74 research outputs found
On Black Hole Stability in Critical Gravities
We consider extended cosmological gravities with Ricci tensor and scalar
squared terms in diverse dimensions. These theories admit solutions of Einstein
metrics, including the Schwarzschild-Tangherlini AdS black holes, whose mass
and entropy vanish at the critical point. We perform linearized analysis around
the black holes and show that in general the spectrum consists of the usual
spin-2 massless and ghost massive modes. We demonstrate that there is no
exponentially-growing tachyon mode in the black holes. At the critical point,
the massless spin-2 modes have zero energy whilst the massive spin-2 modes are
replaced by the log modes. There always exist certain linear combination of
massless and log modes that has negative energy. Thus the stability of the
black holes requires that the log modes to be truncated out by the boundary
condition.Comment: 16 pages, minor corrections, further comments and references adde
Gauged Kaluza-Klein AdS Pseudo-supergravity
We obtain the pseudo-supergravity extension of the D-dimensional Kaluza-Klein
theory, which is the circle reduction of pure gravity in D+1 dimensions. The
fermionic partners are pseudo-gravitino and pseudo-dilatino. The full
Lagrangian is invariant under the pseudo-supersymmetric transformation, up to
quadratic order in fermion fields. We find that the theory possesses a U(1)
global symmetry that can be gauged so that all the fermions are charged under
the Kaluza-Klein vector. The gauging process generates a scalar potential that
has a maximum, leading to the AdS vacuum. Whist the highest dimension for
gauged AdS supergravity is seven, our gauged AdS pseudo-supergravities can
exist in arbitrary dimensions.Comment: Latex, 13 pages, typos corrected, version in PL
Critical Points of D-Dimensional Extended Gravities
We study the parameter space of D-dimensional cosmological Einstein gravity
together with quadratic curvature terms. In D>4 there are in general two
distinct (anti)-de Sitter vacua. We show that for appropriate choice of the
parameters there exists a critical point for one of the vacua, for which there
are only massless tensor, but neither massive tensor nor scalar, gravitons. At
criticality, the linearized excitations have vanishing energy (as do black hole
solutions). A further restriction of the parameters gives a one-parameter
cosmological Einstein plus Weyl^2 model with a unique vacuum, whose \Lambda is
determined.Comment: 6 pages, typos correcte
Leading-Order Actions of Goldstino Fields
This paper starts with a self-contained discussion of the so-called
Akulov-Volkov action S_AV, which is traditionally taken to be the leading-order
action of Goldstino field. Explicit expressions for S_AV and its chiral version
S_AV^ch are presented. We then turn to the issue on how these actions are
related to the leading-order action S_NL proposed in the newly proposed
constrained superfield formalism. We show that S_NL may yield S_AV/S_AV^ch or a
totally different action S_KS, depending on how the auxiliary field in the
former is integrated out. However, S_KS and S_AV/S_AV^ch always yield the same
S-matrix elements, as one would have expected from general considerations in
quantum field theory.Comment: Minor changes, version to appear in European Physical Journal
f(R) Theories of Supergravities and Pseudo-supergravities
We present f(R) theories of ten-dimensional supergravities, including the
fermionic sector up to the quadratic order in fermion fields. They are obtained
by performing the conformal scaling on the usual supergravities to the f(R)
frame in which the dilaton becomes an auxiliary field and can be integrated
out. The f(R) frame coincides with that of M-theory, D2-branes or NS-NS
5-branes. We study various BPS p-brane solutions and their near-horizon AdS
\times sphere geometries in the context of the f(R) theories. We find that new
solutions emerge with global structures that do not exist in the corresponding
solutions of the original supergravity description. In lower dimensions, We
construct the f(R) theory of N=2, D=5 gauged supergravity with a vector
multiplet, and that for the four-dimensional U(1)^4 gauged theory with three
vector fields set equal. We find that some previously-known BPS singular
"superstars" become wormholes in the f(R) theories. We also construct a large
class of f(R) (gauged) pseudo-supergravities. In addition we show that the
breathing mode in the Kaluza-Klein reduction of Gauss-Bonnet gravity on S^1 is
an auxiliary field and can be integrated out.Comment: Latex, 46 page
f(R) Gravities, Killing Spinor Equations, "BPS" Domain Walls and Cosmology
We derive the condition on f(R) gravities that admit Killing spinor equations
and construct explicit such examples. The Killing spinor equations can be used
to reduce the fourth-order differential equations of motion to the first order
