869 research outputs found
Phase transition and scaling behavior of topological charged black holes in Horava-Lifshitz gravity
Gravity can be thought as an emergent phenomenon and it has a nice
"thermodynamic" structure. In this context, it is then possible to study the
thermodynamics without knowing the details of the underlying microscopic
degrees of freedom. Here, based on the ordinary thermodynamics, we investigate
the phase transition of the static, spherically symmetric charged black hole
solution with arbitrary scalar curvature in Ho\v{r}ava-Lifshitz gravity at
the Lifshitz point . The analysis is done using the canonical ensemble
frame work; i.e. the charge is kept fixed. We find (a) for both and
, there is no phase transition, (b) while case exhibits the second
order phase transition within the {\it physical region} of the black hole. The
critical point of second order phase transition is obtained by the divergence
of the heat capacity at constant charge. Near the critical point, we find the
various critical exponents. It is also observed that they satisfy the usual
thermodynamic scaling laws.Comment: Minor corrections, refs. added, to appear in Class. Quant. Grav.
arXiv admin note: text overlap with arXiv:1111.0973 by other author
AGN heating, thermal conduction and Sunyaev-Zeldovich effect in galaxy groups and clusters
(abridged) We investigate in detail the role of active galactic nuclei on the
physical state of the gas in galaxy groups and clusters, and the implications
for anisotropy in the CMB from Sunyaev-Zeldovich effect. We include the effect
of thermal conduction, and find that the resulting profiles of temperature and
entropy are consistent with observations. Unlike previously proposed models,
our model predicts that isentropic cores are not an inevitable consequence of
preheating. The model also reproduces the observational trend for the density
profiles to flatten in lower mass systems. We deduce the energy E_agn required
to explain the entropy observations as a function of mass of groups and
clusters M_cl and show that E_agn is proportional to M_cl^alpha with alpha~1.5.
We demonstrate that the entropy measurements, in conjunction with our model,
can be translated into constraints on the cluster--black hole mass relation.
The inferred relation is nonlinear and has the form M_bh\propto M_cl^alpha.
This scaling is an analog and extension of a similar relation between the black
hole mass and the galactic halo mass that holds on smaller scales. We show that
the central decrement of the CMB temperature is reduced due to the enhanced
entropy of the ICM, and that the decrement predicted from the plausible range
of energy input from the AGN is consistent with available data of SZ decrement.
We show that AGN heating, combined with the observational constraints on
entropy, leads to suppression of higher multipole moments in the angular power
spectrum and we find that this effect is stronger than previously thought.Comment: accepted for publication in The Astrophysical Journa
Giant Topological Hall Effect in the Noncollinear Phase of Two-Dimensional Antiferromagnetic Topological Insulator MnBi<sub>4</sub>Te<sub>7</sub>
Magnetic topological insulators provide an important platform for realizing several exotic quantum phenomena, such as the axion insulating state and the quantum anomalous Hall effect, owing to the interplay between topology and magnetism. MnBi4Te7 is a two-dimensional Z(2) antiferromagnetic (AFM) topological insulator with a Ne ' el temperature of similar to 13 K. In AFM materials, the topological Hall effect (THE) is observed owing to the existence of nontrivial spin structures. A material with noncollinearity that develops in the AFM phase rather than at the onset of the AFM order is particularly important. In this study, we observed that such an unanticipated THE starts to develop in a MnBi4Te7 single crystal when the magnetic field is rotated away from the easy axis (c-axis) of the system. Furthermore, the THE resistivity reaches a giant value of similar to 7 mu Omega-cm at 2 K when the angle between the magnetic field and the c-axis is 75 degrees. This value is significantly higher than the values for previously reported systems with noncoplanar structures. The THE can be ascribed to the noncoplanar spin structure resulting from the canted state during the spinflip transition in the ground AFM state of MnBi4Te7. The large THE at a relatively low applied field makes the MnBi4Te7 system a potential candidate for spintronic applications
Symmetries of Snyder--de Sitter space and relativistic particle dynamics
We study the deformed conformal-Poincare symmetries consistent with the
Snyder--de Sitter space. A relativistic particle model invariant under these
deformed symmetries is given. This model is used to provide a gauge independent
derivation of the Snyder--de Sitter algebra. Our results are valid in the
leading order in the parameters appearing in the model.Comment: 12 pages, LaTeX, version appearing in JHEP, minor changes to match
published versio
Valence bond solid formalism for d-level one-way quantum computation
The d-level or qudit one-way quantum computer (d1WQC) is described using the
valence bond solid formalism and the generalised Pauli group. This formalism
provides a transparent means of deriving measurement patterns for the
implementation of quantum gates in the computational model. We introduce a new
universal set of qudit gates and use it to give a constructive proof of the
