879 research outputs found
Self-consistency and collective effects in semiclassical pairing theory
A simple model, in which nuclei are represented as homogeneous spheres of
symmetric nuclear matter, is used to study the effects of a self-consistent
pairing interaction on the nuclear response. Effects due to the finite size of
nuclei are suitably taken into account. The semiclassical equations of motion
derived in a previous paper for the time-dependent Hartree-Fock-Bogoliubov
problem are solved in an improved (linear) approximation in which the pairing
field is allowed to oscillate and to become complex. The new solutions are in
good agreement with the old ones and also with the result of well-known quantum
approaches. The role of the Pauli principle in eliminating one possible set of
solutions is also discussed. The pairing-field fluctuations have two main
effects: they restore the particle-number symmetry which is broken in the
constant- approximation and introduce the possibility of collective
eigenfrequencies of the system due to the pairing interaction. A numerical
study with values of parameters appropriate for nuclei, shows an enhancement of
the density-density strength function in the region of the low-energy giant
octupole resonance, while no similar effect is present in the region of the
high-energy octupole resonance and for the giant monopole and quadrupole
resonances.Comment: 31 pages, 6 eps figure
Viral Retinitis following Intraocular or Periocular Corticosteroid Administration: A Case Series and Comprehensive Review of the Literature.
Abstract Purpose: To describe viral retinitis following intravitreal and periocular corticosteroid administration. Methods: Retrospective case series and comprehensive literature review. Results: We analyzed 5 unreported and 25 previously published cases of viral retinitis following local corticosteroid administration. Causes of retinitis included 23 CMV (76.7%), 5 HSV (16.7%), and 1 each VZV and unspecified (3.3%). Two of 22 tested patients (9.1%) were HIV positive. Twenty-one of 30 (70.0%) cases followed one or more intravitreal injections of triamcinolone acetonide (TA), 4 (13.3%) after one or more posterior sub-Tenon injections of TA, 3 (10.0%) after placement of a 0.59-mg fluocinolone acetonide implant (Retisert), and 1 (3.3%) each after an anterior subconjunctival injection of TA (together with IVTA), an anterior chamber injection, and an anterior sub-Tenon injection. Mean time from most recent corticosteroid administration to development of retinitis was 4.2 months (median 3.8; range 0.25-13.0). Twelve patients (40.0%) had type II diabetes mellitus. Treatments used included systemic antiviral agents (26/30, 86.7%), intravitreal antiviral injections (20/30, 66.7%), and ganciclovir intravitreal implants (4/30, 13.3%). Conclusions: Viral retinitis may develop or reactivate following intraocular or periocular corticosteroid administration. Average time to development of retinitis was 4 months, and CMV was the most frequently observed agent. Diabetes was a frequent co-morbidity and several patients with uveitis who developed retinitis were also receiving systemic immunosuppressive therapy
Bohmian mechanics, the quantum-classical correspondence and the classical limit: the case of the square billiard
Square billiards are quantum systems complying with the dynamical
quantum-classical correspondence. Hence an initially localized wavefunction
launched along a classical periodic orbit evolves along that orbit, the
spreading of the quantum amplitude being controlled by the spread of the
corresponding classical statistical distribution. We investigate wavepacket
dynamics and compute the corresponding de Broglie-Bohm trajectories in the
quantum square billiard. We also determine the trajectories and statistical
distribution dynamics for the equivalent classical billiard. Individual Bohmian
trajectories follow the streamlines of the probability flow and are generically
non-classical. This can also hold even for short times, when the wavepacket is
still localized along a classical trajectory. This generic feature of Bohmian
trajectories is expected to hold in the classical limit. We further argue that
in this context decoherence cannot constitute a viable solution in order to
recover classicality.Comment: Figures downgraded to low resolution; To be published in Found. Phys.
(2009)
EPR-Bell Nonlocality, Lorentz Invariance, and Bohmian Quantum Theory
We discuss the problem of finding a Lorentz invariant extension of Bohmian
mechanics. Due to the nonlocality of the theory there is (for systems of more
than one particle) no obvious way to achieve such an extension. We present a
model invariant under a certain limit of Lorentz transformations, a limit
retaining the characteristic feature of relativity, the non-existence of
absolute time resp. simultaneity. The analysis of this model exemplifies an
important property of any Bohmian quantum theory: the quantum equilibrium
distribution cannot simultaneously be realized in all
Lorentz frames of reference.Comment: 24 pages, LaTex, 4 figure
Ground State and Quasiparticle Spectrum of a Two Component Bose-Einstein Condensate
We consider a dilute atomic Bose-Einstein condensate with two non-degenerate
internal energy levels. The presence of an external radiation field can result
in new ground states for the condensate which result from the lowering of the
condensate energy due to the interaction energy with the field. In this
approach there are no instabilities in the quasiparticle spectrum as was
previously found by Goldstein and Meystre (Phys. Rev. A \QTR{bf}{55}, 2935
(1997)).Comment: 20 pages, 2 figures RevTex. Submitted to Phys. Rev. A; Revised
versio
Instabilities in a Two-Component, Species Conserving Condensate
We consider a system of two species of bosons of equal mass, with
interactions and for bosons of the same and different
species respectively. We present a rigorous proof -- valid when the Hamiltonian
does not include a species switching term -- showing that, when
, the ground state is fully "polarized" (consists of
atoms of one kind only). In the unpolarized phase the low energy excitation
spectrum corresponds to two linearly dispersing modes that are even a nd odd
under species exchange. The polarization instability is signaled by the vani
shing of the velocity of the odd modes.Comment: To appear in Phys. Rev.
