arXiv subjects

Michael Dine

Publications and source records attributed to Michael Dine.

At least 109 records · Page 6Linked to original sources

arXiv1999

Constraints on Theories With Large Extra Dimensions

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 at least 10 TeV and five dimensions of inverse size 10 MeV. We show that a radial dilaton mass in the range of proposed millimeter scale gravitational arises naturally in these scenarios. Most other scenarios require huge values of flux and may not be realizable in M Theory. Existing precision experiments put a conservative lower bound of 6-10 TeV on the fundamental energy scale. We note that large dimensions with bulk supersymmetry might be a natural framework for quintessence, and make some other tentative remarks about cosmology.

hep-th↗

arXiv1999

Seeking the Ground State of String Theory

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. The greatest obstacle to developing a string phenomenology is our lack of understanding of the ground state. We explain why the dynamics which determines this state is not likely to be accessible to any systematic approximation. We note that the racetrack scheme, often cited as a counterexample, suffers from similar difficulties. We stress that the weakness of the gauge couplings, the gauge hierarchy, and coupling unification suggest that it may be possible to extract some information in a systematic approximation. We review the ideas of Kahler stabilization, an attempt to reconcile these facts. We consider whether the system is likely to sit at extremes of the moduli space, as in recent proposals for a low string scale. Finally we discuss the idea of Maximally Enhanced Symmetry, a hypothesis which is technically natural, compatible with basic facts about cosmology, and potentially predictive.

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arXiv1999

Tree Level Supergravity and 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 correctly by the Matrix model. The Matrix model also generates certain $v^6$ terms in four graviton scattering at three loops, which do not seem to have any counterparts in supergravity. The connection of these results with nonrenormalization theorems is discussed.

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arXiv1998

Renormalization of Higher Derivative Operators in the Matrix Model

$M$-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 for quantities which are protected by non-renormalization theorems. In 0+1 and 1+1 dimensions, we provide further evidence of a non-renormalization theorem for the $v^4$ terms, but also give evidence that there are not such theorems at order $v^8$ and higher.

hep-th↗

arXiv1998

Enhanced Symmetries and the Ground State of String Theory

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 energy physics. We describe these, and offer some suggestions as to how these assumptions might be compatible.

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arXiv1998

Dynamical supersymmetry breaking in models with a Green-Schwarz mechanism

We consider supersymmetry breaking in theories with gaugino condensation in the presence of an anomalous U(1) symmetry with anomaly cancellation by the Green-Schwarz mechanism. In these models, a Fayet-Iliopoulos D-term can give important contributions to the soft supersymmetry-breaking scalar masses. Most discussions of this possibility have ignored the dilaton field. We argue that this is not appropriate in general, and show that the F-term contributions to the soft breaking terms are comparable to or much larger than the D-term contributions, depending on how the dilaton is stabilized. We discuss phenomenological implications of these results.

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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

Some Issues in Gauge Mediation

After briefly reviewing some arguments in favor of high scale and low scale supersymmetry breaking, I discuss a possible solution of the $μ$-problem of gauge mediated models.

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arXiv1997

An Inflaton Candidate in Gauge Mediated Supersymmetry Breaking

Inflation, as currently understood, requires the presence of fields with very flat potentials. Supersymmetric models in which supersymmetry breaking is communicated by supergravity naturally yield such fields, but the scales are typically not suitable for obtaining both sufficient inflation and a suitable fluctuation spectrum. In the context of recent ideas about gauge mediation, there are new candidates for the inflaton. We present a simple model for slow-rollover inflation where the vacuum energy driving inflation is related to the same F-term responsible for the spectrum of supersymmetric particles in gauge mediated supersymmetry breaking models. The inflaton is identified with field responsible for the generation of the $μ$-term\. This opens the possibility of getting some knowledge about the low-energy supersymmetric theory from measurements of the cosmic microwave background radiation. Gravitinos do not pose a cosmological problem, while the moduli problem is ameliorated.

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arXiv1997

Comments on Higher Derivative Operators in Some SUSY Field Theories

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 loop and are not renormalized beyond this order. An instanton computation in similar three dimensional theories shows that these terms are renormalized. Hence, the four dimensional non-renormalization theorem of these terms is not valid in three dimensions.