for both the domain wall and FLRW cosmological solutions. We obtain exact "BPS"
domain walls that describe the smooth Randall-Sundrum II, AdS wormholes and the
RG flow from IR to UV. We also obtain exact smooth cosmological solutions that
describe the evolution from an inflationary starting point with a larger
cosmological constant to an ever-expanding universe with a smaller cosmological
constant. In addition, We find exact smooth solutions of pre-big bang models,
bouncing or crunching universes. An important feature is that the scalar
curvature R of all these metrics is varying rather than a constant. Another
intriguing feature is that there are two different f(R) gravities that give
rise to the same "BPS" solution. We also study linearized f(R) gravities in
(A)dS vacua.Comment: 37 pages, discussion on gravity trapping in RSII modified, typos
corrected, further comments and references added; version to appear in JHE
Thermodynamical Metrics and Black Hole Phase Transitions
An important phase transition in black hole thermodynamics is associated with
the divergence of the specific heat with fixed charge and angular momenta, yet
one can demonstrate that neither Ruppeiner's entropy metric nor Weinhold's
energy metric reveals this phase transition. In this paper, we introduce a new
thermodynamical metric based on the Hessian matrix of several free energy. We
demonstrate, by studying various charged and rotating black holes, that the
divergence of the specific heat corresponds to the curvature singularity of
this new metric. We further investigate metrics on all thermodynamical
potentials generated by Legendre transformations and study correspondences
between curvature singularities and phase transition signals. We show in
general that for a system with n-pairs of intensive/extensive variables, all
thermodynamical potential metrics can be embedded into a flat (n,n)-dimensional
space. We also generalize the Ruppeiner metrics and they are all conformal to
the metrics constructed from the relevant thermodynamical potentials.Comment: Latex, 25 pages, reference added, typos corrected, English polished
and the Hawking-Page phase transition clarified; to appear in JHE
Duality in Binocular Rivalry: Distinct Sensitivity of Percept Sequence and Percept Duration to Imbalance between Monocular Stimuli
Visual perception is usually stable and accurate. However, when the two eyes are simultaneously presented with conflicting stimuli, perception falls into a sequence of spontaneous alternations, switching between one stimulus and the other every few seconds. Known as binocular rivalry, this visual illusion decouples subjective experience from physical stimulation and provides a unique opportunity to study the neural correlates of consciousness. The temporal properties of this alternating perception have been intensively investigated for decades, yet the relationship between two fundamental properties - the sequence of percepts and the duration of each percept - remains largely unexplored
Effects of 15-Deoxy-Δ12,14-Prostaglandin J2 (15d-PGJ2) and Rosiglitazone on Human Vδ2+ T Cells
BACKGROUND:Thiazolidinediones (TZD) class of drugs, and 15-deoxy-D12,14-prostaglandin J2 (15d-PGJ2) are immune regulators predicted to modulate human autoimmune disease. Their effects on gammadelta T cells, which are involved in animal model and human and animal autoimmune diseases, are unknown. METHODOLOGY/PRINCIPAL FINDINGS:We characterized the activity of rosiglitazone (from the TZD class of drugs) and 15d-PGJ2 in human Vdelta2 T cells. We found that 15d-PGJ2 and rosiglitazone had different effects on Vdelta2 T cell functions. Both 15d-PGJ2 and rosiglitazone suppressed Vdelta2 T cell proliferation in response to IPP and IL2. However, only 15d-PGJ2 suppressed functional responses including cytokine production, degranulation and cytotoxicity against tumor cells. The mechanism for 15d-PGJ2 effects on Vdelta2 T cells acts through inhibiting Erk activation. In contrast, rosiglitazone did not affect Erk activation but the IL2 signaling pathway, which accounts for rosiglitazone suppression of IL2-dependent, Vdelta2 T cell proliferation without affecting TCR-dependent functions. Rosiglitazone and 15d-PGJ2 are designed to be peroxisome proliferator-activated receptor gamma (PPARgamma) ligands and PPARgamma was expressed in Vdelta2 T cell. Surprisingly, when PPARgamma levels were lowered by specific siRNA, 15d-PGJ2 and rosiglitazone were still active, suggesting their target of action induces cellular proteins other than PPARgamma. CONCLUSIONS/SIGNIFICANCE:The current findings expand our understanding of how the immune system is regulated by rosiglitazone and 15d-PGJ2 and will be important to evaluate these compounds as therapeutic agents in human autoimmune disease
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