437 research outputs found
Non-BPS Dyons and Branes in the Dirac-Born-Infeld Theory
Non-BPS dyon solutions to D3-brane actions are constructed when one or more
scalar fields describing transverse fluctuations of the brane, are considered.
The picture emerging from such non-BPS configurations is analysed, in
particular the response of the D-brane-string system to small perturbations.Comment: 16 pages, 4 figures, Revtex fil
Quantum noise in current biased Josephson junction
Quantum fluctuations in a current biased Josephson junction, described in
terms of the RCSJ-model, are considered. The fluctuations of the voltage and
phase across the junction are assumed to be initiated by equilibrium current
fluctuations in the shunting resistor. This corresponds to low enough
temperatures, when fluctuations of the normal current in the junction itself
can be neglected. We used the quantum Langevin equation in terms of random
variables related to the limit cycle of the nonlinear Josephson oscillator.
This allows to go beyond the perturbation theory and calculate the widths of
the Josephson radiation lines
Exact Path-Integral Representations for the -Matrix in Nonrelativistic Potential Scattering
Several path integral representations for the -matrix in nonrelativistic
potential scattering are given which produce the complete Born series when
expanded to all orders and the eikonal approximation if the quantum
fluctuations are suppressed. They are obtained with the help of "phantom"
degrees of freedom which take away explicit phases that diverge for asymptotic
times. Energy conservation is enforced by imposing a Faddeev-Popov-like
constraint in the velocity path integral. An attempt is made to evaluate
stochastically the real-time path integral for potential scattering and
generalizations to relativistic scattering are discussed.Comment: 6 pages, 2 figures. Contribution to the workshop "Relativistic
Description of Two- and Three-Body Systems in Nuclear Physics", ETC*, October
19-23, 2009. v2: typo corrected, matches published version + additional
reference
Unusual bound states of quark matter within the NJL model
Properties of dense quark matter in and out of chemical equilibrium are
studied within the SU(3) Nambu-Jona-Lasinio model. In addition to the 4-fermion
scalar and vector terms the model includes also the 6-fermion flavour mixing
interaction. First we study a novel form of deconfined matter, meso-matter,
which is composed of equal number of quarks and antiquarks. It can be thought
of as a strongly compressed meson gas where mesons are melted into their
elementary constituents, quarks and antiquarks. Strongly bound states in this
quark-antiquark matter are predicted for all flavour combinations of
quark-antiquark pairs. The maximum binding energy reaches up to 180 MeV per
pair for mixtures with about 70% of strange quark-antiquark pairs. Equilibrated
baryon-rich quark matter with various flavour compositions is also studied. In
this case only shallow bound states appear in systems with a significant
admixture (about 40%) of strange quarks (strangelets). Their binding energies
are quite sensitive to the relative strengths of scalar and vector
interactions. The common property of all these bound states is that they appear
at high particle densities when the chiral symmetry is nearly restored. Thermal
properties of meso-matter as well as chemically equilibrated strange quark
matter are also investigated. Possible decay modes of these bound states are
discussed.Comment: 26 pages, 16 PostScript figures, RevTe
Mesons in gauge/gravity dual with large number of fundamental fields
In view of extending gauge/gravity dualities with flavour beyond the probe
approximation, we establish the gravity dual description of mesons for a
three-dimensional super Yang-Mills theory with fundamental matter. For this
purpose we consider the fully backreacted D2/D6 brane solution of Cherkis and
Hashimoto in an approximation due to Pelc and Siebelink. The low-energy field
theory is the IR fixed point theory of three-dimensional N=4 SU(N_c) super
Yang-Mills with N_f fundamental fields, which we consider in a large N_c and
N_f limit with N_f/N_c finite and fixed. We discuss the dictionary between
meson-like operators and supergravity fluctuations in the corresponding
near-horizon geometry. In particular, we find that the mesons are dual to the
low-energy limit of closed string states. In analogy to computations of
glueball mass spectra, we calculate the mass of the lowest-lying meson and find
that it depends linearly on the quark mass.Comment: 19 pages, LaTeX, 6 figures, v2: fig. 4 added, refs. adde
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
âIn these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.â Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T †5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Integer quantum Hall effect for hard-core bosons and a failure of bosonic Chern-Simons mean-field theories for electrons at half-filled Landau level
Field-theoretical methods have been shown to be useful in constructing simple
effective theories for two-dimensional (2D) systems. These effective theories
are usually studied by perturbing around a mean-field approximation, so the
question whether such an approximation is meaningful arises immediately. We
here study 2D interacting electrons in a half-filled Landau level mapped onto
interacting hard-core bosons in a magnetic field. We argue that an interacting
hard-core boson system in a uniform external field such that there is one flux
quantum per particle (unit filling) exhibits an integer quantum Hall effect. As
a consequence, the mean-field approximation for mapping electrons at
half-filling to a boson system at integer filling fails.Comment: 13 pages latex with revtex. To be published in Phys. Rev.
