1,744 research outputs found
Metastable SUSY Breaking and Supergravity at Finite Temperature
We study how coupling to supergravity affects the phase structure of a system
exhibiting dynamical supersymmetry breaking in a metastable vacuum. More
precisely, we consider the Seiberg dual of SQCD coupled to supergravity at
finite temperature. We show that the gravitational interactions decrease the
critical temperature for the second order phase transition in the quark
direction, that is also present in the global case. Furthermore, we find that,
due to supergravity, a new second order phase transition occurs in the meson
direction, whenever there is a nonvanishing constant term in the
superpotential. Notably, this phase transition is a necessary condition for the
fields to roll, as the system cools down, towards the metastable susy breaking
vacuum, because of the supergravity-induced shift of the metastable minimum
away from zero meson vevs. Finally, we comment on the phase structure of the
KKLT model with uplifting sector given by the Seiberg dual of SQCD.Comment: 38 pages; Section 6 amended and expanded, references adde
Roundabout relaxation: collective excitation requires a detour to equilibrium
Relaxation to equilibrium after strong and collective excitation is studied,
by using a Hamiltonian dynamical system of one dimensional XY model. After an
excitation of a domain of elements, the excitation is concentrated to fewer
elements, which are made farther away from equilibrium, and the excitation
intensity increases logarithmically with . Equilibrium is reached only after
taking this ``roundabout'' route, with the time for relaxation diverging
asymptotically as with .Comment: 4 pages, 5 figure
Exact Casimir-Polder potentials: interaction of an atom with a conductor-patched dielectric surface
We study the interaction between a neutral atom or molecule and a
conductor-patched dielectric surface. We model this system by a perfectly
reflecting disc lying atop of a non-dispersive dielectric half-space, both
interacting with the neutral atom or molecule. We assume the interaction to be
non-retarded and at zero temperature. We find an exact solution to this
problem. In addition we generate a number of other useful results. For the case
of no substrate we obtain the exact formula for the van der Waals interaction
energy of an atom near a perfectly conducting disc. We show that the
Casimir-Polder force acting on an atom that is polarized in the direction
normal to the surface of the disc displays intricate behaviour. This part of
our results is directly relevant to recent matter-wave experiments in which
cold molecules are scattered by a radially symmetric object in order to study
diffraction patterns and the so-called Poisson spot. Furthermore, we give an
exact expression for the non-retarded limit of the Casimir-Polder interaction
between an atom and a perfectly-conducting bowl.Comment: 9 pages, 9 figure
Self-Organized Bottleneck in Energy Relaxation
We study an energy relaxation process after many degrees of freedom are
excited in a Hamiltonian system with a large number of degrees of freedom.
Bottlenecks of relaxation, where relaxations of the excited elements are
drastically slowed down, are discovered. By defining an internal state for the
excited degrees of freedom, it is shown that the drastic slowing down occurs
when the internal state is in a critical state. The relaxation dynamics brings
the internal state into the critical state, and the critical bottleneck of
relaxation is self-organized. Relevance of our result to relaxation phenomena
in condensed matters or large molecules is briefly discussed.Comment: 4pages, 5 figure
A Near-Infrared Spectroscopic Study of the Accreting Magnetic White Dwarf SDSS J121209.31+013627.7 and its Substellar Companion
The nature of the excess near-infrared emission associated with the magnetic
white dwarf commonly known as SDSS 1212 is investigated primarily through
spectroscopy, and also via photometry. The inferred low mass secondary in this
system has been previously detected by the emission and variation of H,
and the m spectral data presented here are consistent with the
presence of a late L or early T dwarf. The excess flux seen beyond 1.5 m
in the phase-averaged spectrum is adequately modeled with an L8 dwarf
substellar companion and cyclotron emission in a 7 MG magnetic field. This
interesting system manifests several observational properties typical of
polars, and is most likely an old interacting binary with a magnetic white
dwarf and a substellar donor in an extended low state.Comment: 28 pages, 5 figures, Accepted to Ap
On the Gravitational Collapse of a Gas Cloud in Presence of Bulk Viscosity
We analyze the effects induced by the bulk viscosity on the dynamics
associated to the extreme gravitational collapse. Aim of the work is to
investigate whether the presence of viscous corrections to the evolution of a
collapsing gas cloud influence the fragmentation process. To this end we study
the dynamics of a uniform and spherically symmetric cloud with corrections due
to the negative pressure contribution associated to the bulk viscosity
phenomenology. Within the framework of a Newtonian approach (whose range of
validity is outlined), we extend to the viscous case either the Lagrangian,
either the Eulerian motion of the system and we treat the asymptotic evolution
in correspondence to a viscosity coefficient of the form ( being the cloud density and ). We show how,
in the adiabatic-like behavior of the gas (i.e. when the politropic index takes
values ), density contrasts acquire, asymptotically, a
vanishing behavior which prevents the formation of sub-structures. We can
conclude that in the adiabatic-like collapse the top down mechanism of
structures formation is suppressed as soon as enough strong viscous effects are
taken into account. Such a feature is not present in the isothermal-like (i.e.
