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Publications (109)
A bstract
The peculiar value of θ is a challenge to the notion of an anthropic landscape. We briefly review the possibility that a suitable axion might arise from an anthropic requirement of dark matter. We then consider an alternative suggestion of Kaloper and Terning that θ might be correlated with the cosmological constant. We note that in a lan...
The peculiar value of $\theta$ is a challenge to the notion of an anthropic landscape. We briefly review the possibility that a suitable axion might arise from an anthropic requirement of dark matter. We then consider an alternative suggestion of Kaloper and Terning that $\theta$ might be correlated with the cosmological constant. We note that in a...
If the QCD axion is a significant component of dark matter, and if the universe was once hotter than a few hundred MeV, the axion relic abundance depends on the function $\chi(T)$, the temperature-dependent topological susceptibility. Uncertainties in this quantity induce uncertainties in the axion mass as a function of the relic density, or vice v...
We study the large $N$ $\theta$ dependence and the $\eta^\prime$ potential in supersymmetric QCD with small soft SUSY-breaking terms. Known exact results in SUSY QCD are found to reflect a variety of expectations from large $N$ perturbation theory, including the presence of branches and the behavior of theories with matter (both with $N_f \ll N$ an...
This talk focuses on the role of light scalars in cosmology, both Nambu-Goldstone bosons and pseudo moduli. The former include QCD axions, which might constitute the dark matter, and more general axions, which, under certain conditions, might play the role of inflatons, implementing natural inflation. The latter are the actors in (generalized) hybr...
We study some aspects of perturbation theory in $N=1$ supersymmetric abelian gauge theories with massive charged matter. In general gauges, infrared (IR) divergences and nonlocal behavior arise in 1PI diagrams, associated with a $1/k^4$ term in the propagator for the vector superfield. We examine this structure in supersymmetric QED. The IR diverge...
We study some aspects of perturbation theory in $N=1$ supersymmetric abelian gauge theories with massive charged matter. In general gauges, infrared (IR) divergences and nonlocal behavior arise in 1PI diagrams, associated with a $1/k^4$ term in the propagator for the vector superfield. We examine this structure in supersymmetric QED. The IR diverge...
Solutions to the strong CP problem typically introduce new scales associated with the spontaneous breaking of symmetries. Absent any anthropic argument for small θ¯these scales require stabilization against ultraviolet corrections. Supersymmetry offers a tempting stabilization mechanism, since it can solve the “big” electroweak hierarchy problem at...
Solutions to the strong CP problem typically introduce new scales associated
with the spontaneous breaking of symmetries. Absent any anthropic argument for
small $\bar\theta$, these scales require stabilization against ultraviolet
corrections. Supersymmetry offers a tempting stabilization mechanism, since it
can solve the "big" electroweak hierarch...
Solutions to strong CP based on chiral structure have been subject to the
most careful scrutiny and critique. Basic theoretical issues include hierarchy
and fine-tuning problems, quality and genericity of symmetries, and
compatibility with solutions to the electroweak hierarchy problem. We study the
similar set of challenges for solutions to strong...
Instanton calculations in QCD are plagued by infrared divergences, and in the
past there has been much discussion of what information they can meaningfully
provide. Here we show that for any number of flavors and colors, including the
phenomenologically relevant case, the short distance behavior of certain
chirality-violating Green's functions is c...
The discovery of a large tensor-to-scalar ratio by the BICEP2 experiment
points to large field excursions during inflation. One framework that predicts
large $r$ is monodromy inflation. While discussed mainly in the context of
string theory, the phenomenon can be illustrated and studied in the
well-understood framework of SUSY QCD with a large numb...
It is sometimes argued that a virtue of pushing the supersymmetry breaking scale above 1 PeV is that no particular flavor structure is required in the soft sector in order to evade bounds on flavor-changing neutral currents. However, without flavor structure, suppressing generic Planck-suppressed contributions to proton decay requires even higher S...
