M. Dine - Chair

M. Dine
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M. Dine
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High Energy Physics - Theory (44)
 
High Energy Physics - Phenomenology (40)
 
High Energy Physics - Lattice (5)
 
High Energy Physics - Experiment (2)
 
Cosmology and Nongalactic Astrophysics (2)

Publications Authored By M. Dine

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 $N_f \ll N$ and $N_f \sim N$). However, there are also striking departures from ordinary QCD and the conventional large $N$ description: instanton effects, when under control, are not exponentially suppressed at large $N$, and branched structure in supersymmetric QCD is always associated with approximate discrete symmetries. Read More

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 {\it natural inflation}. The latter are the actors in (generalized) hybrid inflation. Read More

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. Read More

Landscape analyses often assume the existence of large numbers of fields, $N$, with all of the many couplings among these fields (subject to constraints such as local supersymmetry) selected independently and randomly from simple (say Gaussian) distributions. We point out that unitarity and perturbativity place significant constraints on behavior of couplings with $N$, eliminating otherwise puzzling results. In would-be flux compactifications of string theory, we point out that in order that there be large numbers of light fields, the compactification radii must scale as a positive power of $N$; scaling of the radii and couplings with $N$ may also be necessary for perturbativity. Read More

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 hierarchy problem at the same time. Read More

The possibility of a landscape of metastable vacua raises the question of what fraction of vacua are truly long lived. Naively any would-be vacuum state has many nearby decay paths, and all possible decays must be suppressed. An interesting model of this phenomena consists of $N$ scalars with a random potential of fourth order. Read More

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 CP based on spontaneous CP violation and the Nelson-Barr mechanism. Read More

Naturalness has for many years been a guiding principle in the search for physics beyond the Standard Model, particularly for understanding the physics of electroweak symmetry breaking. However, the discovery of the Higgs particle at 125 GeV, accompanied by exclusion of many types of new physics expected in natural models has called the principle into question. In addition, apart from the scale of weak interactions, there are other quantities in nature which appear unnaturally small and for which we have no proposal for a natural explanation. Read More

Recently it was shown that in QCD-like theories with $N_f > N$, where $N_f$ is the number of light flavors and $N$ is the number of colors, there are correlation functions that vanish in perturbation theory and at short distances receive dominant, calculable contributions from small instantons. Here we extend the set of such objects to theories with $N_f = N$, which includes real QCD, and discuss their application as a calibration of lattice computations at small quark mass. We revisit the related issue of the $u$ quark mass and its additive renormalization by small instantons, and discuss an alternative test of $m_u=0$ on the lattice. Read More

The BICEP2 observations, if confirmed, point to a high scale of inflation and large field excursions during the inflationary era. Non-compact string moduli spaces are a suggestive setting for these phenomena. While unlikely to be described by weak coupling models, one can write down plausible effective field theories compatible with known features of cosmology. Read More

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 number of colors. Read More

We study some consequences of coupling supersymmetric theories to (super)gravity. To linear order, the couplings are determined by the energy-momentum supermultiplet. At higher orders, the couplings are determined by contact terms in correlation functions of the energy-momentum supermultiplet. Read More

This report summarizes the findings of the DPF Theory Panel which was formed with a goal of understanding the scientific problems and opportunities of the next decade, as well as the challenges involved in sustaining a first-class program in theoretical particle physics research in the United States. Read More

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. Read More

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 required in supersymmetric gauge theories with varying number of colors and flavors. Read More

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 SUSY scales, of order $10^{11}$ ($10^9$) GeV for degenerate (mini-split) gauginos and scalars. With flavor structure, the question of whether proton decay or flavor symmetries are more constraining is model-dependent, but it straightforward to find simple models where both constraints are satisfied for much lower SUSY scales. Read More

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-split") spectrum. Read More

Dynamical, metastable supersymmetry breaking appears to be a generic phenomena in supersymmetric field theories. It's simplest implementation is within the so-called "retrofitted O'Raifeartaigh Models". While seemingly flexible, model building in these theories is significantly constrained. Read More

We comment on aspects of discrete anomaly conditions focussing particularly on $R$ symmetries. We review the Green-Schwarz cancellation of discrete anomalies, providing a heuristic explanation why, in the heterotic string, only the "model-independent dilaton" transforms non-linearly under discrete symmetries; this argument suggests that, in other theories, multiple fields might play a role in anomaly cancellations, further weakening any anomaly constraints at low energies. We provide examples in open string theories of non-universal discrete anomalies at low energies. Read More

