment: Published versio

The Kuiper Belt and Other Debris Disks

We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book "Astrophysics in the Next Decade

The accelerated scaling attractor solution of the interacting agegraphic dark energy in Brans-Dicke theory

We investigate the interacting agegraphic dark energy in Brans-Dicke theory and introduce a new series general forms of dark sector coupling. As examples, we select three cases involving a linear interaction form (Model I) and two nonlinear interaction form (Model II and Model III). Our conclusions show that the accelerated scaling attractor solutions do exist in these models. We also find that these interacting agegraphic dark energy modes are consistent with the observational data. The difference in these models is that nonlinear interaction forms give more approached evolution to the standard $\Lambda$CDM model than the linear one. Our work implies that the nonlinear interaction forms should be payed more attention.Comment: 9 pages, 10 figures, accepted in Eur. Phys. J.

Contraints on unified models for dark matter and dark energy using H(z)

The differential age data of astrophysical objects that have evolved passivelly during the history of the universe (e.g. red galaxies) allows to test theoretical cosmological models through the predicted Hubble function expressed in terms of the redshift $z$, $H(z)$. We use the observational data for $H(z)$ to test unified scenarios for dark matter and dark energy. Specifically, we focus our analysis on the Generalized Chaplygin Gas (GCG) and the viscous fluid (VF) models. For the GCG model, it is shown that the unified scenario for dark energy and dark matter requires some priors. For the VF model we obtain estimations for the free parameters that may be compared with further analysis mainly at perturbative level.Comment: Latex file, 10 pages, 19 figures in eps format. Accepted for publication in European Journal of Physics