579 research outputs found
Revisiting Cosmic No-Hair Theorem for Inflationary Settings
In this work we revisit Wald's cosmic no-hair theorem in the context of
accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing
anisotropic stress tensor and when the fluid energy momentum tensor is of the
form of a cosmological constant term plus a piece which does not respect strong
or dominant energy conditions. Such a fluid is the one appearing in
inflationary models. We show that for such a system anisotropy may grow, in
contrast to the cosmic no-hair conjecture. In particular, for a generic
inflationary model we show that there is an upper bound on the growth of
anisotropy. For slow-roll inflationary models our analysis can be refined
further and the upper bound is found to be of the order of slow-roll
parameters. We examine our general discussions and our extension of Wald's
theorem for three classes of slow-roll inflationary models, generic
multi-scalar field driven models, anisotropic models involving U(1) gauge
fields and the gauge-flation scenario.Comment: 21 pp, 4 .eps figure
An Arena for Model Building in the Cohen-Glashow Very Special Relativity
The Cohen-Glashow Very Special Relativity (VSR) algebra
[arXiv:hep-ph/0601236] is defined as the part of the Lorentz algebra which upon
addition of CP or T invariance enhances to the full Lorentz group, plus the
space-time translations. We show that noncommutative space-time, in particular
noncommutative Moyal plane, with light-like noncommutativity provides a robust
mathematical setting for quantum field theories which are VSR invariant and
hence set the stage for building VSR invariant particle physics models. In our
setting the VSR invariant theories are specified with a single deformation
parameter, the noncommutativity scale \Lambda_{NC}. Preliminary analysis with
the available data leads to \Lambda_{NC}\gtrsim 1-10 TeV.
This note is prepared for the Proceedings of the G27 Mathematical Physics
Conference, Yerevan 2008, and is based on arXiv:0806.3699[hep-th].Comment: Presented by M.M.Sh-J. in the G27 Mathematical Physics Conference,
Yerevan 2008 as the 4th Weyl Prize Ceremony Tal
Soft Charges and Electric-Magnetic Duality
The main focus of this work is to study magnetic soft charges of the four
dimensional Maxwell theory. Imposing appropriate asymptotic falloff conditions,
we compute the electric and magnetic soft charges and their algebra both at
spatial and at null infinity. While the commutator of two electric or two
magnetic soft charges vanish, the electric and magnetic soft charges satisfy a
complex current algebra. This current algebra through Sugawara
construction yields two Kac-Moody algebras. We repeat the charge
analysis in the electric-magnetic duality-symmetric Maxwell theory and
construct the duality-symmetric phase space where the electric and magnetic
soft charges generate the respective boundary gauge transformations. We show
that the generator of the electric-magnetic duality and the electric and
magnetic soft charges form infinite copies of algebra. Moreover, we
study the algebra of charges associated with the global Poincar\'e symmetry of
the background Minkowski spacetime and the soft charges. We discuss physical
meaning and implication of our charges and their algebra.Comment: 41 pages, 4 figures; published version in JHE
Shallow Water Memory: Stokes and Darwin Drifts
It has been shown in \cite{Tong:2022gpg} that shallow water in the Euler
description admits a dual gauge theory formulation. We show in the Lagrange
description this gauge symmetry is a manifestation of the 2 dimensional
area-preserving diffeomorphisms. We find surface charges associated with the
gauge symmetry and their algebra, and study their physics in the shallow water
system. In particular, we provide a reinterpretation of the Kelvin circulation
theorem in terms of conserved charges. In the linear shallow water case, the
charges form a u(1) current algebra with level proportional to the Coriolis
parameter over the height of the fluid. We also study memory effect for the
gauge theory description of the linearized shallow water and show Euler, Stokes
and Darwin drifts can be understood as a memory effect and/or change of the
surface charges in the gauge theory description.Comment: 28 pages, 2 figures, minor improvements, references adde
A note on bosonic open strings in constant B field
We sketch the main steps of old covariant quantization of bosonic open
strings in a constant field background. We comment on its space-time
symmetries and the induced effective metric. The low-energy spectrum is
evaluated and the appearance of a new non-commutative gauge symmetry is
addressed.Comment: 13 pages, Latex, important comments added, to appear in PR
Hydro & Thermo Dynamics at Causal Boundaries, Examples in 3d Gravity
We study 3-dimensional gravity on a spacetime bounded by a generic
2-dimensional causal surface. We review the solution phase space specified by 4
generic functions over the causal boundary, construct the symplectic form over
the solution space and the 4 boundary charges and their algebra. The boundary
charges label boundary degrees of freedom. Three of these charges extend and
generalize the Brown-York charges to the generic causal boundary, are canonical
conjugates of boundary metric components and naturally give rise to a fluid
description at the causal boundary. Moreover, we show that the boundary charges
besides the causal boundary hydrodynamic description, also admit a
thermodynamic description with a natural (geometric) causal boundary
temperature and angular velocity. When the causal boundary is the asymptotic
boundary of the 3d AdS or flat space, the hydrodynamic description respectively
recovers an extension of the known conformal or conformal-Carrollian asymptotic
hydrodynamics. When the causal boundary is a generic null surface, we recover
the null surface thermodynamics of [1] which is an extension of the usual black
hole thermodynamics description.Comment: 35 pages, 5 figure
Carrollian Structure of the Null Boundary Solution Space
We study pure dimensional Einstein gravity in spacetimes with a generic
null boundary. We focus on the symplectic form of the solution phase space
which comprises a dimensional boundary part and a
dimensional bulk part. The symplectic form is the sum of the bulk and boundary
parts, obtained through integration over a codimension 1 surface (null
boundary) and a codimension 2 spatial section of it, respectively. Notably,
while the total symplectic form is a closed 2-form over the solution phase
space, neither the boundary nor the bulk symplectic forms are closed due to the
symplectic flux of the bulk modes passing through the boundary. Furthermore, we
demonstrate that the dimensional Lagrangian submanifold of the
bulk part of the solution phase space has a Carrollian structure, with the
metric on the dimensional part being the Wheeler-DeWitt metric, and
the Carrollian kernel vector corresponding to the outgoing Robinson-Trautman
gravitational wave solution.Comment: 33 pages, 2 figures, references adde
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