It is sometimes stated that $n_s = 0.98$ in hybrid inflation; sometimes that
it predicts $n_s >1$. A number of authors have consider aspects of Planck scale
corrections and argued that they affect these predictions. Here we consider
these systematically, describing the situations which can yield $n_s =0.96$,
and the extent to which this result requ...
The phenomenon known as "anomaly mediation" can be understood in a variety of
ways. Rather than an anomaly, certain gaugino bilinear terms are required by
local supersymmetry and gauge invariance (the derivation of these terms is in
some cases related to anomalies in scale invariance or $R$ symmetries). We
explain why the gaugino bilinear is requir...
It is sometimes argued that a virtue of pushing the supersymmetry breaking
scale above 1 PeV is that no particular flavor structure is required in the
soft sector in order to evade bounds on flavor-changing neutral currents.
However, without flavor structure, suppressing generic Planck-suppressed
contributions to proton decay requires even higher S...
Supersymmetry and string theory suggest the existence of light moduli. Their presence, or absence, controls the realization of supersymmetry at low energies. If there are no such fields, or if all such fields are fixed in a supersymmetric fashion, the conventional thermal production of lightest supersymmetric particle dark matter is possible, as is...
Supersymmetry and string theory suggest the existence of light moduli. Their
presence, or absence, controls the realization of supersymmetry at low
energies. If there are no such fields, or if all such fields are fixed in a
supersymmetric fashion, the conventional thermal production of LSP dark matter
is possible, as is an anomaly-mediated ("mini-s...
Recently, questions have been raised about the role of Lorentz invariance in
false vacuum decay. It has been argued that infinities may arise in an
integration over Lorentz-boosted final states. This suggestion motivates a
Minkowski-space analysis of the decay rate. We attempt to illuminate features
of the amplitude computation, and argue that the...
We explore some issues in slow roll inflation in situations where field excursions are
small compared to Mp. We argue that for small field inflation, minimizing fine tuning requires low energy
supersymmetry and a tightly constrained structure. Hybrid inflation
is almost an inevitable outcome. The resulting theory can be described in terms of a supe...
We revisit two longstanding puzzles in supersymmetric gauge theories. The
first concerns the question of the holomorphy of the coupling, and related to
this the possible definition of an exact (NSVZ) beta function. The second
concerns instantons in pure gluodynamics, which appear to give sensible, exact
results for certain correlation functions, wh...
While axions seem ubiquitous in critical string theories, whether they might survive in any string theoretic description of nature is a difficult question. With some mild assumptions, one can frame the issues in the case that there is an approximate supersymmetry below the underlying string scale. The problem of axions is then closely tied to the q...
This article reviews the subject of supersymmetry and its breaking. The
emphasis is on recent developments in metastable, dynamical supersymmetry
breaking, which permit the construction of promising models of particle
physics.
We revisit the question of whether or not one can perform reliable semiclassical QCD computations at zero temperature. We study correlation functions with no perturbative contributions, and organize the problem by means of the operator product expansion, establishing a precise criterion for the validity of a semiclassical calculation. For $N_f>N$,...
We prove a general bound on the superpotential in theories with broken supersymmetry and broken R-symmetry, |〈W〉| < \( \frac{1}{2} \)
f
a
F, where f
a
and F are the R-axion and Goldstino decay constants, respectively. The bound holds for weakly coupled as well as strongly coupled theories, thereby providing an exact result in theories with broken s...
If nature exhibits low energy supersymmetry, discrete (non-$Z_2$) R symmetries may well play an important role. In this paper, we explore such symmetries. We generalize gaugino condensation, constructing large classes of models which are classically scale invariant, and which spontaneously break discrete R symmetries (but not supersymmetry). The or...
In supersymmetric theories, the presence of axions usually implies the existence of a noncompact, (pseudo)moduli space. In gauge-mediated models, the axion would seem a particularly promising dark matter candidate. The cosmology of the moduli then constrains the gravitino mass and the axion decay constant; the former cannot be much below 10 MeV; th...
