72 research outputs found
Scalar field inflation driven by a modification of the Heisenberg algebra
We study the modifications induced on scalar field inflation produced by
considering a general modification of the Heisenberg algebra. We proceed by
modifying the Poisson brackets on the classical theory whenever the
corresponding quantum commutator is modified. We do not restrict ourselves to a
specific form for such modification, instead we constrain the functions
involved by the cosmological behaviour of interest. We present whenever
possible the way in which inflation can be realized approximately via three
slow roll Hubble parameters that depend on the standard slow roll parameters in
a very different form than in the usual case and that can be less restrictive.
Furthermore we find a general analytical solution describing an expanding
universe with constant Hubble parameter that generalizes the standard
cosmological constant case by restricting the form of the modification of the
Heisenberg algebra. It is found that even if such modification can be neglected
in some limit and the cosmological constant is set to zero in that limit, the
exponential expansion is present when the modification is important. Thus an
appropriate modification of the Heisenberg algebra is sufficient to produce an
exponentially expanding universe without the need of any other source.Comment: 34 pages, 1 figur
Lorentzian Vacuum Transitions in Ho\v{r}ava-Lifshitz Gravity
The vacuum transition probabilities for a
Friedmann-Lema\^itre-Robertson-Walker universe with positive curvature in
Ho\v{r}ava-Lifshitz gravity in the presence of a scalar field potential in the
Wentzel-Kramers-Brillouin approximation are studied. We use a general procedure
to compute such transition probabilities using a Hamiltonian approach to the
Wheeler-DeWitt equation presented in a previous work. We consider two
situations of scalar fields, one in which the scalar field depends on all the
spacetime variables and other in which the scalar field depends only on the
time variable. In both cases analytic expressions for the vacuum transition
probabilities are obtained and the infrared and ultraviolet limits are
discussed for comparison with the result obtained by using general relativity.
For the case in which the scalar field depends on all spacetime variables we
obtain that in the infrared limit it is possible to obtain a similar behavior
as in general relativity, however in the ultraviolet limit the behavior found
is completely opposite. Some few comments about possible phenomenological
implications of our results are given. One of them is a plausible resolution of
the initial singularity. On the other hand for the case in which the scalar
field depends only on the time variable, the behavior coincides with that of
general relativity in both limits, although in the intermediate region the
probability is slightly altered.Comment: 26 pages, 2 figures. Some references adde
The dispersive self-dual Einstein equations and the Toda lattice
The Boyer-Finley equation, or -Toda equation is both a reduction
of the self-dual Einstein equations and the dispersionlesslimit of the
-Toda lattice equation. This suggests that there should be a dispersive
version of the self-dual Einstein equation which both contains the Toda lattice
equation and whose dispersionless limit is the familiar self-dual Einstein
equation. Such a system is studied in this paper. The results are achieved by
using a deformation, based on an associative -product, of the algebra
used in the study of the undeformed, or dispersionless,
equations.Comment: 11 pages, LaTeX. To appear: J. Phys.
p-Branes from Generalized Yang-Mills Theory
We consider the reduced, quenched version of a generalized Yang-Mills action
in 4k-dimensional spacetime. This is a new kind of matrix theory which is
mapped through the Weyl-Wigner-Moyal correspondence into a field theory over a
non-commutative phase space. We show that the ``classical'' limit of this field
theory is encoded into the effective action of an open, (4k-1)-dimensional,
bulk brane enclosed by a dynamical, Chern-Simons type, (4k-2)-dimensional,
boundary brane. The bulk action is a pure volume term, while the boundary
action carries all the dynamical degrees of freedom.Comment: 8 pages, LaTeX 2e, no figure
Iso-spectral potential and inflationary quantum cosmology
Using the factorization approach of quantum mechanics, we obtain a family of
isospectral scalar potentials for power law inflationary cosmology. The
construction is based on a scattering Wheeler-DeWitt solution. These
iso-spectrals have new features, they give a mechanism to end inflation, as
well as the possibility to have new inflationary epochs. The procedure can be
extended to other cosmological models.Comment: 14 pages, 5 figure
(De)constructing Intersecting M5-branes
We describe intersecting M5-branes, as well as M5-branes wrapping the
holomorphic curve xy=c, in terms of a limit of a defect conformal field theory
with two-dimensional (4,0) supersymmetry. This dCFT describes the low-energy
theory of intersecting D3-branes at a C^2/Z_k orbifold. In an appropriate k ->
infinity limit, two compact spatial directions are generated. By identifying
moduli of the M5-M5 intersection in terms of those of the dCFT, we argue that
the SU(2)_L R-symmetry of the (4,0) defect CFT matches the SU(2) R-symmetry of
the N =2, d=4 theory of the M5-M5 intersection. We find a 't Hooft anomaly in
the SU(2)_L R-symmetry, suggesting that tensionless strings give rise to an
anomaly in the SU(2) R-symmetry of intersecting M5-branes.Comment: latex, 25 pages, 4 figure
Worldvolume Uncertainty Relations for D-Branes
By quantizing an open string ending on a D-brane in a nontrivial supergravity
background, we argue that there is a new kind of uncertainty relation on a
D-brane worldvolume. Furthermore, we fix the form of the uncertainty relations
and their dependence on the string coupling constant by requiring them to be
consistent with various string theory and M theory dualities. In this way we
find a web of uncertainties of spacetime for all kinds of brane probes,
including fundamental strings, D-branes of all dimensions as well as M theory
membranes and fivebranes.Comment: 19 pages, minor modification on p.
Dirichlet Branes on Orientifolds
We consider the classification of BPS and non-BPS D-branes in orientifold
models. In particular we construct all stable BPS and non-BPS D-branes in the
Gimon-Polchinski (GP) and Dabholkar-Park-Blum-Zaffaroni (DPBZ) orientifolds and
determine their stability regions in moduli space as well as decay products. We
find several kinds of integrally and torsion charged non-BPS D-branes. Certain
of these are found to have projective representations of the orientifold
GSO group on the Chan-Paton factors. It is found that the GP
orientifold is not described by equivariant orthogonal K-theory as may have
been at first expected. Instead a twisted version of this K-theory is expected
to be relevant.Comment: 33 pages, LaTeX, 5 figures. v2 typos corrected, references included,
(4,s)-branes re-examine
Noncommutative cosmological models coupled to a perfect fluid and a cosmological constant
In this work we carry out a noncommutative analysis of several
Friedmann-Robert-Walker models, coupled to different types of perfect fluids
and in the presence of a cosmological constant. The classical field equations
are modified, by the introduction of a shift operator, in order to introduce
noncommutativity in these models. We notice that the noncommutative versions of
these models show several relevant differences with respect to the
correspondent commutative ones.Comment: 27 pages. 7 figures. JHEP style.arXiv admin note: substantial text
overlap with arXiv:1104.481
Noncommutative geometry and physics: a review of selected recent results
This review is based on two lectures given at the 2000 TMR school in Torino.
We discuss two main themes: i) Moyal-type deformations of gauge theories, as
emerging from M-theory and open string theories, and ii) the noncommutative
geometry of finite groups, with the explicit example of Z_2, and its
application to Kaluza-Klein gauge theories on discrete internal spaces.Comment: Based on lectures given at the TMR School on contemporary string
theory and brane physics, Jan 26- Feb 2, 2000, Torino, Italy. To be published
in Class. Quant. Grav. 17 (2000). 3 ref.s added, typos corrected, formula on
exterior product of n left-invariant one-forms corrected, small changes in
the Sect. on integratio
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