Most discussion of metastable dynamical supersymmetry breaking (MDSB) has focussed on low energy breaking, as in gauge mediation. It is of interest to consider possible implications for intermediate scale breaking ("gravity mediation"), especially as the early LHC results suggest the possibility that supersymmetry, if broken at relatively low energies, might be tuned. A somewhat high scale for susy breaking could ameliorate the usual flavor problems of gravity mediation, resolve the question of cosmological moduli, and account for a Higgs with mass well above $M_Z$. Read More

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. Read More

We explore some issues in slow roll inflation in situations where field excursions are small compared to $M_p$. We argue that for small field inflation, minimizing fine tuning requires low energy supersymmetry and a tightly constrained structure. Hybrid inflation is {\it almost} an inevitable outcome. Read More

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, which nonetheless differ from those obtained using systematic weak coupling expansions. Read More

If supersymmetry turns out to be a symmetry of nature at low energies, the first order of business to measure the soft breaking parameters. But one will also want to understand the symmetry, and its breaking, more microscopically. Two aspects of this problem constitute the focus of these lectures. Read More

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. Read More

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 question of how moduli are fixed. Read More

Discrete R symmetries are interesting from a variety of points of view. They raise the specter, however, of domain walls, which may be cosmologically problematic. In this note, we describe some of the issues. Read More

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 $N_f>N$, a systematic computation is possible; for $N_fRead More

We prove a general bound on the superpotential in theories with broken supersymmetry and broken R-symmetry, 2|W|< 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 supersymmetry. We briefly discuss several possible applications. Read More

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). Read More

In supersymmetric theories, the presence of axions usually implies the existence of a non-compact, (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 can't be much below 10 MeV; the latter can't be much larger than 10^{13} GeV. Read More

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 theories without and with low energy supersymmetry. Read More

These lectures, given at the Cargese Summer school in 2008, provide an introduction to dynamical supersymmetry breaking and gauge mediation, with emphasis on the recent appreciation of the possible role of metastable supersymmetry breaking, and the evolving understanding of General Gauge Mediation. The underlying focus is on how supersymmetry might be realized at the Large Hadron Collider. Read More

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. Read More

In the landscape, if there is to be any prospect of scientific prediction, it is crucial that there be states which are distinguished in some way. The obvious candidates are states which exhibit symmetries. Here we focus on states which exhibit discrete symmetries. Read More

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, especially the problem of messenger parity and issues connected with R symmetry breaking and CP violation. Read More

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 render states reasonably metastable. Read More

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. Read More

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 only two operators. This provides a highly constrained description of Beyond MSSM (BMSSM) physics. Read More

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 QFT and this particular phenomenon occurs also in supersymmetric theories without gravity. Read More

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 tachyons in the spectrum. Read More

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 classes which, unlike earlier theories, do not have unbroken, approximate $R$ symmetries. Read More

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 the superpotential does. By coupling the system to a pure supersymmetric Yang-Mills theory (or a more general supersymmetric gauge theory with dynamically small vacuum expectation values), these parameters are replaced by powers of its dynamical scale in a way that is naturally enforced by the symmetry. Read More

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 winding tachyons on the size and shape of the barrier and find no evidence at large compactification radius that tachyons enhance the tunneling rate. Read More

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 paper, we discuss situations where these decays are, and are not, suppressed. Read More

In the landscape, states with $R$ symmetries at the classical level form a distinct branch, with a potentially interesting phenomenology. Some preliminary analyses suggested that the population of these states would be significantly suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau spaces based on vanishing polynomials in weighted projective spaces, and find that the suppression is quite substantial. Read More

Three branches of the string theory landscape have plausibly been identified. One of these branches is expected to exhibit a roughly logarithmic distribution of supersymmetry breaking scales. The original KKLT models are in this class. Read More

With respect to the question of supersymmetry breaking, there are three branches of the flux landscape. On one of these, if one requires small cosmological constant, supersymmetry breaking is predominantly at the fundamental scale; on another, the distribution is roughly flat on a logarithmic scale; on the third, the preponderance of vacua are at very low scale. A priori, as we will explain, one can say little about the first branch. Read More

We argue that the study of the statistics of the landscape of string vacua provides the first potentially predictive -- and also falsifiable -- framework for string theory. The question of whether the theory does or does not predict low energy supersymmetry breaking may well be the most accessible to analysis. We argue that low energy -- possibly very low energy -- supersymmetry breaking is likely to emerge, and enumerate questions which must be answered in order to make a definitive prediction. Read More