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59
Things fall apart: Topology change from winding tachyons,” arXiv:hepth/0502021
"... We argue that closed string tachyons drive two spacetime topology changing transitions – loss of genus in a Riemann surface and separation of a Riemann surface into two components. The tachyons of interest are localized versions of ScherkSchwarz winding string tachyons arising on Riemann surfaces i ..."
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Cited by 56 (6 self)
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We argue that closed string tachyons drive two spacetime topology changing transitions – loss of genus in a Riemann surface and separation of a Riemann surface into two components. The tachyons of interest are localized versions of ScherkSchwarz winding string tachyons arising on Riemann surfaces in regions of moduli space where stringscale tubes develop. Spacetime and worldsheet renormalization group analyses provide strong evidence that the decay of these tachyons removes a portion of the spacetime, splitting the tube into two pieces. We address the fate of the gauge fields and charges lost in the process, generalize it to situations with weak flux backgrounds, and use this process to study the type 0 tachyon, providing further evidence that its decay drives the theory subcritical. Finally, we discuss the timedependent dynamics of this topologychanging transition and find that it can occur more efficiently than analogous transitions on extended supersymmetric moduli spaces, which are limited by moduli trapping. January
The tachyon at the end of the universe
 JHEP
"... We show that a tachyon condensate phase replaces the spacelike singularity in certain cosmological and black hole spacetimes in string theory. We analyze explicitly a set of examples with flat spatial slices in various dimensions which have a winding tachyon condensate, using worldsheet path integra ..."
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Cited by 38 (6 self)
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We show that a tachyon condensate phase replaces the spacelike singularity in certain cosmological and black hole spacetimes in string theory. We analyze explicitly a set of examples with flat spatial slices in various dimensions which have a winding tachyon condensate, using worldsheet path integral methods from Liouville theory. In a vacuum with no excitations above the tachyon background in the wouldbe singular region, we analyze the production of closed strings in the resulting state in the bulk of spacetime. We find a thermal result reminiscent of the HartleHawking state, with tunably small energy density. The amplitudes exhibit a selfconsistent truncation of support to the weaklycoupled smalltachyon region of spacetime. We argue that the background is accordingly robust against back reaction, and that the resulting string theory amplitudes are perturbatively finite, indicating a resolution of the singularity and a mechanism to start or end time in string theory. Finally, we discuss the generalization of these methods to examples with positively curved spatial slices. July
Proton decay, Yukawa couplings and underlying gauge symmetry in string theory, Nucl.Phys. B747
, 2006
"... In string theory, massless particles often originate from a symmetry breaking of a large gauge symmetry G to its subgroup H. The absence of dimension4 proton decay in supersymmetric theories suggests that ( ¯ D,L) are different from ¯ H(¯5) in their origins. In this article, we consider a possibil ..."
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Cited by 37 (14 self)
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In string theory, massless particles often originate from a symmetry breaking of a large gauge symmetry G to its subgroup H. The absence of dimension4 proton decay in supersymmetric theories suggests that ( ¯ D,L) are different from ¯ H(¯5) in their origins. In this article, we consider a possibility that they come from different irreducible components in g/h. Requiring that all the Yukawa coupling constants of quarks and leptons be generated from the super Yang–Mills interactions of G, we found in the context of Georgi–Glashow H =SU(5) unification that the minimal choice of G is E7 and E8 is the only alternative. This idea is systematically implemented in Heterotic String, M theory and F theory, confirming the absence of dimension 4 proton decay operators. Not only H = SU(5) but also G constrain operators of effective field theories, String theory is a wellformulated theory of quantum gravity, and it is also known to be able to (almost) realize the (supersymmetric) standard model of particle physics at lowenergies [1, 2, 3, 4, 5, 6]. Since 1990’s, the understanding of string theory has improved dramatically,
On the explicit construction and statistics of CalabiYau flux vacua,” hepth/0409215
"... We explicitly construct and study the statistics of flux vacua for type IIB string theory on an orientifold of the CalabiYau hypersurface P 4 [1,1,2,2,6], parametrised by two relevant complex structure moduli. We solve for these moduli and the dilaton field in terms of the set of integers defining ..."
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Cited by 29 (2 self)
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We explicitly construct and study the statistics of flux vacua for type IIB string theory on an orientifold of the CalabiYau hypersurface P 4 [1,1,2,2,6], parametrised by two relevant complex structure moduli. We solve for these moduli and the dilaton field in terms of the set of integers defining the 3form fluxes and examine the distribution of vacua. We compare our numerical results with the predictions of the AshokDouglas density det(−R −ω), finding good overall agreement in different regions of moduli space. The number of vacua are found to scale with the distance in flux space. Vacua cluster in the region close to the conifold singularity. Large supersymmetry breaking is more generic but supersymmetric and hierarchical supersymmetry breaking vacua can also be obtained. In particular, the small superpotentials and large dilaton VEVs needed to obtain de Sitter space in a controllable approximation are possible but not generic. We argue that in a general flux compactification, the rank of the gauge group
Monodromy in the CMB: Gravity waves and string inflation,” arXiv:0803.3085 [hepth]; – 71
 J. High Energy Phys
"... We present a simple mechanism for obtaining largefield inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to φ 2/3 in terms of the canonically normalized field φ, yielding p ..."
