533 research outputs found
Disordered Systems and the Replica Method in AdS/CFT
We formulate a holographic description of effects of disorder in conformal
field theories based on the replica method and the AdS/CFT correspondence.
Starting with copies of conformal field theories, randomness with a
gaussian distribution is described by a deformation of double trace operators.
After computing physical quantities, we take the limit at the final
step. We compute correlation functions in the disordered systems by using the
holographic replica method as well as the formulation in the conformal field
theory. We find examples where disorder changes drastically the scaling of two
point functions. The renormalization group flow of the effective central charge
in our disordered systems is also discussed.Comment: 26 pages, references added, published versio
On String Theory Duals of Lifshitz-like Fixed Points
We present type IIB supergravity solutions which are expected to be dual to
certain Lifshitz-like fixed points with anisotropic scale invariance. They are
expected to describe a class of D3-D7 systems and their finite temperature
generalizations are straightforward. We show that there exist solutions that
interpolate between these anisotropic solutions in the IR and the standard AdS5
solutions in the UV. This predicts anisotropic RG flows from familiar isotropic
fixed points to anisotropic ones. In our case, these RG flows are triggered by
a non-zero theta-angle in Yang-Mills theories that linearly depends on one of
the spatial coordinates. We study the perturbations around these backgrounds
and discuss the possibility of instability. We also holographically compute
their thermal entropies, viscosities, and entanglement entropies.Comment: 47 pages, 4 figure
A family of super Schrodinger invariant Chern-Simons matter systems
We investigate non-relativistic limits of the N=3 Chern-Simons matter system
in 1+2 dimensions. The relativistic theory can generate several inequivalent
super Schodinger invariant theories, depending on the degrees of freedom we
choose to retain in the non-relativistic limit. The maximally supersymmetric
Schrodinger invariant theory is obtained by keeping all particle degrees of
freedom. The other descendants, where particles and anti-particles coexist, are
also Schrodinger invariant but preserve less supersymmetries. Thus, we have a
family of super Schrodinger invariant field theories produced from the parent
relativistic theory.Comment: 1+35 pages, references added and typos fixe
Spin-current induced electric field
We theoretically predict that a pure steady state spin-current without
charge-current can induce an electric field. A formula for the induced electric
field is derived and we investigate its characteristics. Conversely, a moving
spin is affected by an external electric field and we present a formula for the
interaction energy.Comment: 4 pages, 2 figure
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
The Klebanov-Strassler model with massive dynamical flavors
We present a fully backreacted D3-D7 supergravity solution dual to the
Klebanov-Strassler cascading gauge theory coupled to a large number of massive
dynamical flavors in the Veneziano limit. The mass of the flavors can be larger
or smaller than the dynamically generated scale. The solution is always regular
at the origin of the radial coordinate and as such it can be suitably employed
to explore the rich IR physics of the dual gauge theory. In this paper we focus
on the static quark-antiquark potential, the screening of chromoelectric
charges induced by the dynamical flavors, the flux tube breaking and the mass
spectrum of the first mesonic excitations. Moreover, we discuss the occurrence
of quantum phase transitions in the connected part of the static
quark-antiquark potential. Depending on the ratio of certain parameters, like
the flavor mass, with respect to some critical values, we find a discontinuous
(first order) or smooth transition from a Coulomb-like to a linear phase. We
evaluate the related critical exponents finding that they take classical
mean-field values and argue that this is a universal feature of analogous first
order transitions occurring in the static potential for planar gauge theories
having a dual supergravity description.Comment: 31 pages + appendices, 13 figures; v2: added comments in sections 3.4
and 4.2, small changes in section 5.2, typos corrected in eq. 6.6, references
adde
Formation of stars and planets: the role of magnetic fields
Star formation is thought to be triggered by gravitational collapse of the
dense cores of molecular clouds. Angular momentum conservation during the
collapse results in the progressive increase of the centrifugal force, which
eventually halts the inflow of material and leads to the development of a
central mass surrounded by a disc. In the presence of an angular momentum
transport mechanism, mass accretion onto the central object proceeds through
this disc, and it is believed that this is how stars typically gain most of
their mass. However, the mechanisms responsible for this transport of angular
momentum are not well understood. Although the gravitational field of a
companion star or even gravitational instabilities (particularly in massive
discs) may play a role, the most general mechanisms are turbulence viscosity
driven by the magnetorotational instability (MRI), and outflows accelerated
centrifugally from the surfaces of the disc. Both processes are powered by the
action of magnetic fields and are, in turn, likely to strongly affect the
structure, dynamics, evolutionary path and planet-forming capabilities of their
host discs. The weak ionisation of protostellar discs, however, may prevent the
magnetic field from effectively coupling to the gas and shear and driving these
processes. Here I examine the viability and properties of these
magnetically-driven processes in protostellar discs. The results indicate that,
despite the weak ionisation, the magnetic field is able to couple to the gas
and shear for fluid conditions thought to be satisfied over a wide range of
radii in these discs.Comment: Invited Review. 11 figures and 1 table. Accepted for publication in
Astrophysics & Space Scienc
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions
Solid solutions of (1-x)LaFeO3-(x)PbTiO3 (0<x<1) have been prepared by
conventional solid-state reaction. These complex perovskites have been studied
by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented
with dielectric, magnetic, heat capacity and M\"ossbauer measurements. Complete
solubility in the perovskite series was demonstrated. The NPD and XRPD patterns
were successfully refined as orthorhombic (x \leq 0.7) and tetragonal (x \geq
0.8). A composition-driven phase transformation occurs within the interval
0.7<x<0.8. The samples with x<0.5 showed evidence of long-range magnetic
ordering with an G-type antiferromagnetic arrangement of the magnetic moments
of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on
the obtained experimental data, a combined structural and magnetic phase
diagram has been constructed. The factors governing the structural, dielectric
and magnetic properties of (1-x) LaFeO3 - (x)PbTiO3 solid solutions are
discussed, as well as their possible multiferroicity.Comment: 33 pages, 15 figure
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