103,885 research outputs found
Non-Gaussianity from Step Features in the Inflationary Potential
We provide analytic solutions for the power spectrum and bispectrum of
curvature fluctuations produced by a step feature in the inflaton potential,
valid in the limit that the step is short and sharp. In this limit, the
bispectrum is strongly scale dependent and its effective non-linearity attains
a large oscillatory amplitude. The perturbations to the curvature power
spectrum, on the other hand, remain a small component on top of the usual
spectrum of fluctuations generated by slow roll. We utilize our analytic
solutions to assess the observability of the predicted non-Gaussian signatures
and show that, if present, only very sharp steps on scales larger than ~ 2 Gpc
are likely to be able to be detected by Planck. Such features are not only
consistent with WMAP7 data, but can also improve its likelihood by 2 Delta ln L
~ 12 for two extra parameters, the step location and height. If this
improvement were due to a slow roll violating step as considered here, a
bispectrum or corresponding polarization power spectrum detection would provide
definitive checks as to its primordial origin.Comment: Typos fixed, supersedes journal versio
Three-point correlation functions from semiclassical circular strings
The strong-coupling limit of three-point correlation functions of local
operators can be analyzed beyond the supergravity regime using vertex operators
representing spinning string states. When two of the vertex operators
correspond to heavy string states having large quantum numbers, while the third
operator corresponds to a light state with fixed charges, the correlator can be
computed in the large string tension limit by means of a semiclassical
approximation. We study the case when the heavy string states are circular
string solutions with one AdS_5 spin and three different angular momenta along
S^5, for several choices of the light string state.Comment: 13 pages. Latex. v2: Misprints corrected and references adde
Three-point correlators for giant magnons
Three-point correlation functions in the strong-coupling regime of the
AdS/CFT correspondence can be analyzed within a semiclassical approximation
when two of the vertex operators correspond to heavy string states having large
quantum numbers while the third vertex corresponds to a light state with fixed
charges. We consider the case where the heavy string states are chosen to be
giant magnon solitons with either a single or two different angular momenta,
for various different choices of light string states.Comment: 15 pages. Latex. v2: Misprints corrected. Published versio
Beyond the relativistic mean-field approximation: configuration mixing of angular momentum projected wave functions
We report the first study of restoration of rotational symmetry and
fluctuations of the quadrupole deformation in the framework of relativistic
mean-field models. A model is developed which uses the generator coordinate
method to perform configuration mixing calculations of angular momentum
projected wave functions, calculated in a relativistic point-coupling model.
The geometry is restricted to axially symmetric shapes, and the intrinsic wave
functions are generated from the solutions of the constrained relativistic
mean-field + BCS equations in an axially deformed oscillator basis. A number of
illustrative calculations are performed for the nuclei 194Hg and 32Mg, in
comparison with results obtained in non-relativistic models based on Skyrme and
Gogny effective interactions.Comment: 32 pages, 14 figures, submitted to Phys. Rev.
Holographic Correlation Functions for Open Strings and Branes
In this paper, we compute holographically the two-point and three-point
functions of giant gravitons with open strings. We consider the maximal giant
graviton in and the string configurations corresponding to the ground
states of Z=0 and Y=0 open spin chain, and the spinning string in AdS
corresponding to the derivative type impurities in Y=0 or Z=0 open spin chain
as well. We treat the D-brane and open string contribution separately and find
the corresponding D3-brane and string configurations in bulk which connect the
composite operators at the AdS boundary. We apply a new prescription to
treat the string state contribution and find agreements for the two-point
functions. For the three-point functions of two giant gravitons with open
strings and one certain half-BPS chiral primary operator, we find that the
D-brane contributions to structure constant are always vanishing and the open
string contribution for the Y=0 ground state is in perfect match with the
prediction in the free field limit.Comment: 25 page
Magnetoconductance of ballistic chaotic quantum dots: A Brownian motion approach for the -matrix
Using the Fokker-Planck equation describing the evolution of the transmission
eigenvalues for Dyson's Brownian motion ensemble, we calculate the
magnetoconductance of a ballistic chaotic dot in in the crossover regime from
the orthogonal to the unitary symmetry. The correlation functions of the
transmission eigenvalues are expressed in terms of quaternion determinants for
arbitrary number of scattering channels. The corresponding average,
variance and autocorrelation function of the magnetoconductance are given as a
function of the Brownian motion time . A microscopic derivation of this
-Brownian motion approach is discussed and is related to the applied
flux. This exactly solvable random matrix model yields the right expression for
the suppression of the weak localization corrections in the large -limit and
for small applied fluxes. An appropriate rescaling of could extend its
validity to larger magnetic fluxes for the averages, but not for the
correlation functions.Comment: 33 pages, 7 postscript figure
Kinetic theory of point vortices in two dimensions: analytical results and numerical simulations
We develop the kinetic theory of point vortices in two-dimensional
hydrodynamics and illustrate the main results of the theory with numerical
simulations. We first consider the evolution of the system "as a whole" and
show that the evolution of the vorticity profile is due to resonances between
different orbits of the point vortices. The evolution stops when the profile of
angular velocity becomes monotonic even if the system has not reached the
statistical equilibrium state (Boltzmann distribution). In that case, the
system remains blocked in a sort of metastable state with a non standard
distribution. We also study the relaxation of a test vortex in a steady bath of
field vortices. The relaxation of the test vortex is described by a
Fokker-Planck equation involving a diffusion term and a drift term. The
diffusion coefficient, which is proportional to the density of field vortices
and inversely proportional to the shear, usually decreases rapidly with the
distance. The drift is proportional to the gradient of the density profile of
the field vortices and is connected to the diffusion coefficient by a
generalized Einstein relation. We study the evolution of the tail of the
distribution function of the test vortex and show that it has a front
structure. We also study how the temporal auto-correlation function of the
position of the test vortex decreases with time and find that it usually
exhibits an algebraic behavior with an exponent that we compute analytically.
We mention analogies with other systems with long-range interactions
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