Invoking the Peccei-Quinn (PQ) solution to the strong CP problem substitutes the puzzle of why $\theta_{qcd}$ is so small with the puzzle of why the PQ symmetry is of such high quality. Cosmological and astrophysical considerations raise further puzzles. This paper explores this issues in several contexts: string theory and field theory, and theori...
Supersymmetric vacua are stable. It is interesting to ask: how long-lived are vacua which are nearly supersymmetric? This question is relevant if our universe is approximately supersymmetric. It is also of importance for a number of issues of the physics of the landscape and eternal inflation. In this note, we distinguish a variety of cases. In all...
Recently there has been much progress in building models of gauge mediation, often with predictions different than those of minimal gauge mediation. Meade, Seiberg, and Shih have characterized the most general spectrum which can arise in gauge mediated models. We discuss some of the challenges of building models of General Gauge Mediation, especial...
Recently there has been much progress in building models of gauge mediation, often with predictions different than those of minimal gauge mediation. Meade, Seiberg, and Shih have characterized the most general spectrum which can arise in gauge mediated models. We discuss some of the challenges of building models of General Gauge Mediation, especial...
We argue that the vast majority of flux vacua with small cosmological
constant are unstable to rapid decay to a big crunch. Exceptions
are states with large compactification
volume and supersymmetric and approximately supersymmetric states. Neither
weak string coupling, warping, or the existence of very light
particles are, by themselves, enough
to...
Dynamical breaking of supersymmetry was long thought to be an exceptional phenomenon, but recent developments have altered this view. A question of great interest in the current framework is the value of the underlying scale of supersymmetry breaking. The "little hierarchy" problem suggests that supersymmetry should be broken at low energies. Withi...
We interpret the current experimental limit on the lightest Higgs boson mass to suggest that if nature is supersymmetric, there are additional interactions beyond those of the MSSM coming from new degrees of freedom around the TeV scale. Within an effective field theory analysis, the leading order corrections to the MSSM are described in terms of o...
Scherk-Schwarz compactification in string theory can be defined as orbifolding by an R symmetry, a symmetry that acts differently on bosons and fermions. Such a symmetry can arise in many situations, including toroidal and orbifold compactifications, as well as smooth Calabi-Yau spaces. If the symmetry acts freely then for large radius there are no...
We elucidate the physics
underlying ``anomaly mediation'', giving several alternative
derivations of the formulas for gaugino and scalar masses. We
stress that this phenomenon is of a type familiar in field theory,
and does not represent an anomaly, nor does it depend on
supersymmetry breaking and its mediation. Analogous phenomena are
common in QF...
Until recently, dynamical supersymmetry breaking seemed an exceptional phenomenon, involving chiral gauge theories with a special structure. Recently it has become clear that requiring only metastable states with broken supersymmetry leads to a far broader class of theories. In this paper, we extend these constructions still further, finding new cl...
We provide a method for obtaining simple models of supersymmetry breaking, with all small mass scales generated dynamically, and illustrate it with explicit examples. We start from models of perturbative supersymmetry breaking, such as O’Raifeartaigh and Fayet models, that would respect an R symmetry if their small input parameters transformed as t...
We investigate, from a spacetime perspective, some aspects of Horowitz's recent conjecture that black strings may catalyze the decay of Kaluza-Klein spacetimes into a bubble of nothing. We identify classical configurations that interpolate between flat space and the bubble, and discuss the energetics of the transition. We investigate the effects of...
One proposed solution of the moduli problem of string cosmology requires that the moduli are quite heavy, their decays reheating the Universe to temperatures above the scale of nucleosynthesis. In many of these scenarios, the moduli are approximately supersymmetric; it is then crucial that the decays to gravitinos are helicity suppressed. In this p...
