586 research outputs found
Phase structure of black branes in grand canonical ensemble
This is a companion paper of our previous work [1] where we studied the
thermodynamics and phase structure of asymptotically flat black -branes in a
cavity in arbitrary dimensions in a canonical ensemble. In this work we
study the thermodynamics and phase structure of the same in a grand canonical
ensemble. Since the boundary data in two cases are different (for the grand
canonical ensemble boundary potential is fixed instead of the charge as in
canonical ensemble) the stability analysis and the phase structure in the two
cases are quite different. In particular, we find that there exists an analog
of one-variable analysis as in canonical ensemble, which gives the same
stability condition as the rather complicated known (but generalized from black
holes to the present case) two-variable analysis. When certain condition for
the fixed potential is satisfied, the phase structure of charged black
-branes is in some sense similar to that of the zero charge black -branes
in canonical ensemble up to a certain temperature. The new feature in the
present case is that above this temperature, unlike the zero-charge case, the
stable brane phase no longer exists and `hot flat space' is the stable phase
here. In the grand canonical ensemble there is an analog of Hawking-Page
transition, even for the charged black -brane, as opposed to the canonical
ensemble. Our study applies to non-dilatonic as well as dilatonic black
-branes in space-time dimensions.Comment: 32 pages, 2 figures, various points refined, discussion expanded,
references updated, typos corrected, published in JHEP 1105:091,201
Disambiguating brain functional connectivity
Functional connectivity (FC) analyses of correlations of neural activity are used extensively in neuroimaging and electrophysiology to gain insights into neural interactions. However, analyses assessing changes in correlation fail to distinguish effects produced by sources as different as changes in neural signal amplitudes or noise levels. This ambiguity substantially diminishes the value of FC for inferring system properties and clinical states. Network modelling approaches may avoid ambiguities, but require specific assumptions. We present an enhancement to FC analysis with improved specificity of inferences, minimal assumptions and no reduction in flexibility. The Additive Signal Change (ASC) approach characterizes FC changes into certain prevalent classes of signal change that involve the input of additional signal to existing activity. With FMRI data, the approach reveals a rich diversity of signal changes underlying measured changes in FC, suggesting that it could clarify our current understanding of FC changes in many contexts. The ASC method can also be used to disambiguate other measures of dependency, such as regression and coherence, providing a flexible tool for the analysis of neural data
Supermembrane interaction with dynamical D=4 N=1 supergravity. Superfield Lagrangian description and spacetime equations of motion
We obtain the complete set of equations of motion for the interacting system
of supermembrane and dynamical D=4 N = 1 supergravity by varying its complete
superfield action and writing the resulting superfield equations in the special
gauge where the supermembrane Goldstone field is set to zero. We solve the
equations for auxiliary fields and discuss the effect of dynamical generation
of cosmological constant in the Einstein equation of interacting system and its
renormalization due to some regular contributions from supermembrane. These two
effects (discussed in late 70th and 80th, in the bosonic perspective and in the
supergravity literature) result in that, generically, the cosmological constant
has different values in the branches of the spacetime separated by the
supermembrane worldvolume.Comment: 23 pages, no figures. V2 two references added, 24 page
Black Holes in Gravity with Conformal Anomaly and Logarithmic Term in Black Hole Entropy
We present a class of exact analytic and static, spherically symmetric black
hole solutions in the semi-classical Einstein equations with Weyl anomaly. The
solutions have two branches, one is asymptotically flat and the other
asymptotically de Sitter. We study thermodynamic properties of the black hole
solutions and find that there exists a logarithmic correction to the well-known
Bekenstein-Hawking area entropy. The logarithmic term might come from non-local
terms in the effective action of gravity theories. The appearance of the
logarithmic term in the gravity side is quite important in the sense that with
this term one is able to compare black hole entropy up to the subleading order,
in the gravity side and in the microscopic statistical interpretation side.Comment: Revtex, 10 pages. v2: minor changes and to appear in JHE
Trace anomalies in chiral theories revisited
Motivated by the search for possible CP violating terms in the trace of the
energy-momentum tensor in theories coupled to gravity we revisit the problem of trace
anomalies in chiral theories. We recalculate the latter and ascertain that in the trace of
the energy-momentum tensor of theories with chiral fermions at one-loop the Pontryagin
density appears with an imaginary coefficient. We argue that this may break unitarity, in
which case the trace anomaly has to be used as a selective criterion for theories, analogous
to the chiral anomalies in gauge theories. We analyze some remarkable consequences of
this fact, that seem to have been overlooked in the literature
On duality symmetry in perturbative quantum theory
Non-compact symmetries of extended 4d supergravities involve duality
rotations of vectors and thus are not manifest off-shell invariances in
standard "second-order" formulation. To study how such symmetries are realised
in the quantum theory we consider examples in 2 dimensions where vector-vector
