21 research outputs found

### Massive Gravity on a Non-extremal Brane

We consider a brane world scenario which arises as the near-horizon region of
a non-extremal D5-brane. There is a quasi-localized massive graviton mode, as
well as harmonic modes of higher mass which are bound to the brane to a lesser
degree. Lorentz invariance is slightly broken, which may have observable
effects due to the leakage of the metastable graviton states into the bulk.
Unlike a brane world arising from an extremal D5-brane, there is no mass gap.
We also find that a brane world arising from a non-extremal M5/M5-brane
intersection has the same graviton dynamics as that of a non-extremal D5-brane.
This is evidence that a previously conjectured duality relation between the
dual quantum field theories of each p-brane background may hold away from
extremality.Comment: 10 pages, 4 figures, LaTe

### Smooth Cosmologies from M-theory

We review two ways in which smooth cosmological evolution between two de
Sitter phases can be obtained from M/string-theory. Firstly, we perform a
hyperbolic reduction of massive IIA* theory to D=6 N=(1,1) SU(2)xU(1) gauged de
Sitter supergravity, which supports smooth cosmological evolution between dS_4
x S^2 and a dS_6-type geometry. Secondly, we obtain four-dimensional de Sitter
gravity with SU(2) Yang-Mills gauge fields from a hyperbolic reduction of
standard eleven-dimensional supergravity. The four-dimensional theory supports
smooth cosmological evolution between dS_2 x S^2 and a dS_4-type geometry.
Although time-dependent, these solutions arise from a first-order system via a
superpotential construction. For appropriate choices of charges, these
solutions describe an expanding universe whose expansion rate is significantly
larger in the past than in the future, as required for an inflationary model.Comment: Latex, 7 pages, Contribution to Quantum Theory and Symmetries

### S^1-wrapped D3-branes on Conifolds

We construct a D3-brane wrapped on S^1, which is fibred over the resolved
conifold as its transverse space. Whereas a fractional D3-brane on the resolved
conifold is not supersymmetric and has a naked singularity, our solution is
supersymmetric and regular everywhere. We also consider an $S^1$-wrapped
D3-brane on the resolved cone over T^{1,1}/Z_2, as well as on the deformed
conifold. In the former case, we obtain a regular supergravity dual to a
certain four-dimensional field theory whose Lorentz and conformal symmetries
are broken in the IR region and restored in the UV limit.Comment: Latex, 14 pages, minor correction

### Non-singular Twisted S-branes From Rotating Branes

We show that rotating p-brane solutions admit an analytical continuation to
become twisted Sp-branes. Although a rotating p-brane has a naked singularity
for large angular momenta, the corresponding S-brane configuration is regular
everywhere and exhibits a smooth bounce between two phases of Minkowski
spacetime. If the foliating hyperbolic space of the transverse space is of even
dimension, such as for the twisted SM5-brane, then for an appropriate choice of
parameters the solution smoothly flows from a warped product of two-dimensional
de Sitter spacetime, five-dimensional Euclidean space and a hyperbolic 4-space
in the infinite past to Minkowski spacetime in the infinite future. We also
show that non-singular S-Kerr solutions can arise from higher-dimensional Kerr
black holes, so long as all (all but one) angular momenta are non-vanishing for
even (odd) dimensions.Comment: Latex, 20 page

### Branes and Brane Worlds in M-Theory

A new class of warped Anti-de Sitter solutions is found, arising as the
near-horizon region of various semi-localized brane intersections. The dual
gauge theories of AdS in warped spacetimes have reduced supersymmetry, which is
pertinent to the study of viable supersymmetric extensions of the Standard
Model. In addition, various supergravity solutions are probed via the
absorption of various fields. In particular, we calculate exact absorption
probabilities which provide finite-energy probes of supergravity solutions away
from the conformal limit. Lastly, we discuss how brane world scenarios may
arise from the near-horizon region of various p-brane configurations. Motivated
by the dual non-commutative gauge theory, it is shown how a background B field
mimics a negative four-dimensional cosmological constant, such that in both
cases there is a massive four-dimensional graviton.Comment: Ph.D. Thesis, Mirjam Cvetic (advisor), 189 pages, 15 figures, LaTe

### Absorption by Extremal D3-branes

The absorption in the extremal D3-brane background is studied for a class of
massless fields whose linear perturbations leave the ten-dimensional background
metric unperturbed, as well as the minimally-coupled massive scalar. We find
that various fields have the same absorption probability as that of the
dilaton-axion system, which is given exactly via the Mathieu equation. We
analyze the features of the absorption cross-sections in terms of effective
Schr\"odinger potentials, conjecture a general form of the dual effective
potentials, and provide explicit numerical results for the whole energy range.
As expected, all partial-wave absorption probabilities tend to zero (one) at
low (large) energies, and exhibit an oscillatory pattern as a function of
energy. The equivalence of absorption probabilities for various modes has
implications for the correlation functions on the field, including subleading
contributions on the field-theory side. In particular, certain half-integer and
integer spin fields have identical absorption probabilities, thus providing
evidence that the corresponding operator pairs on the field theory side belong
to the same supermultiplets.Comment: Latex, 9 figures and 17 page

### De Sitter Bounces

By analytically continuing recently-found instantons, we construct
time-dependent solutions of Einstein-Maxwell de Sitter gravity which smoothly
bounce between two de Sitter phases. These deformations of de Sitter space
undergo several stages in their time evolution. Four and five-dimensional de
Sitter bounces can be lifted to non-singular time-dependent solutions of
M-theory.Comment: Latex, 18 pages, 5 figure