869 research outputs found
Dynamical solutions of warped six dimensional supergravity
We derive a new class of exact time dependent solutions in a warped six
dimensional supergravity model. Under the assumptions we make for the form of
the underlying moduli fields, we show that the only consistent time dependent
solutions lead to all six dimensions evolving in time, implying the eventual
decompactification or collapse of the extra dimensions. We also show how the
dynamics affects the quantization of the deficit angle.Comment: 18 pages, no figure, typos corrected, references added, the final
versio
Spacetime symmetries of the Lorentz-violating Maxwell-Chern-Simons model
The spacetime symmetries of classical electrodynamics supplemented with a
Chern-Simons term that contains a constant nondynamical 4-vector are
investigated. In addition to translation invariance and the expected three
remaining Lorentz symmetries characterized by the little group of the external
vector, the model possesses an additional spacetime symmetry if the
nondynamical vector is lightlike. The conserved current associated with this
invariance is determined, and the symmetry structure arising from this
invariance and the usual little group ISO(2) is identified as SIM(2).Comment: 5 pages, 1 table, REVTeX
Out of equilibrium: understanding cosmological evolution to lower-entropy states
Despite the importance of the Second Law of Thermodynamics, it is not
absolute. Statistical mechanics implies that, given sufficient time, systems
near equilibrium will spontaneously fluctuate into lower-entropy states,
locally reversing the thermodynamic arrow of time. We study the time
development of such fluctuations, especially the very large fluctuations
relevant to cosmology. Under fairly general assumptions, the most likely
history of a fluctuation out of equilibrium is simply the CPT conjugate of the
most likely way a system relaxes back to equilibrium. We use this idea to
elucidate the spacetime structure of various fluctuations in (stable and
metastable) de Sitter space and thermal anti-de Sitter space.Comment: 27 pages, 11 figure
Lorentz violation and the proper-time method
In this paper, we apply the proper-time method to generate the
Lorentz-violating Chern-Simons terms in the four-dimensional Yang-Mills and
non-linearized gravity theories. It is shown that the coefficient of the
induced Chern-Simons term is finite but regularization dependent.Comment: 11 pages, Revtex
Vortices, Infrared effects and Lorentz Invariance Violation
The Yang-Mills theory with noncommutative fields is constructed following
Hamiltonian and lagrangean methods. This modification of the standard
Yang-Mills theory shed light on the confinement mechanism viewed as a Lorentz
invariance violation (LIV) effect. The modified Yang-Mills theory contain in
addition to the standard contribution, the term where
is a given space-like constant vector with canonical dimension of
energy. The field rescaling and the choice ,
one can show that the modified Yang-Mills theory in 3+1 dimensions can be made
equivalent to a Yang-Mills-Chern-Simons theory in 2+1 dimensions if one
consider only heavy fermionic excitations. Thus, the Yang-Mills-Chern-Simons
theory in 2+1 dimensions is a codified way of that include only heavy
quarks. The classical solutions of the modified Yang-Mills theory for the SU(2)
gauge group are confining ones.Comment: Title changed and comments added. To appear in PL
Supersymmetric codimension-two branes in six-dimensional gauged supergravity
We consider the six-dimensional Salam-Sezgin supergravity in the presence of
codimension-2 branes. In the case that the branes carry only tension, we
provide a way to supersymmetrise them by adding appropriate localised
Fayet-Iliopoulos terms and localised corrections to the Chern-Simons term and
modifying accordingly the fermionic supersymmetry transformations. The
resulting brane action has N=1 supersymmetry (SUSY). We find the axisymmetric
vacua of the system and show that one has unwarped background solutions with
"football"-shaped extra dimensions which always respect N=1 SUSY for any value
of the equal brane tensions, in contrast with the non-supersymmetric brane
action background. Finally, we generically find multiple zero modes of the
gravitino in this background and discuss how one could obtain a single chiral
zero mode present in the low energy spectrum.Comment: 21 pages, no figures, A sign error in the gauge potential at the
lower brane corrected and its consequent effect discusse
Volume stabilization in a warped flux compactification model
We investigate the stability of the extra dimensions in a warped, codimension
two braneworld that is based upon an Einstein-Maxwell-dilaton theory with a
non-vanishing scalar field potential. The braneworld solution has two 3-branes,
which are located at the positions of the conical singularities. For this type
of brane solution the relative positions of the branes (the shape modulus) is
determined via the tension-deficit relations, if the brane tensions are fixed.
However, the volume of the extra dimensions (the volume modulus) is not fixed
in the context of the classical theory, implying we should take quantum
corrections into account. Hence, we discuss the one-loop effective potential of
the volume modulus for a massless, minimally coupled scalar field.Comment: 25 pages, 8 figures, typos correcte
Field theory models for variable cosmological constant
Anthropic solutions to the cosmological constant problem require seemingly
unnatural scalar field potentials with a very small slope or domain walls
(branes) with a very small coupling to a four-form field. Here we introduce a
class of models in which the smallness of the corresponding parameters can be
attributed to a spontaneously broken discrete symmetry. We also demonstrate the
equivalence of scalar field and four-form models. Finally, we show how our
models can be naturally embedded into a left-right extension of the standard
model.Comment: A reference adde
A no-go for no-go theorems prohibiting cosmic acceleration in extra dimensional models
A four-dimensional effective theory that arises as the low-energy limit of
some extra-dimensional model is constrained by the higher dimensional Einstein
equations. Steinhardt & Wesley use this to show that accelerated expansion in
our four large dimensions can only be transient in a large class of
Kaluza-Klein models that satisfy the (higher dimensional) null energy condition
[1]. We point out that these no-go theorems are based on a rather ad-hoc
assumption on the metric, without which no strong statements can be made.Comment: 20 page
Exact Black Holes and Gravitational Shockwaves on Codimension-2 Branes
We derive exact gravitational fields of a black hole and a relativistic
particle stuck on a codimension-2 brane in dimensions when gravity is ruled
by the bulk -dimensional Einstein-Hilbert action. The black hole is locally
the higher-dimensional Schwarzschild solution, which is threaded by a tensional
brane yielding a deficit angle and includes the first explicit example of a
`small' black hole on a tensional 3-brane. The shockwaves allow us to study the
large distance limits of gravity on codimension-2 branes. In an infinite
locally flat bulk, they extinguish as , i.e. as on a 3-brane
in , manifestly displaying the full dimensionality of spacetime. We check
that when we compactify the bulk, this special case correctly reduces to the 4D
Aichelburg-Sexl solution at large distances. Our examples show that gravity
does not really obstruct having general matter stress-energy on codimension-2
branes, although its mathematical description may be more involved.Comment: 18 pages, LaTeX; v2: added references, version to appear in JHE
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