arXiv subjects

Michael Dine

Publications and source records attributed to Michael Dine.

At least 127 records · Page 7Linked to original sources

arXiv1996

Couplings and Scales in Strongly Coupled Heterotic String Theory

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 the unification scale and consequently (approximate) discrete symmetries are essential to prevent proton decay. There are one or more light axions, one of which solves the strong CP problem. Modular cosmology is still problematic but much more complex than in perturbative string vacua. We also consider a range of more theoretical issues, focusing particularly on the question of stabilizing the moduli. We give a simple, weak coupling derivation of Witten's expression for the dependence of the coupling constants on the eleven dimensional radius. We discuss the criteria for the validity of the long wavelength analysis and find that the "real world" seems to sit just where this analysis is breaking down. On the other hand, residual constraints from N=2 supersymmetry make it difficult to see how the moduli can be stabilized while at the same time yielding a large hierarchy.

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arXiv1996

Truly Strong Coupling and Large Radius in String Theory

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 coupling, $λ$, is large and the ``compactification radius'' scales as $λ^{1/3}$. We discuss some of the issues raised by the conjecture that the true vacuum lies in such a region. These include the question of coupling constant unification, and more generally the problem of what quantities one might hope to calculate and compare with experiment in such a picture.

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arXiv1995

Quantum Moduli Spaces of $N=1$ String Theories

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-perturbatively. Discrete $R$ symmetries forbid any inherently stringy effects, and dynamical considerations control the field-theoretic effects. The surviving subspace is a space of high symmetry; the system is attracted to this subspace by a potential which we compute. Models of this type may be useful for considerations of duality and raise troubling cosmological questions about string theory. Our considerations also suggest a mechanism for fixing the expectation value of the dilaton.

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arXiv1995

Coming to Terms with Strongly Coupled Strings

The holomorphy of the superpotential along with symmetries gives very strong constraints on any stringy non-perturbative effects. This observation suggests an approach to string phenomenology. (Presented at ``Strings 95'', March 1995.

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arXiv1995

New Tools for Low Energy Dynamical Supersymmetry Breaking

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 $μ$ term for the Higgs fields. Among the new models are examples in which symmetries prevent the appearance of Fayet-Iliopoulos terms. A gauge singlet field, that may play a role in explaining the hierarchy in quark and lepton parameters, can generate a suitable $μ$ term. The result is a comparatively simple model, with a low energy structure similar to that of the MSSM, but with far fewer arbitrary parameters. We begin the study of the phenomenology of these models.

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arXiv1995

Baryogenesis from Flat Directions of the Supersymmetric Standard Model

Baryogenesis from the coherent production of a scalar condensate along a flat direction of the supersymmetric extension of the standard model (Affleck-Dine mechanism) is investigated. Two important effects are emphasized. First, nonrenormalizable terms in the superpotential can lift standard model flat directions at large field values. Second, the finite energy density in the early universe induces soft potentials with curvature of order the Hubble constant. Both these have important implications for baryogenesis, which requires large squark or slepton expectation values to develop along flat directions. In particular, the induced mass squared must be negative. The resulting baryon to entropy ratio is very insensitive to the details of the couplings and initial conditions, but depends on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction and the reheat temperature after inflation. Unlike the original scenario, an acceptable baryon asymmetry can result without subsequent entropy releases. In the simplest scenario the baryon asymmetry is generated along the $LH_u$ flat direction, and is related to the mass of the lightest neutrino.

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arXiv1995

Supersymmetry Breaking in the Early Universe

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 inflation. However it might suggest a solution if the minimum of the induced potential coincides with the true minimum. The induced Hubble scale mass also has important implications for the Affleck-Dine mechanism of baryogenesis. This mechanism requires large squark or slepton expectation values to develop along flat directions in the early universe. This is generally not the case if the induced mass squared is positive, but does occur if it is negative. The resulting baryon to entropy ratio depends mainly on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction, and the reheat temperature after inflation. Unlike the original scenario, it is possible to obtain an acceptable baryon asymmetry without subsequent entropy releases.

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arXiv1994

Electroweak Baryogenesis: A Status Report

There are many reasons to believe that there might be new sources of CP-violation beyond the phases of the KM matrix. One of these is the possibility of electroweak baryogenesis. We describe some recent developments in this subject and make some comments on the possibility that the minimal standard model might itself be the origin of the baryon asymmetry. To appear in the Proceedings of the Third KEK Topical Conference on CP Violation, its Implications to Particle Physics and Cosmology, 16--18 November, 1993.

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arXiv1994

Electroweak Baryogenesis in the Adiabatic Limit

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 beyond that usually assumed is found. This arises because the generation of an asymmetry requires violation of approximately conserved currents by Higgs expectation values, which are small near the front of the walls. As applications, the asymmetries in multi-Higgs models and the minimal supersymmetric standard model are estimated to be proportional to $α_w^8$ and $α_w^6$ respectively. Also, in this limit the baryon asymmetry in the Minimal Standard Model is extraordinarily small.

