52 research outputs found
Natural inflation and moduli stabilization in heterotic orbifolds
We study moduli stabilization in combination with inflation in heterotic
orbifold compactifications in the light of a large Hubble scale and the favored
tensor-to-scalar ratio . To account for a trans-Planckian field
range we implement aligned natural inflation. Although there is only one
universal axion in heterotic constructions, further axions from the geometric
moduli can be used for alignment and inflation. We argue that such an alignment
is rather generic on orbifolds, since all non-perturbative terms are determined
by modular weights of the involved fields and the Dedekind function. We
present two setups inspired by the mini-landscape models of the orbifold which realize aligned inflation and stabilization of
the relevant moduli. One has a supersymmetric vacuum after inflation, while the
other includes a gaugino condensate which breaks supersymmetry at a high scale.Comment: 17 pages, 5 tables, comments and references adde
Inflation with Fayet-Iliopoulos Terms
Two of the most attractive realizations of inflation in supergravity are
based upon the presence of a constant Fayet-Iliopoulos (FI) term. In D-term
hybrid inflation it is the FI term itself which sets the energy scale of
inflation. Alternatively, the breaking of a U(1) symmetry induced by the FI
term can dynamically generate the quadratic potential of chaotic inflation. The
purpose of this note is to study the possible UV embedding of these schemes in
terms of the `field-dependent FI term' related to a string modulus field which
is stabilized by a non-perturbative superpotential. We find that in settings
where the FI term drives inflation, gauge invariance prevents a decoupling of
the modulus from the inflationary dynamics. The resulting inflation models
generically contain additional dynamical degrees of freedom compared to D-term
hybrid inflation. However, the dynamical realization of chaotic inflation can
be obtained in complete analogy to the case of a constant FI term. We present a
simple string-inspired toy model of this type.Comment: 20 pages, accepted for publication in PR
Challenges for D-brane large-field inflation with stabilizer fields
We study possible string theory compactifications which, in the low-energy
limit, describe chaotic inflation with a stabilizer field. We first analyze
type IIA setups where the inflationary potential arises from a D6-brane
wrapping an internal three-cycle, and where the stabilizer field is either an
open-string or bulk K\"ahler modulus. We find that after integrating out the
relevant closed-string moduli consistently, tachyonic directions arise during
inflation which cannot be lifted. This is ultimately due to the shift
symmetries of the type IIA K\"ahler potential at large compactification volume.
This motivates us to search for stabilizer candidates in the complex structure
sector of type IIB orientifolds, since these fields couple to D7-brane Wilson
lines and their shift symmetries are generically broken away from the large
complex structure limit. However, we find that in these setups the challenge is
to obtain the necessary hierarchy between the inflationary and Kaluza-Klein
scales.Comment: 26 pages, typos corrected and comments added. Published versio
Supersymmetric Moduli Stabilization and High-Scale Inflation
We study the back-reaction of moduli fields on the inflaton potential in
generic models of F-term inflation. We derive the moduli corrections as a power
series in the ratio of Hubble scale and modulus mass. The general result is
illustrated with two examples, hybrid inflation and chaotic inflation. We find
that in both cases the decoupling of moduli dynamics and inflation requires
moduli masses close to the scale of grand unification. For smaller moduli
masses the CMB observables are strongly affected.Comment: 5 page
UV Corrections in Sgoldstino-less Inflation
We study the embedding of inflation with nilpotent multiplets in
supergravity, in particular the decoupling of the sgoldstino scalar field.
Instead of being imposed by hand, the nilpotency constraint on the goldstino
multiplet arises in the low energy-effective theory by integrating out heavy
degrees of freedom. We present explicit supergravity models in which a large
but finite sgoldstino mass arises from Yukawa or gauge interactions. In both
cases the inflaton potential receives two types of corrections. One is from the
backreaction of the sgoldstino, the other from the heavy fields generating its
mass. We show that these scale oppositely with the Volkov-Akulov cut-off scale,
which makes a consistent decoupling of the sgoldstino nontrivial. Still, we
identify a parameter window in which sgoldstino-less inflation can take place,
up to corrections which flatten the inflaton potential.Comment: 7 pages, 1 figure. Comments added, published versio
Higgs-otic Inflation and Moduli Stabilization
We study closed-string moduli stabilization in Higgs-otic inflation in Type
IIB orientifold backgrounds with fluxes. In this setup large-field inflation is
driven by the vacuum energy of mobile D7-branes. Imaginary selfdual (ISD)
three-form fluxes in the background source a -term and the necessary
monodromy for large field excursions while imaginary anti-selfdual (IASD)
three-form fluxes are sourced by non-perturbative contributions to the
superpotential necessary for moduli stabilization. We analyze K\"ahler moduli
stabilization and backreaction on the inflaton potential in detail. Confirming
results in the recent literature, we find that integrating out heavy K\"ahler
moduli leads to a controlled flattening of the inflaton potential. We quantify
the flux tuning necessary for stability even during large-field inflation.
Moreover, we study the backreaction of supersymmetrically stabilized complex
structure moduli and the axio-dilaton in the K\"ahler metric of the inflaton.
Contrary to previous findings, this backreaction can be pushed far out in field
space if a similar flux tuning as in the K\"ahler sector is possible. This
allows for a trans-Planckian field range large enough to support inflation.Comment: 42 pages, 10 figures, v2: comments and references added. Published
versio
The DBI Action, Higher-derivative Supergravity, and Flattening Inflaton Potentials
In string theory compactifications it is common to find an effective
Lagrangian for the scalar fields with a non-canonical kinetic term. We study
the effective action of the scalar position moduli of Type II D-branes. In
many instances the kinetic terms are in fact modified by a term proportional to
the scalar potential itself. This can be linked to the appearance of
higher-dimensional supersymmetric operators correcting the K\"ahler potential.
We identify the supersymmetric dimension-eight operators describing the
corrections captured by the D-brane Dirac-Born-Infeld action. Our
analysis then allows an embedding of the D-brane moduli effective action into
an supergravity formulation. The effects of the
potential-dependent kinetic terms may be very important if one of the scalars
is the inflaton, since they lead to a flattening of the scalar potential. We
analyze this flattening effect in detail and compute its impact on the CMB
observables for single-field inflation with monomial potentials.Comment: 25 pages, 3 figures. Comments and references added. Published versio
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