96 research outputs found
Abundant stable gauge field hair for black holes in anti-de sitter space
We present new hairy black hole solutions of SU(N) Einstein-Yang-Mills (EYM) theory in asymptotically anti–de Sitter (AdS) space. These black holes are described by N+1 independent parameters and have N-1 independent gauge field degrees of freedom. Solutions in which all gauge field functions have no zeros exist for all N, and for a sufficiently large (and negative) cosmological constant. At least some of these solutions are shown to be stable under classical, linear, spherically symmetric perturbations. Therefore there is no upper bound on the amount of stable gauge field hair with which a black hole in AdS can be endowed
The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry
The phase diagram of model anisotropic particles with four attractive patches
in a tetrahedral arrangement has been computed at two different values for the
range of the potential, with the aim of investigating the conditions under
which a diamond crystal can be formed. We find that the diamond phase is never
stable for our longer-ranged potential. At low temperatures and pressures, the
fluid freezes into a body-centred-cubic solid that can be viewed as two
interpenetrating diamond lattices with a weak interaction between the two
sublattices. Upon compression, an orientationally ordered face-centred-cubic
crystal becomes more stable than the body-centred-cubic crystal, and at higher
temperatures a plastic face-centered-cubic phase is stabilized by the increased
entropy due to orientational disorder. A similar phase diagram is found for the
shorter-ranged potential, but at low temperatures and pressures, we also find a
region over which the diamond phase is thermodynamically favored over the
body-centred-cubic phase. The higher vibrational entropy of the diamond
structure with respect to the body-centred-cubic solid explains why it is
stable even though the enthalpy of the latter phase is lower. Some preliminary
studies on the growth of the diamond structure starting from a crystal seed
were performed. Even though the diamond phase is never thermodynamically stable
for the longer-ranged model, direct coexistence simulations of the interface
between the fluid and the body-centred-cubic crystal and between the fluid and
the diamond crystal show that, at sufficiently low pressures, it is quite
probable that in both cases the solid grows into a diamond crystal, albeit
involving some defects. These results highlight the importance of kinetic
effects in the formation of diamond crystals in systems of patchy particles.Comment: 15 pages, 13 figure
Quantum State Reconstruction of a Bose-Einstein Condensate
We propose a tomographic scheme to reconstruct the quantum state of a
Bose-Einstein condensate, exploiting the radiation field as a probe and
considering the atomic internal degrees of freedom. The density matrix in the
number state basis can be directly retrieved from the atom counting
probabilities.Comment: 11 pages, LaTeX file, no figures, to appear in Europhysics Letter
Bell-state preparation for electron spins in a semiconductor double quantum dot
A robust scheme for state preparation and state trapping for the spins of two
electrons in a semiconductor double quantum dot is presented. The system is
modeled by two spins coupled to two independent bosonic reservoirs. Decoherence
effects due to this environment are minimized by application of optimized
control fields which make the target state to the ground state of the isolated
driven spin system. We show that stable spin entanglement with respect to pure
dephasing is possible. Specifically, we demonstrate state trapping in a
maximally entangled state (Bell state) in the presence of decoherence.Comment: 9 pages, 4 figure
Soliton and black hole solutions of su(N) Einstein-Yang-Mills theory in anti-de Sitter space
We present new soliton and hairy black hole solutions of su(N)
Einstein-Yang-Mills theory in asymptotically anti-de Sitter space. These
solutions are described by N+1 independent parameters, and have N-1 gauge field
degrees of freedom. We examine the space of solutions in detail for su(3) and
su(4) solitons and black holes. If the magnitude of the cosmological constant
is sufficiently large, we find solutions where all the gauge field functions
have no zeros. These solutions are of particular interest because we anticipate
that at least some of them will be linearly stable.Comment: 15 pages, 20 figures, minor changes, accepted for publication in
Physical Review
Properties of canonical determinants and a test of fugacity expansion for finite density lattice QCD with Wilson fermions
We analyze canonical determinants, i.e., grand canonical determinants
projected to a fixed net quark number. The canonical determinants are the
coefficients in a fugacity expansion of the grand canonical determinant and we
evaluate them as the Fourier moments of the grand canonical determinant with
respect to imaginary chemical potential, using a dimensional reduction
technique. The analysis is done for two mass-degenerate flavors of Wilson
fermions at several temperatures below and above the confinement/deconfinement
crossover. We discuss various properties of the canonical determinants and
analyse the convergence of the fugacity series for different temperatures.Comment: Typo removed, paragraph added in the discussion. Version to appear in
Phys. Rev.
Adiabatic Formation of Rydberg Crystals with Chirped Laser Pulses
Ultracold atomic gases have been used extensively in recent years to realize
textbook examples of condensed matter phenomena. Recently, phase transitions to
ordered structures have been predicted for gases of highly excited, 'frozen'
Rydberg atoms. Such Rydberg crystals are a model for dilute metallic solids
with tunable lattice parameters, and provide access to a wide variety of
fundamental phenomena. We investigate theoretically how such structures can be
created in four distinct cold atomic systems, by using tailored
laser-excitation in the presence of strong Rydberg-Rydberg interactions. We
study in detail the experimental requirements and limitations for these
systems, and characterize the basic properties of small crystalline Rydberg
structures in one, two and three dimensions.Comment: 23 pages, 10 figures, MPIPKS-ITAMP Tandem Workshop, Cold Rydberg
Gases and Ultracold Plasmas (CRYP10), Sept. 6-17, 201
Vacuum polarization for lukewarm black holes
We compute the renormalized expectation value of the square of a quantum scalar field on a Reissner-Nordström–de Sitter black hole in which the temperatures of the event and cosmological horizons are equal (“lukewarm” black hole). Our numerical calculations for a thermal state at the same temperature as the two horizons indicate that this renormalized expectation value is regular on both the event and cosmological horizons. We are able to show analytically, using an approximation for the field modes near the horizons, that this is indeed the case
Director configuration of planar solitons in nematic liquid crystals
The director configuration of disclination lines in nematic liquid crystals
in the presence of an external magnetic field is evaluated. Our method is a
combination of a polynomial expansion for the director and of further
analytical approximations which are tested against a numerical shooting method.
The results are particularly simple when the elastic constants are equal, but
we discuss the general case of elastic anisotropy. The director field is
continuous everywhere apart from a straight line segment whose length depends
on the value of the magnetic field. This indicates the possibility of an
elongated defect core for disclination lines in nematics due to an external
magnetic field.Comment: 12 pages, Revtex, 8 postscript figure
Dyons and dyonic black holes in Einstein-Yang-Mills theory in anti-de Sitter space-time
We present new spherically symmetric, dyonic soliton and black hole solutions of the Einstein-Yang-Mills equations in four-dimensional asymptotically anti-de Sitter space-time. The gauge field has nontrivial electric and magnetic components and is described by magnetic gauge field functions and electric gauge field functions. We explore the phase space of solutions in detail for and gauge groups. Combinations of the electric gauge field functions are monotonic and have no zeros; in general the magnetic gauge field functions may have zeros. The phase space of solutions is extremely rich, and we find solutions in which the magnetic gauge field functions have more than fifty zeros. Of particular interest are solutions for which the magnetic gauge field functions have no zeros, which exist when the negative cosmological constant has sufficiently large magnitude. We conjecture that at least some of these nodeless solutions may be stable under linear, spherically symmetric, perturbations
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