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arXiv1996

Supersymmetry Phenomenology With a Broad Brush

These lectures provide an introduction to supersymmetry phenomenology. They include an overview of the Minimal Supersymmetric Standard Model. The notion of soft breaking is explained, constraints on the standard soft breaking parameters are reviewed, and the standard ansatz of universal soft masses is discussed. The rest of the lectures are devoted to understanding supersymmetry breaking more microscopically. Models of dynamical supersymmetry breaking are reviewed, after which we turn to the question of the scale of supersymmetry breaking. Both intermediate and low scales and their phenomenology are considered. Finally, we consider applications to string theory. The emphasis, throughout, is on general issues rather then extensive detail, but it is hoped that the listeners/readers will be prepared after these lectures to delve into the details.

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arXiv1996

Some Non-Renormalization Theorems for Higher Derivative Operators

It has been argued that a certain large $N$ matrix model may provide a non-perturbative definition of $M$-theory. This model is the truncation to $0+1$ dimensions of ten-dimensional supersymmetric Yang-Mills theory. It is crucial to this identification that terms with four derivatives in the effective action for the quantum mechanics should not be renormalized. We offer a perturbative proof of this result.

hep-th↗

arXiv1996

String Theory Dualities

The past year has seen enormous progress in string theory. It has become clear that all of the different string theories are different limits of a single theory. Moreover, in certain limits, one obtains a new, eleven-dimensional structure known as $M$-theory. Strings with unusual boundary conditions, known as D-branes, turn out to be soliton solutions of string theory. These have provided a powerful tool to probe the structure of these theories. Most dramatically, they have yielded a partial understanding of the thermodynamics of black holes in a consistent quantum mechanical framework. In this brief talk, I attempt to give some flavor of these developments.

hep-th↗

arXiv1996

The Cosmology of String Theoretic Axions

String theory posesses 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. In the first, we note that in string theory the universe is likely to be dominated early on by the coherent oscillations of some moduli. The usual moduli problem assumes that these fields have masses comparable to the gravitino. We argue that string moduli are likely to be substantially more massive, eliminating this problem. In such cosmologies the axion bound is significantly weakened. Plausible mechanisms for generating the baryon number density are described. In the second, we point out that in string theory, the axion potentials might be much larger at early times than at present. In string theory, if CP violation is described by a small parameter, the axion may sit sufficiently close to its true minimum to invalidate the bounds.

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arXiv1996

Variations on Minimal Gauge Mediated Supersymmetry Breaking

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. We show that acceptable values for the $μ$ and $B$ parameters can naturally arise from discrete, possibly horizontal, symmetries. We claim that in models where the supersymmetry breaking parameters $A$ and $B$ vanish at tree level, $\tanβ$ could be large without fine tuning. We explain how the supersymmetric CP problem is solved in such models.

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arXiv1996

Phenomenological Implications of Low Energy Supersymmetry Breaking

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 lightest standard model superpartner it decays by $χ_1^0 \to γ+ G$, and if kinematically accessible by $χ_1^0 \to (Z^0, h^0, H^0, A^0) + G$. These decays can give rise to displaced vertices. Alternately, if a slepton is the lightest standard model superpartner it decays by $\tilde{l} \to l + G$. This can be seen as a greater than minimum ionizing charged particle track, possibly with a kink to a minimum ionizing track.

hep-ph↗

arXiv1996

What is the Scale of Supersymmetry Breaking

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 appreciation of the supersymmetric flavor problem has reopened this question. After reviewing some ideas for understanding the microscopic origin of the soft breaking parameters in the context of string theory, I turn to low energy breaking. Independent of the details of the underlying theory, events with photons and missing energy, like the CDF $e^+e^-γγ\not{E}_T$ event, are likely signals of low energy breaking. I briefly review the predictions of the simplest model of low energy supersymmetry breaking for the soft breaking parameters (MGM), and then ask what sorts of generalizations are possible. It turns out that if all couplings are weak, there are only a limited number of ways to modify the model.

hep-ph↗

arXiv1996

Experimental Signatures of Low Energy Gauge Mediated Supersymmetry Breaking

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 proceeds through the Goldstino component of the gravitino. For a significant range of parameters this decay can take place within the detector, and can be measured as a displaced vertex or kink in a charged particle track. In the case that the NLSP is mostly gaugino, we identify the discovery modes as $e^+e^- \rightarrow γγ+ \Emiss$, and $p \bar{p} \rightarrow l^+ l^- γγ+ \EmissT$. If the NLSP is a right handed slepton the discovery modes are $e^+ e^- \rightarrow l^+ l^- + \Emiss$ and $p \bar{p} \rightarrow l^+ l^- + \EmissT$. An NLSP which is mostly Higgsino is also considered. Finally, these theories can contain scalar particles which mediate sub-millimeter range coherent forces of gravitational strength.

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