) collapse because the sub-structures formation is yet present
and outlines the same behavior as in the non-viscous case. We emphasize that in
the adiabatic-like collapse the bulk viscosity is also responsible for the
appearance of a threshold scale beyond which perturbations begin to increase.Comment: 13 pages, no figur
Direct Dark Matter Detection with Velocity Distribution in the Eddington approach
Exotic dark matter together with the vacuum energy (associated with the
cosmological constant) seem to dominate the Universe. Thus its direct detection
is central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). One
essential ingredient in obtaining the direct detection rates is the density and
the velocity distribution of the LSP in our vicinity. In the present paper we
study simultaneously density profiles and velocity distributions in the context
of the Eddington approach. In such an approach, unlike the commonly assumed
Maxwell-Boltzmann (M-B) distribution, the upper bound of the velocity arises
naturally from the potential.Comment: 21 LaTex pages, 27 figure
Self-consistent models of cuspy triaxial galaxies with dark matter haloes
We have constructed realistic, self-consistent models of triaxial elliptical
galaxies embedded in triaxial dark matter haloes. We examined three different
models for the shape of the dark matter halo: (i) the same axis ratios as the
luminous matter (0.7:0.86:1); (ii) a more prolate shape (0.5:0.66:1); (iii) a
more oblate shape (0.7:0.93:1). The models were obtained by means of the
standard orbital superposition technique introduced by Schwarzschild.
Self-consistent solutions were found in each of the three cases. Chaotic orbits
were found to be important in all of the models,and their presence was shown to
imply a possible slow evolution of the shapes of the haloes. Our results
demonstrate for the first time that triaxial dark matter haloes can co-exist
with triaxial galaxies.Comment: Latex paper based on the AASTEX format, 20 pages, 11 figures, 2
tables. Paper submitted to Ap
Estimate of blow-up and relaxation time for self-gravitating Brownian particles and bacterial populations
We determine an asymptotic expression of the blow-up time t_coll for
self-gravitating Brownian particles or bacterial populations (chemotaxis) close
to the critical point. We show that t_coll=t_{*}(eta-eta_c)^{-1/2} with
t_{*}=0.91767702..., where eta represents the inverse temperature (for Brownian
particles) or the mass (for bacterial colonies), and eta_c is the critical
value of eta above which the system blows up. This result is in perfect
agreement with the numerical solution of the Smoluchowski-Poisson system. We
also determine the asymptotic expression of the relaxation time close but above
the critical temperature and derive a large time asymptotic expansion for the
density profile exactly at the critical point
The evolution and energetics of large amplitude nonlinear internal waves on the Portuguese shelf
Intensive in-situ observations of nonlinear internal waves on the Portuguese shelf were made in August 1994, including measurements of the same wavepacket at three locations as it propagated on-shelf. The waves were characterized by sudden isotherm depressions of up to 45 m lasting 10-35 minutes, accompanied by current surges of up to 0.45 m s-1 and shears of up to 0.7 m s-1 over 60 m. The waves propagated away from the shelf break with an estimated phase speed of 0.57 m s-1. The amplitude of the waves was comparable to the theoretical maximum. The kinetic and potential energies of the waves were calculated directly from the observed current and density structures. Individual waves were associated with a total energy of up to approximately 3.0 M J m-1 per unit crest length. The depth integrated on-shelf internal wave energy flux approached 2000 W m-1 per unit crest length near the shelf break and decreased on-shore at a depth integrated rate of approximately 7.7 Ă 10-2 W m-2. The internal waves provided an important source of vertical mixing where they occurred on the Portuguese shelf throughout most of August 1994, represented by a sustained vertical eddy diffusivity profile which peaked at Kz â 2.2 Ă 10-3 m2 s-1 at 30 m depth. Internal mixing would have to be parameterized by such a Kz profile in any model of the Portuguese shelf in which the stratification were to be accurately represented
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