We revisit some questions in supersymmetric hybrid inflation (SHI). We analyze the amount of fine tuning required in various models, the problem of decay at the end of inflation and the generation of baryons after inflation. We find that the most natural setting for HI is in supersymmetric models with non-renormalizable couplings. Furthermore, we a...
We initiate a search for non-perturbative consistency conditions in M theory. Some non-perturbative conditions are already known in Type I theories; we review these and search for others. We focus principally on possible anomalies in discrete symmetries. It is generally believed that discrete symmetries in string theories are gauge symmetries, so a...
There has been some debate as to whether the landscape does
or does not predict low energy supersymmetry. We argue that under
rather mild assumptions, the landscape seems to favor such breaking,
quite possibly at a very low scale. Some of the issues which must
be addressed in order to settle these questions are the relative
frequency with which tre...
Witten long ago pointed out that the simplest Kaluza-Klein theory, without supersymmetry, is subject to a catastrophic instability. There are a variety of string theories which are potentially subject to these instabilities. Here we explore a number of questions: how generic are these instabilities? what happens when a potential is generated on the...
The nature of axion cosmology is usually said to depend on whether the Peccei–Quinn
(PQ) symmetry breaks before or after inflation. The PQ symmetry itself is believed to be
an accident, so there is not necessarily a symmetry during inflation at all. We explore these
issues in some simple models, which provide examples of symmetry breaking before an...
We examine recent claims of a large set of flux compactification solutions of string theory. We conclude that the arguments for AdS solutions are plausible. The analysis of meta-stable dS solutions inevitably leads to situations where long distance effective field theory breaks down. We then examine whether these solutions are likely to lead to a d...
If low energy supersymmetry is realized in nature it is possible that a first generation linear collider will only have access to some of the superpartners with electroweak quantum numbers. Among these, sleptons can provide sensitive probes for lepton flavor violation through potentially dramatic lepton violating signals. Theoretical proposals to u...
The decay constant of the QCD axion is required by observation to be small compared to the Planck scale. In theories of "natural inflation," and certain proposed anthropic solutions of the cosmological constant problem, it would be interesting to obtain a large decay constant for axion-like fields from microscopic physics. String theory is the only...
Closed string tachyons have long been somewhat
mysterious. We note that there is often a regime in the classical
moduli space in which one can systematically compute the effective
action for such fields. In this regime, the tachyon is light, and
cannot be integrated out. Instead, one must consider the combined
dynamics of gravitons, moduli, tachyon...
We study the consequences of time variations in the scale of grand unification, $M_U$, when the Planck scale and the value of the unified coupling at the Planck scale are held fixed. We show that the relation between the variations of the low energy gauge couplings is highly model dependent. It is even possible, in principle, that the electromagnet...
We study grand unified theories based on an SU(5)xSU(5) gauge group in which the GUT scale, M_{GUT}, is the VEV of an exact or approximate modulus, and in which fast proton decay is avoided through a combination of a large triplet mass and small triplet couplings. These features are achieved by discrete symmetries. In many of our models, M_{GUT} is...
In brane world models of nature, supersymmetry breaking is often isolated on a distant brane in a higher dimensional space. The form of the Kähler potential in generic string and M-theory brane world backgrounds is shown to give rise to tree-level nonuniversal squark and slepton masses. This results from the exchange of bulk supergravity fields and...
We argue that models in which an observable variation of the fine structure constant is explained by motion of a cosmic scalar field are not stable under renormalization and require massive fine-tuning that cannot be explained by any known mechanism.
It is natural to ask whether noncommutative geometry plays a role in four dimensional physics. By performing explicit computations in various toy models, we show that quantum effects lead to violations of Lorentz invariance at the level of operators of dimension three or four. The resulting constraints are very stringent.
String and M-theory realizations of brane world supersymmetry breaking scenarios are considered in which visible sector Standard Model fields are confined on a brane, with hidden sector supersymmetry breaking isolated on a distant brane. In calculable examples with an internal manifold of any volume the Kahler potential generically contains brane--...
