623 research outputs found
Black Hole Thermodynamics and Massive Gravity
We consider the generalized laws of thermodynamics in massive gravity. Making
use of explicit black hole solutions, we devise black hole merger processes in
which i) total entropy of the system decreases ii) the zero-temperature
extremal black hole is created. Thus, both second and third laws of
thermodynamics are violated. In both cases, the violation can be traced back to
the presence of negative-mass black holes, which, in turn, is related to the
violation of the null energy condition. The violation of the third law of
thermodynamics implies, in particular, that a naked singularity may be created
as a result of the evolution of a singularity-free state. This may signal a
problem in the model, unless the creation of the negative-mass black holes from
positive-mass states can be forbidden dynamically or the naked singularity may
somehow be resolved in a full quantum theory.Comment: 15 pages, 4 figures; v2:Style changed to JHEP. Discussion added in
the conclusions. Revised version to match published versio
Massive Gravity: Exorcising the Ghost
We consider Higgs massive gravity [1,2] and investigate whether a nonlinear
ghost in this theory can be avoided. We show that although the theory
considered in [10,11] is ghost free in the decoupling limit, the ghost
nevertheless reappears in the fourth order away from the decoupling limit. We
also demonstrate that there is no direct relation between the value of the
Vainshtein scale and the existence of nonlinear ghost. We discuss how massive
gravity should be modified to avoid the appearance of the ghost.Comment: 16 page
The influence of D-branes' backreaction upon gravitational interactions between open strings
We argue that gravitational interactions between open strings ending on
D3-branes are largely shaped by the D3-branes' backreaction. To this end we
consider classical open strings coupled to general relativity in Poincare AdS5
backgrounds. We compute the linear gravitational backreaction of a static
string extending up to the Poincare horizon, and deduce the potential energy
between two such strings. If spacetime is non-compact, we find that the
gravitational potential energy between parallel open strings is independent of
the strings' inertial masses and goes like 1/r at large distance r. If the
space transverse to the D3-branes is suitably compactified, a collective mode
of the graviton propagates usual four-dimensional gravity. In that case the
backreaction of the D3-branes induces a correction to the Newtonian potential
energy that violates the equivalence principle. The observed enhancement of the
gravitational attraction is specific to string theory; there is no similar
effect for point-particles.Comment: 28 pages, 7 figures. Typos corrected, minor addition
Low-Energy Signals from Kinetic Mixing with a Warped Abelian Hidden Sector
We investigate the detailed phenomenology of a light Abelian hidden sector in
the Randall-Sundrum framework. Relative to other works with light hidden
sectors, the main new feature is a tower of hidden Kaluza-Klein vectors that
kinetically mix with the Standard Model photon and Z. We investigate the decay
properties of the hidden sector fields in some detail, and develop an approach
for calculating processes initiated on the ultraviolet brane of a warped space
with large injection momentum relative to the infrared scale. Using these
results, we determine the detailed bounds on the light warped hidden sector
from precision electroweak measurements and low-energy experiments. We find
viable regions of parameter space that lead to significant production rates for
several of the hidden Kaluza-Klein vectors in meson factories and fixed-target
experiments. This offers the possibility of exploring the structure of an extra
spacetime dimension with lower-energy probes.Comment: (1+32) Pages, 13 Figures. v2: JHEP version (minor modifications,
results unchanged
Direct Mediation and Metastable Supersymmetry Breaking for SO(10)
We examine a metastable Macroscopic SO(N) SQCD model of
Intriligator, Seiberg and Shih (ISS). We introduce various baryon and meson
deformations, including multitrace operators and explore embedding an SO(10)
parent of the standard model into two weakly gauged flavour sectors. Direct
fundamental messengers and the symmetric pseudo-modulus messenger mediate SUSY
breaking to the MSSM. Gaugino and sfermion masses are computed and compared for
each deformation type. We also explore reducing the rank of the magnetic quark
matrix of the ISS model and find an additional fundamental messenger.Comment: 43 pages, Latex. Version to appear in JHEP
Secluded Dark Matter Coupled to a Hidden CFT
Models of secluded dark matter offer a variant on the standard WIMP picture
and can modify our expectations for hidden sector phenomenology and detection.
In this work we extend a minimal model of secluded dark matter, comprised of a
U(1)'-charged dark matter candidate, to include a confining hidden-sector CFT.
This provides a technically natural explanation for the hierarchically small
mediator-scale, with hidden-sector confinement generating m_{gamma'}>0.
Furthermore, the thermal history of the universe can differ markedly from the
WIMP picture due to (i) new annihilation channels, (ii) a (potentially) large
number of hidden-sector degrees of freedom, and (iii) a hidden-sector phase
transition at temperatures T << M_{dm} after freeze out. The mediator allows
both the dark matter and the Standard Model to communicate with the CFT, thus
modifying the low-energy phenomenology and cosmic-ray signals from the secluded
sector.Comment: ~50p, 8 figs; v2 JHEP versio
On Horava-Lifshitz "Black Holes"
The most general spherically symmetric solution with zero shift is found in
the non-projectable Horava-Lifshitz class of theories with general coupling
constants. It contains as special cases, spherically symmetric solutions found
by other authors earlier. It is found that the generic solution has
conventional (AdS, dS or flat) asymptotics with a universal 1/r tail. There are
several special cases where the asymptotics differ, including the detailed
balance choice of couplings. The conventional thermodynamics of this general
class of solutions is established by calculating the energy, temperature and
entropy. Although several of the solutions have conventional horizons, for
particles with ultra-luminal dispersion relations such solutions appear to be
horizonless.Comment: Latex 41 pages, 5 figure
Effective Theory Approach to the Spontaneous Breakdown of Lorentz Invariance
We generalize the coset construction of Callan, Coleman, Wess and Zumino to
theories in which the Lorentz group is spontaneously broken down to one of its
subgroups. This allows us to write down the most general low-energy effective
Lagrangian in which Lorentz invariance is non-linearly realized, and to explore
the consequences of broken Lorentz symmetry without having to make any
assumptions about the mechanism that triggers the breaking. We carry out the
construction both in flat space, in which the Lorentz group is a global
spacetime symmetry, and in a generally covariant theory, in which the Lorentz
group can be treated as a local internal symmetry. As an illustration of this
formalism, we construct the most general effective field theory in which the
rotation group remains unbroken, and show that the latter is just the
Einstein-aether theory.Comment: 45 pages, no figures
Domain wall brane in squared curvature gravity
We suggest a thick braneworld model in the squared curvature gravity theory.
Despite the appearance of higher order derivatives, the localization of gravity
and various bulk matter fields is shown to be possible. The existence of the
normalizable gravitational zero mode indicates that our four-dimensional
gravity is reproduced. In order to localize the chiral fermions on the brane,
two types of coupling between the fermions and the brane forming scalar is
introduced. The first coupling leads us to a Schr\"odinger equation with a
volcano potential, and the other a P\"oschl-Teller potential. In both cases,
the zero mode exists only for the left-hand fermions. Several massive KK states
of the fermions can be trapped on the brane, either as resonant states or as
bound states.Comment: 18 pages, 5 figures and 1 table, references added, improved version
to be published in JHE
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