1,941 research outputs found
Flux Compactification
We review recent work in which compactifications of string and M theory are
constructed in which all scalar fields (moduli) are massive, and supersymmetry
is broken with a small positive cosmological constant, features needed to
reproduce real world physics. We explain how this work implies that there is a
``landscape'' of string/M theory vacua, perhaps containing many candidates for
describing real world physics, and present the arguments for and against this
idea. We discuss statistical surveys of the landscape, and the prospects for
testable consequences of this picture, such as observable effects of moduli,
constraints on early cosmology, and predictions for the scale of supersymmetry
breaking.Comment: 66 pages, 3 figures, Latex with revtex4 macros. v3: version to appear
in RM
Physics of String Flux Compactifications
We provide a qualitative review of flux compactifications of string theory,
focusing on broad physical implications and statistical methods of analysis.Comment: 39 pages, Latex ar2e.cl
Gravitational backreaction of anti-D branes in the warped compactification
We derive a low-energy effective theory for gravity with anti-D branes, which
are essential to get de Sitter solutions in the type IIB string warped
compactification, by taking account of gravitational backreactions of anti-D
branes. In order to see the effects of the self-gravity of anti-D branes, a
simplified model is studied where a 5-dimensional anti-de Sitter ({\it AdS})
spacetime is realized by the bulk cosmological constant and the 5-form flux,
and anti-D branes are coupled to the 5-form field by Chern-Simon terms. The
{\it AdS} spacetime is truncated by introducing UV and IR cut-off branes like
the Randall-Sundrum model. We derive an effective theory for gravity on the UV
brane and reproduce the familiar result that the tensions of the anti-D branes
give potentials suppressed by the forth-power of the warp factor at the
location of the anti-D branes. However, in this simplified model, the potential
energy never inflates the UV brane, although the anti-D-branes are inflating.
The UV brane is dominated by dark radiation coming from the projection of the
5-dimensional Weyl tensor, unless the moduli fields for the anti-D branes are
stabilized. We comment on the possibility of avoiding this problem in a
realistic string theory compactification.Comment: typos corrected, 11 pages, 3 figure
The Scaling of the No Scale Potential and de Sitter Model Building
We propose a variant of the KKLT (A)dS flux vacuum construction which does
not require an antibrane to source the volume modulus. The strategy is to find
nonzero local minima of the no-scale potential in the complex structure and
dilaton directions in moduli space. The corresponding no-scale potential
expanded about this point sources the volume modulus in the same way as does
the antibrane of the KKLT construction. We exhibit explicit examples of such
nonzero local minima of the no-scale potential in a simple toroidal orientifold
model.Comment: 11 pages, harvmac big. v2: trivial typos fixe
Compactification Effects in D-brane Inflation
We determine the scalar potential for a D3-brane in a warped conifold
background subject to general ultraviolet perturbations. Incorporating the
effects of imaginary anti-self-dual (IASD) fluxes and four-dimensional
curvature at the nonlinear level, we compute the leading terms in the D3-brane
potential. We then provide strong cross-checks of our results by reproducing
them in the dual gauge theory. Finally, we observe that the D3-brane potential
induced by nonperturbative effects on D7-branes can be represented by a
ten-dimensional supergravity solution containing suitable IASD fluxes. Our
method allows for the systematic inclusion of compactification effects and
serves to constrain the D3-brane effective action in a large class of
stabilized compactifications.Comment: 4 pages; v2: minor correction
Aspects of brane-antibrane inflation
I describe a dynamical mechanism for solving the fine-tuning problem of
brane-antibrane inflation. By inflating with stacks of branes and antibranes,
the branes can naturally be trapped at a metastable minimum of the potential.
As branes tunnel out of this minimum, the shape of the potential changes to
make the minimum shallower. Eventually the minimum disappears and the remaining
branes roll slowly because the potential is nearly flat. I show that even with
a small number of branes, there is a good chance of getting enough inflation.
Running of the spectral index is correlated with the tilt in such a way as to
provide a test of the model by future CMB experiments.Comment: 6 pages, 5 figures; proceedings of Theory Canada 1 conference, 2-5
June 2005, UBC, Vancouve
On the Taxonomy of Flux Vacua
We investigate several predictions about the properties of IIB flux vacua on
Calabi-Yau orientifolds, by constructing and characterizing a very large set of
vacua in a specific example, an orientifold of the Calabi-Yau hypersurface in
. We find support for the prediction of Ashok and Douglas
that the density of vacua on moduli space is governed by where and are curvature and K\"ahler forms on the moduli
space. The conifold point on moduli space therefore serves as an
attractor, with a significant fraction of the flux vacua contained in a small
neighborhood surrounding . We also study the functional dependence of
the number of flux vacua on the D3 charge in the fluxes, finding simple power
law growth.Comment: 22 pages, harvmac; v2 typos corrected, refs added; v3 minor error
correcte
Rapid Tunneling and Percolation in the Landscape
Motivated by the possibility of a string landscape, we reexamine tunneling of
a scalar field across single/multiple barriers. Recent investigations have
suggested modifications to the usual picture of false vacuum decay that lead to
efficient and rapid tunneling in the landscape when certain conditions are met.
This can be due to stringy effects (e.g. tunneling via the DBI action), or by
effects arising due to the presence of multiple vacua (e.g. resonance
tunneling). In this paper we discuss both DBI tunneling and resonance
tunneling. We provide a QFT treatment of resonance tunneling using the
Schr\"odinger functional approach. We also show how DBI tunneling for
supercritical barriers can naturally lead to conditions suitable for resonance
tunneling. We argue using basic ideas from percolation theory that tunneling
can be rapid in a landscape where a typical vacuum has multiple decay channels
and discuss various cosmological implications. This rapidity vacuum decay can
happen even if there are no resonance/DBI tunneling enhancements, solely due to
the presence of a large number of decay channels. Finally, we consider various
ways of circumventing a recent no-go theorem for resonance tunneling in quantum
field theory.Comment: 47 pages, 16 figures. Acknowledgements adde
Multi-Throat Brane Inflation
We present a scenario where brane inflation arises more generically. We start
with D3 and anti-D3-branes at the infrared ends of two different throats. This
setup is a natural consequence of the assumption that in the beginning we have
a multi-throat string compactification with many wandering anti-D3-branes. A
long period of inflation is triggered when D3-branes slowly exit the highly
warped infrared region, under a potential generically arising from the moduli
stabilization. In this scenario, the usual slow-roll conditions are not
required, and a large warping is allowed to incorporate the Randall-Sundrum
model.Comment: 11 pages; v3: minor revision, PRD versio
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