Curvature Dependence of Running Gauge Coupling and Confinement in AdS/CFT Correspondence
We construct IIB supergravity (viewed as dilatonic gravity) background with
non-trivial dilaton and with curved four-dimensional space. Such a background
may describe another vacuum of maximally supersymmetric Yang-Mills theory or
strong coupling regime of (non)-supersymmetric gauge theory with (power-like)
running gauge coupling which depends on curvature. Curvature dependent
quark-antiquark potential is calculated where the geometry type of hyperbolic
(or de Sitter universe) shows (or not) the tendency of the confinement.
Generalization of IIB supergravity background with non-constant axion is
presented. Quark-antiquark potential being again curvature-dependent has a
possibility to produce the standard area law for large separations.Comment: LaTeX file, 24 pages, presentation is improve
Meson Spectroscopy in AdS/CFT with Flavour
We compute the meson spectrum of an N=2 super Yang-Mills theory with
fundamental matter from its dual string theory on AdS_5 x S_5 with a D7-brane
probe. For scalar and vector mesons with arbitrary R-charge the spectrum is
computed in closed form by solving the equations for D7-brane fluctuations; for
matter with non-zero mass m_q it is discrete, exhibits a mass gap of order m_q
/ sqrt(g_s N) and furnishes representations of SO(5) even though the manifest
global symmetry of the theory is only SO(4). The spectrum of mesons with large
spin J is obtained from semiclassical, rotating open strings attached to the
D7-brane. It displays Regge-like behaviour for J << sqrt(g_s N), whereas for J
>> sqrt(g_s N) it corresponds to that of two non-relativistic quarks bound by a
Coulomb potential. Meson interactions, baryons and `giant gauge bosons' are
briefly discussed.Comment: LaTeX, 39 pages, 4 figures, uses epsf. v2: typos corrected.
references adde
Polariton propagation in weak confinement quantum wells
Exciton-polariton propagation in a quantum well, under centre-of-mass
quantization, is computed by a variational self-consistent microscopic theory.
The Wannier exciton envelope functions basis set is given by the simple
analytical model of ref. [1], based on pure states of the centre-of-mass wave
vector, free from fitting parameters and "ad hoc" (the so called additional
boundary conditions-ABCs) assumptions. In the present paper, the former
analytical model is implemented in order to reproduce the centre-of-mass
quantization in a large range of quantum well thicknesses (5a_B < L < inf.).
The role of the dynamical transition layer at the well/barrier interfaces is
discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier
exciton eigenstates are computed, and compared with various theoretical models
with different degrees of accuracy. Exciton-polariton transmission spectra in
large quantum wells (L>> a_B) are computed and compared with experimental
results of Schneider et al.\cite{Schneider} in high quality GaAs samples. The
sound agreement between theory and experiment allows to unambiguously assign
the exciton-polariton dips of the transmission spectrum to the pure states of
the Wannier exciton center-of-mass quantization.Comment: 15 pages, 15 figures; will appear in Phys.Rev.
- âŠ