6,143 research outputs found
Old Inflation in String Theory
We propose a stringy version of the old inflation scenario which does not
require any slow-roll inflaton potential and is based on a specific example of
string compatification with warped metric. Our set-up admits the presence of
anti-D3-branes in the deep infrared region of the metric and a false vacuum
state with positive vacuum energy density. The latter is responsible for the
accelerated period of inflation. The false vacuum exists only if the number of
anti-D3-branes is smaller than a critical number and the graceful exit from
inflation is attained if a number of anti-D3-branes travels from the
ultraviolet towards the infrared region. The cosmological curvature
perturbation is generated through the curvaton mechanism.Comment: 31 pages, 3 figures; typos corrected and reference adde
All Maximal Independent Sets and Dynamic Dominance for Sparse Graphs
We describe algorithms, based on Avis and Fukuda's reverse search paradigm,
for listing all maximal independent sets in a sparse graph in polynomial time
and delay per output. For bounded degree graphs, our algorithms take constant
time per set generated; for minor-closed graph families, the time is O(n) per
set, and for more general sparse graph families we achieve subquadratic time
per set. We also describe new data structures for maintaining a dynamic vertex
set S in a sparse or minor-closed graph family, and querying the number of
vertices not dominated by S; for minor-closed graph families the time per
update is constant, while it is sublinear for any sparse graph family. We can
also maintain a dynamic vertex set in an arbitrary m-edge graph and test the
independence of the maintained set in time O(sqrt m) per update. We use the
domination data structures as part of our enumeration algorithms.Comment: 10 page
FRW cosmologies and hyperscaling-violating geometries: higher curvature corrections, ultrametricity, Q-space/QFT duality, and a little string theory
We analyze flat FRW cosmologies and hyperscaling-violating geometries by
emphasizing the analytic continuation between them and their scale covariance.
We exhibit two main calculations where this point of view is useful. First,
based on the scale covariance, we show that the structure of higher curvature
corrections to Einstein's equation is very simple. Second, in the context of
accelerated FRW cosmologies, also known as Q-space, we begin by calculating the
Bunch-Davies wavefunctional for a massless scalar field and considering its
interpretation as a generating functional of correlation functions of a
holographic dual. We use this to conjecture a Q-space/QFT duality, a natural
extension of dS/CFT, and argue that the Euclidean dual theory violates
hyperscaling. This proposal, when extended to epochs in our own cosmological
history like matter or radiation domination, suggests a holographically dual
description via RG phases which violate hyperscaling. We further use the
wavefunctional to compute Anninos-Denef overlaps and show that the ultrametric
structure discovered for de Sitter becomes sharper in accelerated FRW
cosmologies as the acceleration slows. The substitution permeates and illuminates the discussion of wavefunctionals
and overlaps in FRW cosmologies, allowing one to predict the sharpened
structure. We try to find an alternate manifestation of this ultrametric
structure by studying the connection of the background to
little string theory.Comment: 31 pages plus an appendix; v2 references added; v3 discussion of
generalized extreme value distributions added and typos correcte
Confinement of Brownian Polymers under Geometric Area Tilts
We consider tightness for families of non-colliding Brownian bridges above a
hard wall, which are subject to geometrically growing self-potentials of tilted
area type. The model is introduced in order to mimic level lines of
discrete Solid-On-Solid random interfaces above a hard wall.Comment: 22 pages, 3 figure
Gravitational Waves from Preheating in M-flation
Matrix inflation, or M-flation, is a string theory motivated inflationary
model with three scalar field matrices and gauge fields in the adjoint
representation of the gauge group. One of these scalars
appears as the effective inflaton while the rest of the fields (scalar and
gauge fields) can play the role of isocurvature fields during inflation and
preheat fields afterwards. There is a region in parameter space and initial
field values, "the hilltop region," where predictions of the model are quite
compatible with the recent Planck data. We show that in this hilltop region, if
the inflaton ends up in the supersymmetric vacuum, the model can have an
embedded preheating mechanism. Couplings of the preheat modes are related to
the inflaton self-couplings and therefore are known from the CMB data. Through
lattice simulations performed using a symplectic integrator, we numerically
compute the power spectra of gravitational waves produced during the preheating
stage following M-flation. The preliminary numerical simulation of the spectrum
from multi-preheat fields peaks in the GHz band with an amplitude
, suggesting that the model has
concrete predictions for the ultra-high frequency gravity-wave probes. This
signature could be used to distinguish the model from rival inflationary modelsComment: v1:27 pages and 7 figures; v2: typos corrected; v3: references added;
v4: matched the JCAP versio
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