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Eva Silverstein

Publications and source records attributed to Eva Silverstein.

At least 109 records · Page 6Linked to original sources
arXiv2000

Gauge Fields, Scalars, Warped Geometry, and Strings

We review results on several interesting phenomena in warped compactifications of M theory, as presented at Strings 2000. The behavior of gauge fields in dimensional reduction from $d+1$ to $d$ dimensions in various backgrounds is explained from the point of view of the holographic duals (and a point raised in the question session at the conference is addressed). We summarize the role of additional fields (in particular scalar fields) in 5d warped geometries in making it possible for Poincare-invariant domain wall solutions to exist to a nontrivial order in a controlled approximation scheme without fine-tuning of parameters in the $5d$ action (and comment on the status of the singularities arising in the general relativistic description of these solutions). Finally, we discuss briefly the emergence of excitations of wrapped branes in warped geometries whose effective thickness, as measured along the Poincare slices in the geometry, grows as the energy increases.

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arXiv2000

Extended Objects from Warped Compactifications of M Theory

We study the massive spectrum of fully wrapped branes in warped M-theory compactifications, including regimes where these states are parametrically lighter than the Planck scale or string scale. We show that many such states behave classically as extended objects in the noncompact directions in the sense that their mass grows with their size as measured along the Poincare slices making up the noncompact dimensions. On the other hand these states can be quantized in a nontrivial regime: in particular their spectrum of excitations in a limited regime can be obtained by a warped Kaluza-Klein reduction from ten dimensions. We briefly discuss scattering processes and loop effects involving these states, and also note the possibility of an exponential growth in the number of bound states of these objects as a function of energy.

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arXiv2000

Gauge Symmetry and Localized Gravity in M Theory

We discuss the possibility of having gravity ``localized'' in dimension d in a system where gauge bosons propagate in dimension d+1. In such a circumstance - depending on the rate of falloff of the field strengths in d dimensions - one might expect the gauge symmetry in d+1 dimensions to behave like a global symmetry in d dimensions, despite the presence of gravity. Naive extrapolation of warped long-wavelength solutions of general relativity coupled to scalars and gauge fields suggests that such an effect might be possible. However, in some basic realizations of such solutions in M theory, we find that this effect does not persist microscopically. It turns over either to screening or the Higgs mechanism at long distances in the d-dimensional description of the system. We briefly discuss the physics of charged objects in this type of system.

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arXiv2000

Bounds on curved domain walls in 5d gravity

We discuss maximally symmetric curved deformations of the flat domain wall solutions of five-dimensional dilaton gravity that appeared in a recent approach to the cosmological constant problem. By analyzing the bulk field configurations and the boundary conditions at a four-dimensional maximally symmetric curved domain wall, we obtain constraints on such solutions. For a special dilaton coupling to the brane tension that appeared in recent works, we find no curved deformations, confirming and extending slightly a result of Arkani-Hamed et al which was argued using a $Z_2$-symmetry of the solution. For more general dilaton-dependent brane tension, we find that the curvature is bounded by the Kaluza-Klein scale in the fifth dimension.

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arXiv2000

Self-tuning flat domain walls in 5d gravity and string theory

We present Poincare invariant domain wall (``3-brane'') solutions to some 5-dimensional effective theories which can arise naturally in string theory. In particular, we find theories where Poincare invariant solutions exist for arbitrary values of the brane tension, for certain restricted forms of the bulk interactions. We describe examples in string theory where it would be natural for the quantum corrections to the tension of the brane (arising from quantum fluctuations of modes with support on the brane) to maintain the required form of the action. In such cases, the Poincare invariant solutions persist in the presence of these quantum corrections to the brane tension, so that no 4d cosmological constant is generated by these modes.

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arXiv1999

On the Critical Behavior of D1-brane Theories

We study renormalization-group flow patterns in theories arising on D1-branes in various supersymmetry-breaking backgrounds. We argue that the theory of N D1-branes transverse to an orbifold space can be fine-tuned to flow to the corresponding orbifold conformal field theory in the infrared, for particular values of the couplings and theta angles which we determine using the discrete symmetries of the model. By calculating various nonplanar contributions to the scalar potential in the worldvolume theory, we show that fine-tuning is in fact required at finite N, as would be generically expected. We further comment on the presence of singular conformal field theories (such as those whose target space includes a ``throat'' described by an exactly solvable CFT) in the non-supersymmetric context. Throughout the analysis two applications are considered: to gauge theory/gravity duality and to linear sigma model techniques for studying worldsheet string theory.

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arXiv1999

Criteria for Conformal Invariance of (0,2) Models

It is argued that many linear (0,2) models flow in the infrared to conformally invariant solutions of string theory. The strategy in the argument is to show that the effective space-time superpotential must vanish because there is no place where it can have a pole. This conclusion comes from either of two different analyses, in which the Kahler class or the complex structure of the gauge bundle is varied, while keeping everything else fixed. In the former case, we recover from the linear sigma model the usual simple pole in the ${\bf \bar {27}}^3$ Yukawa coupling but show that an analogous pole does not arise in the couplings of gauge singlet modes. In the latter case, a dimension count shows that the world-sheet instanton sum does not ``see'' the singularities of the gauge bundle and hence cannot have a pole.

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arXiv1999

Orientifolds, RG Flows, and Closed String Tachyons

We discuss the fate of certain tachyonic closed string theories from two perspectives. In both cases our approach involves studying directly configurations with finite negative tree-level cosmological constant. Closed string analogues of orientifolds, which carry negative tension, are argued to represent the minima of the tachyon potential in some cases. In other cases, we make use of the fact, noted in the early string theory literature, that strings can propagate on spaces of subcritical dimension at the expense of introducing a tree-level cosmological constant. The form of the tachyon vertex operator in these cases makes it clear that a subcritical-dimension theory results from tachyon condensation. Using results of Kutasov, we argue that in some Scherk-Schwarz models, for finely-tuned tachyon condensates, a minimal model CFT times a subcritical dimension theory results. In some instances, these two sets of ideas may be related by duality.