universality of d1WQC. We characterise the set of gates that can be performed
in one parallel time step in this model.Comment: 26 pages, 9 figures. Published in Journal of Physics A: Mathematical
and Genera
Analytic study of Gauss-Bonnet holographic superconductors in Born-Infeld electrodynamics
Using Sturm-Liouville (SL) eigenvalue problem, we investigate several
properties of holographic s-wave superconductors in Gauss-Bonnet gravity with
Born-Infeld electrodynamics in the probe limit. Our analytic scheme has been
found to be in good agreement with the numerical results. From our analysis it
is quite evident that the scalar hair formation at low temperatures is indeed
affected by both the Gauss-Bonnet as well as the Born-Infeld coupling
parameters. We also compute the critical exponent associated with the
condensation near the critical temperature. The value of the critical exponent
thus obtained indeed suggests a universal mean field behavior.Comment: 9 pages, Latex, minor modifications, To appear in JHE
Analytic study of properties of holographic p-wave superconductors
In this paper, we analytically investigate the properties of p-wave
holographic superconductors in -Schwarzschild background by two
approaches, one based on the Sturm-Liouville eigenvalue problem and the other
based on the matching of the solutions to the field equations near the horizon
and near the asymptotic region. The relation between the critical
temperature and the charge density has been obtained and the dependence of the
expectation value of the condensation operator on the temperature has been
found. Our results are in very good agreement with the existing numerical
results. The critical exponent of the condensation also comes out to be 1/2
which is the universal value in the mean field theory.Comment: Latex, To appear in JHE
Probing galaxy evolution through HI 21-cm emission and absorption: current status and prospects with the Square Kilometre Array
One of the major science goals of the Square Kilometre Array (SKA) is to
understand the role played by atomic hydrogen (HI) gas in the evolution of
galaxies throughout cosmic time. The hyperfine transition line of the hydrogen
atom at 21-cm is one of the best tools to detect and study the properties of HI
gas associated with galaxies. In this article, we review our current
understanding of HI gas and its relationship with galaxies through observations
of the 21-cm line both in emission and absorption. In addition, we provide an
overview of the HI science that will be possible with SKA and its pre-cursors
and pathfinders, i.e. HI 21-cm emission and absorption studies of galaxies from
nearby to high redshifts that will trace various processes governing galaxy
evolution.Comment: 31 pages, 7 figures, accepted on 27 May 2022 for publication in the
Journal of Astrophysics and Astronomy (to appear in the special issue on
"Indian participation in the SKA"), figure 4 has been update
Pauli Diagonal Channels Constant on Axes
We define and study the properties of channels which are analogous to unital
qubit channels in several ways. A full treatment can be given only when the
dimension d is a prime power, in which case each of the (d+1) mutually unbiased
bases (MUB) defines an axis. Along each axis the channel looks like a
depolarizing channel, but the degree of depolarization depends on the axis.
When d is not a prime power, some of our results still hold, particularly in
the case of channels with one symmetry axis. We describe the convex structure
of this class of channels and the subclass of entanglement breaking channels.
We find new bound entangled states for d = 3.
For these channels, we show that the multiplicativity conjecture for maximal
output p-norm holds for p=2. We also find channels with behavior not exhibited
by unital qubit channels, including two pairs of orthogonal bases with equal
output entropy in the absence of symmetry. This provides new numerical evidence
for the additivity of minimal output entropy
Controlling passively-quenched single photon detectors by bright light
Single photon detectors based on passively-quenched avalanche photodiodes can
be temporarily blinded by relatively bright light, of intensity less than a
nanowatt. I describe a bright-light regime suitable for attacking a quantum key
distribution system containing such detectors. In this regime, all single
photon detectors in the receiver Bob are uniformly blinded by continuous
illumination coming from the eavesdropper Eve. When Eve needs a certain
detector in Bob to produce a click, she modifies polarization (or other
parameter used to encode quantum states) of the light she sends to Bob such
that the target detector stops receiving light while the other detector(s)
continue to be illuminated. The target detector regains single photon
sensitivity and, when Eve modifies the polarization again, produces a single
click. Thus, Eve has full control of Bob and can do a successful
intercept-resend attack. To check the feasibility of the attack, 3 different
models of passively-quenched detectors have been tested. In the experiment, I
have simulated the intensity diagrams the detectors would receive in a real
quantum key distribution system under attack. Control parameters and side
effects are considered. It appears that the attack could be practically
possible.Comment: Experimental results from a third detector model added. Minor
corrections and edits made. 11 pages, 10 figure
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