duality is replaced by scalar-scalar one. Using a "doubled" formulation, where
fields and their momenta are treated on an equal footing and the duality
becomes a manifest symmetry of the action (at the expense of Lorentz symmetry),
we argue that the corresponding on-shell quantum effective action or S-matrix
are duality symmetric as well as Lorentz invariant. The simplest case of
discrete Z_2 duality corresponds to a symmetry of the S-matrix under flipping
the sign of the negative-chirality scalars in 2 dimensions or phase rotations
of chiral (definite-helicity) parts of vectors in 4 dimensions. We also briefly
discuss some 4d models and comment on implications of our analysis for extended
supergravities.Comment: 21 pages, Latex v2: comments and references added v3: references and
minor comments adde
Classification of non-Riemannian doubled-yet-gauged spacetime
Assuming covariant fields as the `fundamental' variables,
Double Field Theory can accommodate novel geometries where a Riemannian metric
cannot be defined, even locally. Here we present a complete classification of
such non-Riemannian spacetimes in terms of two non-negative integers,
, . Upon these backgrounds, strings become
chiral and anti-chiral over and directions respectively, while
particles and strings are frozen over the directions. In
particular, we identify as Riemannian manifolds, as
non-relativistic spacetime, as Gomis-Ooguri non-relativistic string,
as ultra-relativistic Carroll geometry, and as Siegel's
chiral string. Combined with a covariant Kaluza-Klein ansatz which we further
spell, leads to Newton-Cartan gravity. Alternative to the conventional
string compactifications on small manifolds, non-Riemannian spacetime such as
, may open a new scheme of the dimensional reduction from ten to
four.Comment: 1+41 pages; v2) Refs added; v3) Published version; v4) Sign error in
(2.51) correcte
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Health-related quality of life in Huntingtonâs Disease patients: a comparison of proxy assessment and patient self-rating using the disease-specific Huntingtonâs Disease health-related quality of life questionnaire (HDQoL)
Huntingtonâs disease (HD) is a fatal, neurodegenerative disease for which there is no known cure. Proxy evaluation is relevant for HD as its manifestation might limit the ability of persons to report their health-related quality of life (HrQoL). This study explored patientâproxy ratings of HrQoL of persons at different stages of HD, and examined factors that may affect proxy ratings. A total of 105 patientâproxy pairs completed the Huntingtonâs disease health-related quality of life questionnaire (HDQoL) and other established HrQoL measures (EQ-5D and SF-12v2). Proxyâpatient agreement was assessed in terms of absolute level (mean ratings) and intraclass correlation. Proxiesâ ratings were at a similar level to patientsâ self-ratings on an overall Summary Score and on most of the six Specific Scales of the HDQoL. On the Specific Hopes and Worries Scale, proxies on average rated HrQoL as better than patientsâ self-ratings, while on both the Specific Cognitive Scale and Specific Physical and Functional Scale proxies tended to rate HrQoL more poorly than patients themselves. The patientâs disease stage and mental wellbeing (SF-12 Mental Component scale) were the two factors that primarily affected proxy assessment. Proxy scores were strongly correlated with patientsâ self-ratings of HrQoL, on the Summary Scale and all Specific Scales. The patientâproxy correlation was lower for patients at moderate stages of HD compared to patients at early and advanced stages. The proxy report version of the HDQoL is a useful complementary tool to self-assessment, and a promising alternative when individual patients with advanced HD are unable to self-report
D=3, N=8 conformal supergravity and the Dragon window
We give a superspace description of D=3, N=8 supergravity. The formulation is
off-shell in the sense that the equations of motion are not implied by the
superspace constraints (but an action principle is not given). The multiplet
structure is unconventional, which we connect to the existence of a "Dragon
window", that is modules occurring in the supercurvature but not in the
supertorsion. According to Dragon's theorem this cannot happen above three
dimensions. We clarify the relevance of this window for going on the conformal
shell, and discuss some aspects of coupling to conformal matter.Comment: plain tex, 24 pp v2: minor change
Spin-2 spectrum of defect theories
We study spin-2 excitations in the background of the recently-discovered
type-IIB solutions of D'Hoker et al. These are holographically-dual to defect
conformal field theories, and they are also of interest in the context of the
Karch-Randall proposal for a string-theory embedding of localized gravity. We
first generalize an argument by Csaki et al to show that for any solution with
four-dimensional anti-de Sitter, Poincare or de Sitter invariance the spin-2
excitations obey the massless scalar wave equation in ten dimensions. For the
interface solutions at hand this reduces to a Laplace-Beltrami equation on a
Riemann surface with disk topology, and in the simplest case of the
supersymmetric Janus solution it further reduces to an ordinary differential
equation known as Heun's equation. We solve this equation numerically, and
exhibit the spectrum as a function of the dilaton-jump parameter .
In the limit of large a nearly-flat linear-dilaton dimension grows
large, and the Janus geometry becomes effectively five-dimensional. We also
discuss the difficulties of localizing four-dimensional gravity in the more
general backgrounds with NS5-brane or D5-brane charge, which will be analyzed
in detail in a companion paper.Comment: 41 pages, 6 figure
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