In brane world models of nature, supersymmetry breaking is often isolated on a distant brane in a higher dimensional space. The form of the Kahler potential in generic string and M-theory brane world backgrounds is shown to give rise to tree-level non-universal squark and slepton masses. This results from the exchange of bulk supergravity fields an...
The apparent observation of dark energy poses problems for string theory. In de Sitter space, or in quintessence models, one cannot define a gauge-invariant S-matrix. We argue that eternal quintessence does not arise in weakly coupled string theory, but point out that it is difficult to define an $S$-matrix even in the presence of perturbative pote...
Supersymmetric models with a high supersymmetry breaking scale give, in general, large contributions to ɛK and/or to various electric dipole moments, even when contributions to CP conserving, flavor changing processes are sufficiently suppressed. Some examples are models of dilaton dominance, alignment, non-Abelian flavor symmetries, heavy first tw...
There are only a small number of ideas for stabilizing the moduli of string theory. One of the most appealing of these is the racetrack mechanism, in which a delicate interplay between two strongly interacting gauge groups fixes the value of the coupling constant. In this paper, we explore this scenario. We find that, quite generally, some number o...
Motivated by recent developments, we explore some issues in Affleck–Dine baryogenesis. We consider in greater detail the role of thermal effects in the production of baryon number. We find that these effects are important even for rather flat potentials, and obtain somewhat different estimates of the baryon asymmetry than those in the literature. W...
Motivated by recent work of Bousso and Polchinski (BP), we study theories which explain the small value of the cosmological constant using the anthropic principle. We argue that simultaneous solution of the gauge hierarchy problem is a strong constraint on any such theory. We exhibit three classes of models which satisfy these constraints. The firs...
There are at least two serious moduli problems in string cosmology. The first is the possibility that moduli dominate the energy density at the time of nucleosynthesis. The second is that they may not find their minima all together. After reviewing some previously proposed solutions to these problems, we propose another: all of the moduli but the d...
Recently, a number of authors have challenged the conventional assumption that the string scale, Planck mass, and unification scale are roughly comparable. It has been suggested that the string scale could be as low as a TeV. In this note, we explore constraints on these scenarios. We argue that the most plausible cases have a fundamental scale of...
It has recently been shown that the Matrix model and supergravity give the same predictions for three-graviton scattering. This contradicts an earlier claim in the literature. We explain the error in this earlier work, and go on to show that certain terms in the n-graviton scattering amplitude involving v2n are given correctly by the Matrix model....
It has recently been shown that the Matrix model and supergravity give the same predictions for three graviton scattering. This contradicts an earlier claim in the literature (hep-th/9710174). We explain the error in this earlier work, and go on to show that certain terms in the $n$-graviton scattering amplitude involving $v^{2n}$ are given correct...
The ground state of string theory may lie at a point of “maximally enhanced symmetry", at which all of the moduli transform under continuous or discrete symmetries. This hypothesis, along with the hypotheses that the theory at high energies has N=1 supersymmetry and that the gauge couplings are weak and unified, has definite consequences for low en...
Baryogenesis from the coherent production of a scalar condensate along a flat direction of the supersymmetric extension of the standard model (Aflleck-Dine mechanism) is investigated. Two important effects are emphasized. First, non-renormalizable terms in the superpotential can lift standard model flat directions at large field values. Second, the...
M-theory is believed to be described in various dimensions by large N field theories. It has been further conjectured that at finite N, these theories describe the discrete light cone quantization (DLCQ) of M theory. Even at low energies, this is not necessarily the same thing as the DLCQ of supergravity. It is believed that this is only the case f...
M$-theory is believed to be described in various dimensions by large $N$ field theories. It has been further conjectured that at finite $N$, these theories describe the discrete light cone quantization (DLCQ) of $M$ theory. Even at low energies, this is not necessarily the same thing as the DLCQ of supergravity. It is believed that this is only the...