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Cited by 20 (1 self)
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We present a simple mechanism for obtaining largefield inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to φ 2/3 in terms of the canonically normalized field φ, yielding predictions for the tilt of the power spectrum and the tensortoscalar ratio, ns ≈ 0.98 and r ≈ 0.04 with 60 efoldings of inflation; we note also the possibility of a variant with a candidate inflaton potential proportional to φ 2/5. The basic mechanism involved in extending the field range – monodromy in Dbranes as they move in circles on the manifold – arises in a more general class of compactifications, though our methods for controlling the
LMUASC02/08 Inflation at the Tip
, 802
"... We study the motion of a (space filling) D3brane at the tip of a warped deformed conifold, looking for inflationary trajectories. In our setup no anti D3brane is present and the inflaton potential is induced by threshold corrections to the superpotential. First we study the slow roll regime and fi ..."
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Cited by 15 (3 self)
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We study the motion of a (space filling) D3brane at the tip of a warped deformed conifold, looking for inflationary trajectories. In our setup no anti D3brane is present and the inflaton potential is induced by threshold corrections to the superpotential. First we study the slow roll regime and find that, allowing for fine tuning, hilltop inflation compatible with CMB data can take place. Then we consider the DBI regime and formulate a necessary condition for a phenomenologically viable inflationary stage. En passant, we propose a mechanism to cancel the large inflaton mass in the standard radial D3anti D3brane inflation. 1
Relativistic DBrane Scattering is Extremely Inelastic
"... We study the effects of quantum production of open strings on the relativistic scattering of Dbranes. We find strong corrections to the brane trajectory from copious production of highlyexcited open strings, whose typical oscillator level is proportional to the square of the rapidity. In the corre ..."
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Cited by 15 (1 self)
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We study the effects of quantum production of open strings on the relativistic scattering of Dbranes. We find strong corrections to the brane trajectory from copious production of highlyexcited open strings, whose typical oscillator level is proportional to the square of the rapidity. In the corrected trajectory, the branes rapidly coincide and remain trapped in a configuration with enhanced symmetry. This is a purely stringy effect which makes relativistic brane collisions exceptionally inelastic. We observe that paircreation of open strings could play an important role in cosmological scenarios in which branes approach each other at very high speeds. Thought experiments involving the scattering of strings or of Dbranes provide the key to understanding certain essential phenomena in string theory. The discovery of strings in the theory is perhaps the most striking case, but other examples include the elucidation of the sizes of strings under various conditions and the appreciation of
The dS/dS correspondence
 AIP Conf. Proc. 743, 393
, 2005
"... We present a holographic duality for the de Sitter static patch which consolidates basic features of its geometry and the behavior of gravity and brane probes, valid on timescales short compared to the decay or Poincare recurrence times. Namely de Sitter spacetime dSd(R) in d dimensions with curvatu ..."
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Cited by 14 (4 self)
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We present a holographic duality for the de Sitter static patch which consolidates basic features of its geometry and the behavior of gravity and brane probes, valid on timescales short compared to the decay or Poincare recurrence times. Namely de Sitter spacetime dSd(R) in d dimensions with curvature radius R is holographically dual to two conformal field theories on dSd−1(R), cut off at an energy scale 1/R where they couple to each other and to d − 1 dimensional gravity. As part of our analysis, we study brane probes in de Sitter and thermal Anti de Sitter spaces, and interpret the terms in the corresponding DBI action via strongly coupled thermal field theory. This provides a dual field theoretic interpretation of the fact that probes take forever to reach a horizon in general relativity.
TASI/PiTP/ISS Lectures On Moduli and Microphysics
, 2004
"... I review basic forces on moduli that lead to their stabilization, for example in the supercritical and KKLT models of de Sitter space in string theory, as well as an AdS4 × S3 × S3 model I include which is not published elsewhere. These forces come from the classical dilaton tadpole in generic dimen ..."
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Cited by 13 (0 self)
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I review basic forces on moduli that lead to their stabilization, for example in the supercritical and KKLT models of de Sitter space in string theory, as well as an AdS4 × S3 × S3 model I include which is not published elsewhere. These forces come from the classical dilaton tadpole in generic dimensionality, internal curvature, fluxes, and branes and orientifolds as well as nonperturbative effects. The resulting (A)dS solutions of string theory make detailed predictions for microphysical entropy, whose leading behavior we exhibit on the Coulomb branch of the system. Finally, I briefly review recent developments concerning the role of velocitydependent effects in the dynamics of moduli. These lecture notes are based on material presented at various stages in the 1999 TASI, 2002 PiTP, 2003
Spontaneous Creation of Inflationary Universes and the Cosmic Landscape
 JHEP 0409 (2004) 060, arXiv:hepth/0406107; Saswat Sarangi, S.H. Henry Tye, The Boundedness of Euclidean Gravity and the Wavefunction of the Universe, arXiv:hepth/0505104; Saswat Sarangi, S.H. Henry Tye, A Note on the Quantum Creation of Universes, arX
"... Abstract: We study some gravitational instanton solutions that offer a natural realization of the spontaneous creation of inflationary universes in the brane world context in string theory. Decoherence due to couplings of higher (perturbative) modes of the metric as well as matter fields modifies th ..."
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Cited by 10 (5 self)
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Abstract: We study some gravitational instanton solutions that offer a natural realization of the spontaneous creation of inflationary universes in the brane world context in string theory. Decoherence due to couplings of higher (perturbative) modes of the metric as well as matter fields modifies the HartleHawking wavefunction for de Sitter space. Generalizing this new wavefunction to be used in string theory, we propose a principle in string theory that hopefully will lead us to the particular vacuum we live in, thus avoiding the anthropic principle. As an illustration of this idea, we give a phenomenological analysis of the probability of quantum tunneling to various stringy vacua. We find that the preferred tunneling is to an inflationary universe (like our early universe), not to a universe with a very small cosmological constant (i.e., like today’s universe) and not to a 10dimensional uncompactified de Sitter universe. Such preferred solutions are interesting as they offer a cosmological mechanism for the stabilization of extra dimensions during the inflationary