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arXiv1993

Particle Astrophysics from the Particle Perspective

In this talk I discuss several topics at the interface of particle physics and astrophysics/cosmology. These include the problem of dark matter and two popular dark matter candidates: axions and neutralinos. I also discuss briefly some recent developments in electroweak baryogenesis, as well as a variety of somewhat more exotic topics: the fate of domain walls, axinos, non-vanishing cosmological constant, and cosmological constraints on models with dynamical supersymmetry breaking. Most of the material is review, however a few of the remarks, especially regarding axion cosmology in the framework of supersymmetry, I believe to be original.

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arXiv1993

Detecting Technibaryon Dark Matter

The technibaryon constitutes 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 the most important interaction is the charge radius. The scattering rates are typically of order $10^{-4}$ (kg keV day)$^{-1}$ for a technicolor scale of 1 TeV. For fermionic technibaryons the most important interaction is the magnetic dipole moment. The scattering rates in this case are considerably larger, typically between $10^{-1}$ and 1 (kg keV day)$^{-1}$, depending on the detector material. Rates this large may be detectable in the next generation of nuclear recoil experiments. Such experiments will also be sensitive to quite small technibaryon electric dipole moments.

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arXiv1993

Topics in String Phenomenology

We consider two questions in string ``phenomenology.'' First, are there any generic string predictions? Second, are there any general lessons which string theory suggests for thinking about low energy models, particularly in the framework of supersymmetry? Among the topics we consider are the squark and slepton spectrum, flavor symmetries, discrete symmetries including $CP$, and Peccei-Quinn symmetries. We also note that in some cases, discrete symmetries can be used to constrain the form of supersymmetry breaking.

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arXiv1993

Some Questions of Flavor in Supersymmetry

We consider certain naturalness questions in supersymmetric theories. Various suggestions which give rise to squark degeneracies are reviewed. A stringy scenario, discussed by Kaplunovsky and Louis, is the only one which leads to complete degeneracy of squarks and sleptons at the high scale. Alternatives include the possible existence of a gauged non-Abelian horizontal symmetry, broken at some scale, and theories in which the ``messengers" of supersymmetry breaking are gauge interactions. A model of the latter type is described, in which supersymmetry is {\it dynamically} broken at TeV energies. Models of this type can solve many of the naturalness problems of supersymmetric theories, and predict a rich phenomenology at SSC energies.

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arXiv1993

Dynamical Supersymmetry Breaking at Low Energies

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 breaking, which can explain the hierarchy, has been known for some time, but efforts to build such models have suffered from unwanted axions and difficulties with asymptotic freedom. In this paper, we describe an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and give a realistic example.

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arXiv1992

Some Two-Loop Corrections to the Finite Temperature Effective Potential in the Electroweak Theory

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 $ϕ$, the Higgs expectation value. Because the Higgs field is now known not to be extremely light, it is necessary to determine whether perturbation theory is a reliable guide to properties of the weak phase transition. In this note, we evaluate the most singular contributions to the potential at two loops as well as the leading strong interaction contributions. Above the critical temperature, the strong interaction corrections are reasonably small, while the weak corrections are about 10\%, even for rather small values of the Higgs field. At the critical temperature, the weak corrections have a more substantial effect, rendering the transition significantly more first order, but not significantly changing the upper bound on the Higgs mass required for baryogenesis.

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arXiv1992

String Theory: Lessons for Low Energy Physics

This talk considers possible lessons of string theory for low energy physics. These are of two types. First, assuming that string theory is the correct underlying theory of all interactions, we ask whether there are any generic predictions the theory makes, and we compare the predictions of string theory with those of conventional grand unified theories. Second, string theory offers some possible answers to a number of troubling naturalness questions. These include problems of discrete and continuous symmetries in general, and CP and the strong CP problem in particular.

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arXiv1992

Problems of Naturalness: Some Lessons from String Theory

We consider some questions of naturalness which arise when one considers conventional field theories in the presence of gravitation: the problem of global symmetries, the strong CP problem, and the cosmological constant problem. Using string theory as a model, we argue that it is reasonable to postulate weakly broken global discrete symmetries. We review the arguments that gravity is likely to spoil the Peccei-Quinn solution of the strong CP problem, and update earlier analyses showing that discrete symmetries can lead to axions with suitable properties. Even if there are not suitable axions, we note that string theory is a theory in which CP is spontaneously broken and $θ$ in principle calculable. $θ$ thus might turn out to be small along lines suggested some time ago by Nelson and by Barr.

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arXiv1992

Electroweak Baryogenesis: An Overview (Where are We Now?)

It now seems plausible that the observed baryon asymmetry may have been produced at the electroweak phase transition. We review the considerations which lead to this conclusion, focusing on the obstacles to making reliable estimates. These arise from incomplete knowledge of baryon-violating rates near the phase transition, our limited understanding of the phase transition itself, and incomplete understanding of the mechanisms which actually lead to an asymmetry.

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