Moduli and (un)attractor black hole thermodynamics
We investigate four-dimensional spherically symmetric black hole solutions in
gravity theories with massless, neutral scalars non-minimally coupled to gauge
fields. In the non-extremal case, we explicitly show that, under the variation
of the moduli, the scalar charges appear in the first law of black hole
thermodynamics. In the extremal limit, the near horizon geometry is
and the entropy does not depend on the values of moduli at
infinity. We discuss the attractor behaviour by using Sen's entropy function
formalism as well as the effective potential approach and their relation with
the results previously obtained through special geometry method. We also argue
that the attractor mechanism is at the basis of the matching between the
microscopic and macroscopic entropies for the extremal non-BPS Kaluza-Klein
black hole.Comment: 36 pages, no figures, V2: minor changes, misprints corrected,
expanded references; V3: sections 4.3 and 4.5 added; V4: minor changes,
matches the published versio
On the single mode approximation in spinor-1 atomic condensate
We investigate the validity conditions of the single mode approximation (SMA)
in spinor-1 atomic condensate when effects due to residual magnetic fields are
negligible. For atomic interactions of the ferromagnetic type, the SMA is shown
to be exact, with a mode function different from what is commonly used.
However, the quantitative deviation is small under current experimental
conditions (for Rb atoms). For anti-ferromagnetic interactions, we find
that the SMA becomes invalid in general. The differences among the mean field
mode functions for the three spin components are shown to depend strongly on
the system magnetization. Our results can be important for studies of beyond
mean field quantum correlations, such as fragmentation, spin squeezing, and
multi-partite entanglement.Comment: Revised, newly found analytic proof adde
alpha'-exact entropies for BPS and non-BPS extremal dyonic black holes in heterotic string theory from ten-dimensional supersymmetry
We calculate near-horizon solutions for four-dimensional 4-charge and
five-dimensional 3-charge black holes in heterotic string theory from the part
of the ten-dimensional tree-level effective action which is connected to
gravitational Chern-Simons term by supersymmetry. We obtain that the entropies
of large black holes exactly match the alpha'-exact statistical entropies
obtained from microstate counting (D=4) and AdS/CFT correspondence (D=5).
Especially interesting is that we obtain agreement for both BPS and non-BPS
black holes, contrary to the case of R^2-truncated (four-derivative) actions
(D-dimensional N=2 off-shell supersymmetric or Gauss-Bonnet) were used, which
give the entropies agreeing (at best) just for BPS black holes. The key
property of the solutions, which enabled us to tackle the action containing
infinite number of terms, is vanishing of the Riemann tensor \bar{R}_{MNPQ}
obtained from torsional connection defined with \bar{\Gamma} = \Gamma - H/2.
Morover, if every monomial of the remaining part of the effective action would
contain at least two Riemanns \bar{R}_{MNPQ}, it would trivially follow that
our solutions are exact solutions of the full heterotic effective action in
D=10. The above conjecture, which appeared (in this or stronger form) from time
to time in the literature, has controversial status, but is supported by the
most recent calculations of Richards (arXiv:0807.3453 [hep-th]). Agreement of
our results for the entropies with the microscopic ones supports the
conjecture. As for small black holes, our solutions in D=5 still have singular
horizons.Comment: 28 pages; v2: minor changes, references added; v3: extended
discussion on small black holes in sec. 5.4, more references added, accepted
in JHE
The dynamics of quantum phases in a spinor condensate
We discuss the quantum phases and their diffusion dynamics in a spinor-1
atomic Bose-Einstein condensate. For ferromagnetic interactions, we obtain the
exact ground state distribution of the phases associated with the total atom
number (), the total magnetization (), and the alignment (or
hypercharge) () of the system. The mean field ground state is stable against
fluctuations of atom numbers in each of the spin components, and the phases
associated with the order parameter for each spin components diffuse while
dynamically recover the two broken continuous symmetries [U(1) and SO(2)] when
and are conserved as in current experiments. We discuss the
implications to the quantum dynamics due to an external (homogeneous) magnetic
field. We also comment on the case of a spinor-1 condensate with
anti-ferromagnetic interactions.Comment: 5 figures, an extended version of cond-mat/030117
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