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arXiv1998

On Vanishing Two Loop Cosmological Constants in Nonsupersymmetric Strings

It has recently been suggested that in certain special nonsupersymmetric type II string compactifications, at least the first two perturbative contributions to the cosmological constant $Λ$ vanish. Support for perturbative vanishing beyond 1-loop (as well as evidence for the absence of some nonperturbative contributions) has come from duality arguments. There was also a direct 2-loop computation which was incomplete; in this note we explain the deficiency of the previous 2-loop calculation and discuss the complete 2-loop computation in two different models. The corrected analysis yields a vanishing 2-loop contribution to $Λ$ in these models.

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arXiv1998

Self-Dual Nonsupersymmetric Type II String Compactifications

It has recently been proposed that certain nonsupersymmetric type II orbifolds have vanishing perturbative contributions to the cosmological constant. We show that techniques of Sen and Vafa allow one to construct dual type II descriptions of these models (some of which have no weakly coupled heterotic dual). The dual type II models are given by the same orbifolds with the string coupling $S$ and a $T^2$ volume $T$ exchanged. This allows us to argue that in various strongly coupled limits of the original type II models, there are weakly coupled duals which exhibit the same perturbative cancellations as the original models.

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arXiv1997

New M-theory Backgrounds with Frozen Moduli

We propose examples, which involve orbifolds by elements of the U-duality group, with M-theory moduli fixed at the eleven-dimensional Planck scale. We begin by reviewing asymmetric orbifold constructions in perturbative string theory, which fix radial moduli at the string scale. Then we consider non-perturbative aspects of those backgrounds (brane probes and the orbifold action from the eleven-dimensional point of view). This leads us to consider mutually non-perturbative group actions. Using a combination of dualities, matrix theory, and ideas for the generalization of the perturbative orbifold prescription, we present evidence that the examples we construct are consistent M-theory backgrounds. In particular we argue that there should be consistent non-supersymmetric compactifications of M-theory.

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arXiv1997

Closing the Generation Gap

I describe recent examples of phase transitions in four-dimensional M theory vacua in which the net generation number changes. There are naive obstructions to transitions lifting chiral matter, but loopholes exist which enable us to avoid them. I first review how chirality arises in the heterotic limit of M theory, previously known forms of topology change in string theory, and chirality-changing phase transitions in six dimensions. This leads to the construction of the four-dimensional examples, which involve wrapped M-theory fivebranes at an $E_8$ wall.

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arXiv1997

Matrix Description of (1,0) Theories in Six Dimensions

We propose descriptions of interacting (1,0) supersymmetric theories without gravity in six dimensions in the infinite momentum frame. They are based on the large N limit of quantum mechanics or 1+1 dimensional field theories with SO(N) gauge group and four supercharges. We argue that this formulation allows for a concrete description of the chirality-changing phase transitions which connect (1,0) theories with different numbers of tensor multiplets.

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arXiv1997

Chirality Changing Phase Transitions in 4d String Vacua

We provide evidence that some four-dimensional N=1 string vacua with different numbers of generations are connected through phase transitions. The transitions involve going through a point in moduli space where there is a nontrivial fixed point governing the low energy field theory. In an M-theory description, the examples involve wrapped 5-branes leaving one of the ends of the world.

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arXiv1997

Zero and One-dimensional Probes with N=8 Supersymmetry

We study the symmetry structure of N=8 quantum mechanics, and apply it to the physics of D0-brane probes in type I' string theory. We focus on the theory with a global $Spin(8)$ R symmetry which arises upon dimensional reduction from $2d$ field theory with $(0,8)$ supersymmetry. There are several puzzles involving supersymmetry which we resolve. In particular, by taking into account the gauge constraint and central charge we explain how the system preserves supersymmetry despite having different numbers of bosonic and fermionic variables. The resulting zero-point energy leads to a linear potential consistent with supersymmetry, and the metric is largely unconstrained. We discuss implications for type I' string theory and the matrix model proposal for M theory.

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arXiv1996

On Gauge Bosons in the Matrix Model Approach to M Theory

We discuss the appearance of $E_8\times E_8$ gauge bosons in Banks, Fischler, Shenker, and Susskind's zero brane quantum mechanics approach to M theory, compactified on the interval $S^1/Z_2$. The necessary bound states of zero branes are proven to exist by a straightforward application of T-duality and heterotic $Spin(32)/Z_2$-Type I duality. We then study directly the zero brane Hamiltonian in Type I' theory. This Hamiltonian includes couplings between the zero branes and background Dirichlet 8 branes localized at the orientifold planes. We identify states, localized at the orientifold planes, with the requisite gauge boson quantum numbers. An interesting feature is that $E_8$ gauge symmetry relates bound states of different numbers of zero branes.

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arXiv1996

Duality, Compactification, and $e^{-1/λ}$ Effects in the Heterotic String Theory

Two classes of stringy instanton effects, stronger than standard field theory instantons, are identified in the heterotic string theory. These contributions are established using type IIA/heterotic and type I/heterotic dualities. They provide examples for the heterotic case of the effects predicted by Shenker based on the large-order behavior of perturbation theory. The corrections vanish as the radius of the compactification goes to infinity. For appropriate amplitudes, they are computable worldsheet or worldline instanton effects on the dual side. Some potential applications are discussed.

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