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...
We study the leading irrelevant operators along the flat directions of certain supersymmetric theories. In particular, we focus on finite N = 2 (including N = 4) supersymmetric field theories in four dimensions and show that these operators are completely determined by the symmetries of the problem. This shows that they are generated only at one lo...
The experimental signatures for low energy supersymmetry breaking are presented. The lightest standard model superpartner is unstable and decays to its partner plus a Goldstino, G. For a supersymmetry breaking scale below a few 1000 TeV this decay can take place within a detector, leading to very distinctive signatures. If a neutralino is the light...
String theory possesses numerous axion candidates. The recent realization that the compactification radius in string theory might be large means that these states can solve the strong CP problem. This still leaves the question of the cosmological bound on the axion mass. Here we explore two schemes for accommodating such light axions in cosmology....
We study various modifications to the minimal models of gauge mediated supersymmetry breaking. We argue that, under reasonable assumptions, the structure of the messenger sector is rather restricted. We investigate the effects of possible mixing between messenger and ordinary squark and slepton fields and, in particular, violation of universality....
For a long time, it has been widely assumed that if the underlying laws of nature are supersymmetric, supersymmetry is broken at a scale intermediate between the weak scale and the Planck mass. The construction of realistic models of dynamical supersymmetry breaking in which supersymmetry is broken at a much lower scale, as well as a growing apprec...
If nature is described by string theory, and if the compactification radius is large (as suggested by the unification of couplings), then the theory is in a regime best described by the low energy limit of M-theory. We discuss some phenomenological aspects of this view. The scale at which conventional quantum field theory breaks down is of order th...
String theory, if it describes nature, is probably strongly coupled. In light of recent developments in string duality, this means that the “real world” should correspond to a region of the classical moduli space which admits no weak coupling description. We exhibit, in the heterotic string, one such region of the moduli space, in which the couplin...
String theory, if it describes nature, is probably strongly coupled. In light of recent developments in string duality, this means that the ``real world'' should correspond to a region of the classical moduli space which admits no weak coupling description. We exhibit, in the heterotic string, one such region of the moduli space, in which the coupl...
The experimental signatures for gauge mediated supersymmetry breaking are presented. The phenomenology associated with this class of models is distinctive since the gravitino is naturally the LSP. The next lightest supersymmetric particle (NLSP) can be a gaugino, Higgsino, or right handed slepton. Decay of the NLSP to its partner plus the LSP proce...
The experimental signatures for gauge mediated supersymmetry breaking are presented. The phenomenology associated with this class of models is distinctive since the gravitino is naturally the LSP. The next lightest supersymmetric particle (NLSP) can be a gaugino, Higgsino, or right handed slepton. Decay of the NLSP to its partner plus the LSP proce...
Generically, string models with $N=1$ supersymmetry are not expected to have moduli beyond perturbation theory; stringy non-perturbative effects as well as low energy field-theoretic phenomena such as gluino condensation will lift any flat directions. In this note, we describe models where some subspace of the moduli space survives non-perturbative...
We report the construction of large new classes of models which break supersymmetry dynamically. We then turn to model building. Two of the principal obstacles to constructing simple models of dynamical supersymmetry breaking are the appearance of Fayet-Iliopoulos D terms and difficulties in generating a $\mu$ term for the Higgs fields. Among the n...
Supersymmetry breaking in the early universe induces scalar soft potentials with curvature of order the Hubble constant. This has a dramatic effect on the coherent production of scalar fields along flat directions. For the moduli problem it generically gives a concrete realization of the problem by determining the field value subsequent to inflatio...
Electroweak baryogenesis can occur in the “adiabatic limit”, in which expanding bubbles of true vacuum are assumed to have rather thick walls and be slowly moving. Here the problem of calculating the baryon asymmetry in this limit is reconsidered. A simple prescription for obtaining the relevant kinetic equations is given. An additional suppression...
