11,756 research outputs found
S-duality in AdS/CFT magnetohydrodynamics
We study the nonlinear hydrodynamics of a 2+1 dimensional charged conformal
fluid subject to slowly varying external electric and magnetic fields.
Following recent work on deriving nonlinear hydrodynamics from gravity, we
demonstrate how long wavelength perturbations of the AdS dyonic black brane
solution of 4D supergravity are governed by equations equivalent to fluid
dynamics equations in the boundary theory. We investigate the implications of
-duality for our system, and derive restrictions imposed on the transport
coefficients of a generic fluid invariant under the S operation. We also expand
on our earlier work and determine a new set of previously undetermined
transport coefficients for the conformal fluid with an AdS gravity dual. Quite
surprisingly, we discover that half of the transport coefficients allowed by
symmetry vanish in the holographic fluid at linear order in the hydrodynamic
expansion.Comment: 25 page
Nonlinear Magnetohydrodynamics from Gravity
We apply the recently established connection between nonlinear fluid dynamics
and AdS gravity to the case of the dyonic black brane in AdS_4. This yields the
equations of fluid dynamics for a 2+1 dimensional charged fluid in a background
magnetic field. We construct the gravity solution to second order in the
derivative expansion. From this we find the fluid dynamical stress tensor and
charge current to second and third order in derivatives respectively, along
with values for the associated transport coefficients.Comment: 20 pages. v3: Added section 2.3 on comparison to other approaches and
definition of viscosit
Discovery of a remarkable subpulse drift pattern in PSR B0818-41
We report the discovery of a remarkable subpulse drift pattern in the
relatively less studied wide profile pulsar, B0818-41, using high sensitivity
GMRT observations. We find simultaneous occurrence of three drift regions with
two different drift rates: an inner region with steeper apparent drift rate
flanked on each side by a region of slower apparent drift rate. Furthermore,
these closely spaced drift bands always maintain a constant phase relationship.
Though these drift regions have significantly different values for the measured
P2, the measured P3 value is the same and equal to 18.3 P1. We interpret the
unique drift pattern of this pulsar as being created by the intersection of our
line of sight (LOS) with two conal rings on the polar cap of a fairly aligned
rotator (inclination angle alpha ~ 11 deg), with an ``inner'' LOS geometry
(impact angle beta ~ -5.4 deg). We argue that both the rings have the same
values for the carousel rotation periodicity P4 and the number of sparks Nsp.
We find that Nsp is 19-21 and show that it is very likely that, P4 is the same
as the measured P3, making it a truly unique pulsar. We present results from
simulations of the radiation pattern using the inferred parameters, that
support our interpretations and reproduce the average profile as well as the
observed features in the drift pattern quite well.Comment: 5 pages and 7 figures, Accepted for publication in MNRAS Letter
Limits to the Mass and the Radius of the Compact Star in SAX J1808.4--3658 and Their Implications
We show that a survey of equations of state and observations of X-ray
pulsations from SAX J1808.4-3658 give 2.27 solar mass as the upper limit of the
compact star mass. The corresponding upper limit of the radius comes out to be
9.73 km. We also do a probabilistic study to estimate the lower limit of the
mass of the compact star. Such a limit puts useful constraints on equations of
state. We also discuss the implications of the upper mass limit for the the
evolutionary history of the source, as well as the detection of it in radio
frequencies. We envisage that the possible observation of radio-eclipse may be
able to rule out several soft equation of state models, by setting a moderately
high value for the lower limit of inclination angle.Comment: 7 pages, 1 table, 2 figures, accepted for publication in ApJ Letter
Energy dependent wavelength of the ion induced nanoscale ripple
Wavelength variation of ion beam induced nanoscale ripple structure has
received much attention recently due to its possible application in
nanotechnology. We present here results of Ar bombarded Si in the energy
range 50 to 140 keV to demonstrate that with beam scanning the ripple
wavelength increases with ion energy and decreases with energy for irradiation
without ion beam scanning. An expression for the energy dependence of ripple
wavelength is proposed taking into simultaneous effect of thermally activated
surface diffusion and ion induced effective surface diffusion.Comment: REVTeX (4 pages), 3 EPS figure
Instantons and Entanglement Entropy
We would like to put the area law -- believed to by obeyed by entanglement
entropies in the ground state of a local field theory -- to scrutiny in the
presence of non-perturbative effects. We study instanton corrections to
entanglement entropy in various models whose instanton effects are well
understood, including gauge theory in 2+1 dimensions and false vacuum
decay in theory, and we demonstrate that the area law is indeed obeyed
in these models. We also perform numerical computations for toy wavefunctions
mimicking the theta vacuum of the (1+1)-dimensional Schwinger model. Our
results indicate that such superpositions exhibit no more violation of the area
law than the logarithmic behavior of a single Fermi surface.Comment: 29 pages, 4 figures, typos corrected, substantially revised,
published versio
Effect of Epitaxial Strain on Phase Separation in Thin Films
We examine the role of an imposed epitaxial strain e in enhancing or
depressing the spinodal instability of an alloy thin film. Since the alloy film
starts with an imposed strain, phase separation offers a mechanism to relieve
it, but only when the film is elastically inhomogeneous. With
composition-dependence of elastic modulus given by y, and that of lattice
parameter by {\eta}, our simulations using the Cahn-Hilliard model show (and
analytical results for early stages confirm) that, for (ey/{\eta}) > 0, the
imposed strain adds to the driving force for phase separation, decreases the
maximally growing wave length, and expands the coherent spinodal in the phase
diagram. Further, when (ey/{\eta}) > 0.372, it expands to even outside of
chemical spinodal. Phase separation produces islands of elastically softer
(harder) phase with (without) a favorable imposed strain. These results are in
agreement with experimental results in GeSi thin films on Si and Ge substrates,
as well as in InGaAs films on GaAs substrates.Comment: 4 pages, 3 figure
Scalar sector properties of two-Higgs-doublet models with a global U(1) symmetry
We analyze the scalar sector properties of a general class of
two-Higgs-doublet models which has a global U(1) symmetry in the quartic terms.
We find constraints on the parameters of the potential from the considerations
of unitarity of scattering amplitudes, the global stability of the potential
and the -parameter. We concentrate on the spectrum of the non-standard
scalar masses in the decoupling limit which is preferred by the Higgs data at
the LHC. We exhibit charged-Higgs induced contributions to the diphoton decay
width of the 125\,GeV Higgs boson and its correlation with the corresponding
width.Comment: 12 pages, 15 eps figure files; minor modifications made and a few
references adde
Gauge/Gravity Duality and Some Applications
We discuss the AdS/CFT correspondence in which space-time emerges from an
interacting theory of D-branes and open strings. These ideas have a historical
continuity with QCD which is an interacting theory of quarks and gluons. In
particular we review the classic case of D3 branes and the non-conformal D1
brane system. We outline by some illustrative examples the calculations that
are enabled in a strongly coupled gauge theory by correspondence with dynamical
horizons in semi-classical gravity in one higher dimension. We also discuss
implications of the gauge-fluid/gravity correspondence for the information
paradox of black hole physics.Comment: 19 pages, 2 figures, Contribution to "Conference in Honor of Murray
Gell-Mann's 80th Birthday
A Note on the Deformation of a Rotating Inhomogeneous Piezoelectric Thick Disc
The Equations of Elasticity, The Maxwell's Electro-mechanical Equations and the Constltutive
Equations of Piezoelectricity Have Been Made Use of in Solving the Problem. The Results
Arrived at Essentially Agree With the Results Known for Aeolotropic Media and Which Are
Free From Piezoelectric Excilations
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