255 research outputs found
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
4d Conformal Field Theories and Strings on Orbifolds
We propose correspondences between 4d quantum field theories with N=2,1,0
(super)conformal invariance and Type IIB string theory on various orbifolds. We
argue using the spacetime string theory, and check using the beta functions
(exactly for N=2,1 and so far at 1-loop for the gauge couplings in the N=0
case), that these theories have conformal fixed lines. The latter case
potentially gives well-defined non-supersymmetric vacua of string theory, with
a mechanism for making the curvature and cosmological constant small at
nontrivial string coupling. We suggest a correspondence between
nonsupersymmetric conformal fixed lines and nonsupersymmetric string vacua with
vanishing vacuum energy.Comment: 11 pages, harvmac big. Reference adde
ADS/CFT String Duality and Conformal Gauge Field Theories
Compactification of Type IIB superstring on an
background leads to SU(N) gauge field theories with prescribed matter
representations. In the 't Hooft limit of large N such theories are conformally
finite. For finite N and broken supersymmetry ( = 0) I derive the
constraints to be two-loop conformal and examine the consequences for a wide
choice of and its embedding .Comment: 10 pages LaTe
Towards a gauge invariant volume-weighted probability measure for eternal inflation
An improved volume-weighted probability measure for eternal inflation is
proposed. For the models studied in this paper it leads to simple and
intuitively expected gauge-invariant results.Comment: 16 pages, 3 figs, few misprints corrected, comments adde
Open string instantons and superpotentials
We study the F-terms in N=1 supersymmetric, d=4 gauge theories arising from
D(p+3)-branes wrapping supersymmetric p-cycles in a Calabi-Yau threefold. If p
is even the spectrum and superpotential for a single brane are determined by
purely classical () considerations. If p=3,
superpotentials for massless modes are forbidden to all orders in
and may only be generated by open string instantons. For this
latter case we find that such instanton effects are generically present. Mirror
symmetry relates even and odd p and thus perturbative and nonperturbative
superpotentials; we provide a preliminary discussion of a class of examples of
such mirror pairs.Comment: 22 pages, harvmac big; v2, corrected some typo
Multiple universes, cosmic coincidences, and other dark matters
Even when completely and consistently formulated, a fundamental theory of
physics and cosmological boundary conditions may not give unambiguous and
unique predictions for the universe we observe; indeed inflation, string/M
theory, and quantum cosmology all arguably suggest that we can observe only one
member of an ensemble with diverse properties. How, then, can such theories be
tested? It has been variously asserted that in a future measurement we should
observe the a priori most probable set of predicted properties (the
``bottom-up'' approach), or the most probable set compatible with all current
observations (the ``top-down'' approach), or the most probable set consistent
with the existence of observers (the ``anthropic'' approach). These inhabit a
spectrum of levels of conditionalization and can lead to qualitatively
different predictions. For example, in a context in which the densities of
various species of dark matter vary among members of an ensemble of otherwise
similar regions, from the top-down or anthropic viewpoints -- but not the
bottom-up -- it would be natural for us to observe multiple types of dark
matter with similar contributions to the observed dark matter density. In the
anthropic approach it is also possible in principle to strengthen this argument
and the limit the number of likely dark matter sub-components. In both cases
the argument may be extendible to dark energy or primordial density
perturbations. This implies that the anthropic approach to cosmology,
introduced in part to explain "coincidences" between unrelated constituents of
our universe, predicts that more, as-yet-unobserved coincidences should come to
light.Comment: 18 JCAP-style pages, accepted by JCAP. Revised version adds
references and some clarification
Building a Better Racetrack
We find IIb compactifications on Calabi-Yau orientifolds in which all Kahler
moduli are stabilized, along lines suggested by Kachru, Kallosh, Linde and
Trivedi.Comment: 47 pages, 1 figure, harvmac (v2: added references, minor comments,
v3: improved discussion of metastability and explicit flux vacua
A Review of Distributions on the String Landscape
We review some basic flux vacua counting techniques and results, focusing on
the distributions of properties over different regions of the landscape of
string vacua and assessing the phenomenological implications. The topics we
discuss include: an overview of how moduli are stabilized and how vacua are
counted; the applicability of effective field theory; the uses of and
differences between probabilistic and statistical analysis (and the relation to
the anthropic principle); the distribution of various parameters on the
landscape, including cosmological constant, gauge group rank, and SUSY-breaking
scale; "friendly landscapes"; open string moduli; the (in)finiteness of the
number of phenomenologically viable vacua; etc. At all points, we attempt to
connect this study to the phenomenology of vacua which are experimentally
viable.Comment: Invited review, IJMP A. LaTeX. 39 pages. References adde
Evidence for a bound on the lifetime of de Sitter space
Recent work has suggested a surprising new upper bound on the lifetime of de
Sitter vacua in string theory. The bound is parametrically longer than the
Hubble time but parametrically shorter than the recurrence time. We investigate
whether the bound is satisfied in a particular class of de Sitter solutions,
the KKLT vacua. Despite the freedom to make the supersymmetry breaking scale
exponentially small, which naively would lead to extremely stable vacua, we
find that the lifetime is always less than about exp(10^(22)) Hubble times, in
agreement with the proposed bound.Comment: 28 page
Orientifolds and Mirror Symmetry
We study parity symmetries and crosscap states in classes of N=2
supersymmetric quantum field theories in 1+1 dimensions, including non-linear
sigma models, gauged WZW models, Landau-Ginzburg models, and linear sigma
models. The parity anomaly and its cancellation play important roles in many of
them. The case of the N=2 minimal model are studied in complete detail, from
all three realizations -- gauged WZW model, abstract RCFT, and LG models. We
also identify mirror pairs of orientifolds, extending the correspondence
between symplectic geometry and algebraic geometry by including unorientable
worldsheets. Through the analysis in various models and comparison in the
overlapping regimes, we obtain a global picture of orientifolds and D-branes.Comment: 137 page
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