The technibaryon constitute a possible dark matter candidate. Such a particle with electroweak quantum numbers is already nearly ruled out as the dominant component of the galactic dark matter by nuclear recoil experiments. Here, the scattering of singlet technibaryons, without electroweak quantum numbers, is considered. For scalar technibaryons th...
Conventional approaches to supersymmetric model building suffer from several naturalness problems: they do not explain the large hierarchy between the weak scale and the Planck mass, and they require fine tuning to avoid large flavor changing neutral currents and particle electric dipole moments. The existence of models with dynamical supersymmetry...
Perturbation theory at finite temperature suffers from well-known infrared
problems. In the standard model, as a result, one cannot calculate the
effective potential for arbitrarily small values of $\phi$, the Higgs
expectation value. Because the Higgs field is now known not to be extremely
light, it is necessary to determine whether perturbation t...
We exhibit a novel solution of the strong CP problem, which does not involve any massless particles. The low energy effective lagrangian of our model involves a discrete space-time independent axion field which can be thought of as a parameter labeling a dense set of θ vacua. In the full theory this parameter is seen to be dynamical, and the model...
We use a Schrödinger picture version of the instanton calculus to analyze the suggestion that nonperturbative instanton effects, such as baryon number violation in the electroweak interaction, can become large in high-energy scattering. We confirm that the euclidean instanton results of Ringwald, Espinosa and others are correct, for models with ins...
We explore a suggestion that baryon number violation is unsuppressed in the standard model at high energies and temperatures. We find that baryon number violation is negligible in high energy scattering. On the other hand, in agreement with previous authors, we find that it is indeed unsuppressed at high temperatures. We give simple, qualitative ar...
In the superconformal field theory approach to superstrings, the space-time supersymmetry is not manifest. In contrast, conventional four-dimensional N = 1 supersymmetric field theories admit a superspace formulation that easily reveals consequences of supersymmetry for these theories, such as nonrenormalization theorems. The existence of auxiliary...
Some aspects of monopoles in string theory are considered. Three cases are described where monopole solutions can be constructed in a systematic approximation scheme. The lowest order solutions are exhibited for these examples, as well as certain higher order corrections. Issues involved in a proper string theoretic treatment of these solutions, su...
String theory exhibits a number of string miracles. These are “accidental” relations between couplings in the low-energy effective action which cannot be understood in terms of the symmetries of that action. It is shown that the existence of (0, 2) models need not be a string miracle, but can often be understood in terms of a discrete R symmetry. T...
Many questions about the detailed microscopic properties of string
theories can be addressed by focusing on the interactions of the
massless states after integrating out the massive modes. We explain the
connection of this wilsonian approach in spacetime to the wilsonian view
of the renormalization group on the world-sheet, and use this viewpoint
t...
It has been argued that Fayet-Iliopoulos D terms should appear in the
effective low-energy lagrangian of certain superstring
compactifications. If present, these break supersymmetry and lead to
certain scalar mass terms at one loop, and to a dilaton tadpole at two
loops. In this note we show that the expected effects are indeed present
at one loop,...
Superspace formulations of the most general two-dimensional sigma models with (2,0) and (2,1) supersymmetry are constructed and some of their implications discussed.
The axion solution to the strong CP problem is reexamined. It is noted that in order for the axion to solve the problem, it is necessary that high-energy contributions to the axion potential be sufficiently small. Examples are constructed where this is not the case. It is noted that this problem arises in many interesting compactifications of strin...
It is now established that the non-renormalization theorems are violated by non-perturbative effects in many four-dimensional supersymmetric theories, and that dynamical supersymmetry-breaking (DSB) occurs in some chiral gauge theories. Here we presenr a set of general techniques which allow one to determine whether or not supersymmetry is broken i...
We argue that if the superstring is to describe our world, it is probably strongly coupled. Several other (unlikely) possibilities are discussed. Supported in part by the U.S. Department of Energy through grant no. DE-AC02-76ER02220.