22 research outputs found
Cosmological stabilization of moduli with steep potentials
A scenario which overcomes the well-known cosmological overshoot problem
associated with stabilizing moduli with steep potentials in string theory is
proposed. Our proposal relies on the fact that moduli potentials are very steep
and that generically their kinetic energy quickly becomes dominant. However,
moduli kinetic energy red-shifts faster than other sources when the universe
expands. So, if any additional sources are present, even in very small amounts,
they will inevitably become dominant. We show that in this case cosmic friction
allows the dissipation of the large amount of moduli kinetic energy that is
required for the field to be able to find an extremely shallow minimum. We
present the idea using analytic methods and verify with some numerical
examples.Comment: 15 pages, 5 figure
Inflationary cosmology in the central region of String/M-theory moduli space
The "central" region of moduli space of M- and string theories is where the
string coupling is about unity and the volume of compact dimensions is about
the string volume. Here we argue that in this region the non-perturbative
potential which is suggested by membrane instanton effects has the correct
scaling and shape to allow for enough slow-roll inflation, and to produce the
correct amplitude of CMB anisotropies. Thus, the well known theoretical
obstacles for achieving viable slow-roll inflation in the framework of
perturbative string theory are overcome. Limited knowledge of some generic
properties of the induced potential is sufficient to determine the simplest
type of consistent inflationary model and its predictions about the spectrum of
cosmic microwave background anisotropies: a red spectrum of scalar
perturbations, and negligible amount of tensor perturbations.Comment: 9 pages, 1 figur
Moduli potentials in string compactifications with fluxes: mapping the Discretuum
We find de Sitter and flat space solutions with all moduli stabilized in four
dimensional supergravity theories derived from the heterotic and type II string
theories, and explain how all the previously known obstacles to finding such
solutions can be removed. Further, we argue that if the compact manifold allows
a large enough space of discrete topological choices then it is possible to
tune the parameters of the four dimensional supergravity such that a hierarchy
is created and the solutions lie in the outer region of moduli space in which
the compact volume is large in string units, the string coupling is weak, and
string perturbation theory is valid. We show that at least two light chiral
superfields are required for this scenario to work, however, one field is
sufficient to obtain a minimum with an acceptably small and negative
cosmological constant. We discuss cosmological issues of the scenario and the
possible role of anthropic considerations in choosing the vacuum of the theory.
We conclude that the most likely stable vacuua are in or near the central
region of moduli space where string perturbation theory is not strictly valid,
and that anthropic considerations cannot help much in choosing a vacuum.Comment: 34 pages, no figure
Constraints on LVS Compactifications of IIB String Theory
We argue that once all theoretical and phenomenological constraints are
imposed on the different versions of the Large Volume Scenario (LVS)
compactifications of type IIB string theory, one particular version is favored.
This is essentially a sequestered one in which the soft terms are generated by
Weyl anomaly and RG running effects. We also show that arguments questioning
sequestering in LVS models are not relevant in this case.Comment: 14 pages, additional discussion of D7 brane case and mSUGRA,
reference adde
Moduli stabilization and supersymmetry breaking in effective theories of strings
The region of moduli space of string theories which is most likely to
describe the "real world" is where the string coupling is about unity and the
volume of extra compact dimensions is about the same size as the string volume.
Here we map the landscape of this "central" region in a model-independent way,
assuming only that the string coupling and compact volume moduli are chiral
superfields of N=1 supergravity in 4 dimensions, and requiring only widely
accepted conditions: that the supersymmetry (SUSY) breaking scale is about the
weak scale and that the cosmological constant be of acceptably small magnitude.
We find that the superpotential has (in the supersymmetric limit) a fourth
order zero in the SUSY breaking direction. The potential near the minimum is
very steep in the SUSY preserving directions, and very flat in the SUSY
breaking direction, consequently the SUSY breaking field has a weak scale mass,
while other moduli are heavy. We also argue that there will be additional near
by minima with a large negative cosmological constant.Comment: 12 pages, no figure
M-Theory Moduli Space and Cosmology
We conduct a systematic search for a viable string/M-theory cosmology,
focusing on cosmologies that include an era of slow-roll inflation, after which
the moduli are stabilized and the Universe is in a state with an acceptably
small cosmological constant. We observe that the duality relations between
different cosmological backgrounds of string/M-theory moduli space are greatly
simplified, and that this simplification leads to a truncated moduli space
within which possible cosmological solutions lie. We review some known
challenges to four dimensional models in the "outer", perturbative, region of
moduli space, and use duality relations to extend them to models of all of the
(compactified) perturbative string theories and 11D supergravity, including
brane world models. We conclude that cosmologies restricted to the outer region
are not viable, and that the most likely region of moduli space in which to
find realistic cosmology is the "central", non-perturbative region, with
coupling and compact volume both of order unity, in string units.Comment: 42 pages, 3 figure
Maximal Temperature in Flux Compactifications
Thermal corrections have an important effect on moduli stabilization leading
to the existence of a maximal temperature, beyond which the compact dimensions
decompactify. In this note, we discuss generality of our earlier analysis and
apply it to the case of flux compactifications. The maximal temperature is
again found to be controlled by the supersymmetry breaking scale, T_{crit} \sim
\sqrt{m_{3/2} M_P}.Comment: 10 pages, 10 figures. v2:comment and references adde
String Universality
If there is a single underlying "theory of everything" which in some limits
of its "moduli space" reduces to the five weakly coupled string theories in
10D, and 11D SUGRA, then it is possible that all six of them have some common
domain of validity and that they are in the same universality class, in the
sense that the 4D low energy physics of the different theories is the same. We
call this notion String Universality. This suggests that the true vacuum of
string theory is in a region of moduli space equally far (in some sense) from
all perturbative theories, most likely around the self-dual point with respect
to duality symmetries connecting them. We estimate stringy non-perturbative
effects from wrapped brane instantons in each perturbative theory, show how
they are related by dualities, and argue that they are likely to lead to moduli
stabilization only around the self-dual point. We argue that moduli
stabilization should occur near the string scale, and SUSY breaking should
occur at a much lower intermediate scale, and that it originates from different
sources. We discuss the problems of moduli stabilization and SUSY breaking in
currently popular scenarios, explain why these problems are generic, and
discuss how our scenario can evade them. We show that String Universality is
not inconsistent with phenomenology but that it is in conflict with some
popular versions of brane world scenarios.Comment: 48 pages, 1 figure; one reference adde
Inflation as a probe of new physics
In this paper we consider inflation as a probe of new physics near the string
or Planck scale. We discuss how new physics can be captured by the choice of
vacuum, and how this leads to modifications of the primordial spectrum as well
as the way in which the universe expands during inflation. Provided there is a
large number of fields contributing to the vacuum energy -- as typically is
expected in string theory -- we will argue that both types of effects can be
present simultaneously and be of observational relevance. Our conclusion is
that the ambiguity in choice of vacuum is an interesting new parameter in
serious model building.Comment: 14 page