arXiv subjects

Michael Dine

Publications and source records attributed to Michael Dine.

At least 91 records · Page 5Linked to original sources

arXiv2002

Brane World Susy Breaking from String/M Theory

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--brane non-derivative contact interactions coupling the visible and hidden sectors and is not of the no-scale sequestered form. This leads to non-universal scalar masses and without additional assumptions about flavor symmetries may in general induce dangerous sflavor violation even though the Standard Model and supersymmetry branes are physically separated. Deviations from the sequestered form are dictated by bulk supersymmetry and can in most cases be understood as arising from exchange of bulk supergravity fields between branes or warping of the internal geometry. Unacceptable visible sector tree-level tachyons arise in many models but may be avoided in certain classes of compactifications. Anomaly mediated and gaugino mediated contributions to scalar masses are sub-dominant except in special circumstances such as a flat or AdS pure five--dimensional bulk geometry without bulk vector multiplets.

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arXiv2001

Comments on Non-Commutative Phenomenology

It is natural to ask whether non-commutative 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.

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arXiv2001

Brane World Susy Breaking

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 and warping of the internal geometry. This is contrary to the notion that bulk locality gives rise to a sequestered no-scale form of the Kahler potential with vanishing tree-level masses and solves the supersymmetric flavor problem. As a result, a radiatively generated anomaly mediated superpartner spectrum is not a generic outcome of these theories.

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arXiv2001

Slepton Flavor Physics at Linear Colliders

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 understand the absence of low energy quark and lepton flavor changing neutral currents are surveyed and many are found to predict observable slepton flavor violating signals at linear colliders. The observation or absence of such sflavor violation will thus provide important indirect clues to very high energy physics. Previous analyses of slepton flavor oscillations are also extended to include the effects of finite width and mass differences.

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arXiv2001

Some Issues in Flat Direction Baryogenesis

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. We also consider the decay of the condensate, and possible implications of these observations for the formation of Q-balls.

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arXiv2001

Dark Energy in Perturbative String Cosmology

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 potentials for the moduli. The solutions of the Fischler-Susskind equations all have Big Bang or Big Crunch Singularities. We believe that an S-matrix (or S-vector) exists in this context but cannot be calculated by purely perturbative methods. We study the possibility of metastable de Sitter vacua in such weakly coupled scenarios, and conclude that the S-matrix of the extreme weak coupling region cannot probe de Sitter physics. We also consider proposed explanations of the dark energy from the perspective of string theory, and find that most are implausible. We note that it is possible that the axion constitutes both the dark matter and the dark energy.

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arXiv2001

String Theory, Large Dimensions and Supersymmetry

With our current level of understanding, the problem of making string theory predictions is not one of "solving" the theory, but rather of trying to determine whether there are any generic expectations. Within this context, we discuss what it would mean to predict low energy supersymmetry, and consider questions like: what is the form of low energy CP violation, is unification a string prediction, and others.

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arXiv2001

Dark Matter and Dark Energy: A Physicist's Perspective

For physicists, recent developments in astrophysics and cosmology present exciting challenges. We are conducting "experiments" in energy regimes some of which will be probed by accelerators in the near future, and others which are inevitably the subject of more speculative theoretical investigations. Dark matter is an area where we have hope of making discoveries both with accelerator experiments and dedicated searches. Inflation and dark energy lie in regimes where presently our only hope for a fundamental understanding lies in string theory.

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arXiv2001

CP Violation and the Scale of Supersymmetry Breaking

Supersymmetric models with a high supersymmetry breaking scale give, in general, large contributions to epsilon_K 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 two generation sfermions, anomaly mediation and gaugino mediation. There is then strong motivation for `approximate CP', that is a situation where all CP violating phases are small. In contrast, in supersymmetric models with a low breaking scale it is quite plausible that the CKM matrix is the only source of flavor and CP violation. Gauge mediation provides a concrete example. Approximate CP is then unacceptable. Upcoming measurements of the CP asymmetry in B to ψK_S might exclude or support the idea of approximate CP and consequently probe the scale of supersymmetry breaking.

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arXiv2000

TASI Lectures on The Strong CP Problem

These lectures discuss the $θ$ parameter of QCD. After an introduction to anomalies in four and two dimensions, the parameter is introduced. That such topological parameters can have physical effects is illustrated with two dimensional models, and then explained in QCD using instantons and current algebra. Possible solutions including axions, a massless up quark, and spontaneous CP violation are discussed.

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arXiv2000

Remarks on the Racetrack Scheme

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 note, we explore this scenario. We find that quite generally, some number of discrete tunings are required in order that the mechanism yield a small gauge coupling. Even then, there is no sense in which a weak coupling approximation is valid. On the other hand, certain holomorphic quantities can be computed, so such a scheme is in principle predictive. Searching for models which realize this mechanism is thus of great interest. We also remark on cosmology in these schemes.

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arXiv2000

The Utility of Quantum Field Theory

This talk surveys a broad range of applications of quantum field theory, as well as some recent developments. The stress is on the notion of effective field theories. Topics include implications of neutrino mass and a possible small value of $\sin(2β)$, supersymmetric extensions of the standard model, the use of field theory to understand fundamental issues in string theory (the problem of multiple ground states and the question: does string theory predict low energy supersymmetry), and the use of string theory to solve problems in field theory. Also considered are a new type of field theory, and indications from black hole physics and the cosmological constant problem that effective field theories may not completely describe theories of gravity.

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arXiv2000

On Anthropic Solutions of the Cosmological Constant Problem

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 first is a version of the BP model with precisely two large dimensions. The second involves 6-branes and antibranes wrapped on supersymmetric 3-cycles of Calabi-Yau manifolds, and the third is a version of the irrational axion model. All of them have possible problems in explaining the size of microwave background fluctuations. We also find that most models of this type predict that all constants in the low energy Lagrangian, as well as the gauge groups and representation content, are chosen from an ensemble and cannot be uniquely determined from the fundamental theory. In our opinion, this significantly reduces the appeal of this kind of solution of the cosmological constant problem. On the other hand, we argue that the vacuum selection problem of string theory might plausibly have an anthropic, cosmological solution.

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arXiv2000

TASI Lectures on M Theory Phenomenology

These lectures discuss some of the general issues in developing a phenomenology for Superstring Theory/M Theory. The focus is on the question: how might one obtain robust, generic predictions. For example, does the theory predict low energy supersymmetry breaking? In the course of these explorations, basics of supersymmetry and supersymmetry breaking, string moduli, cosmological issues, and other questions are addressed. The notion of approximate moduli and their possible role plays a central role in the discussion.

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arXiv2000

Towards a Solution of the Moduli Problems of String Cosmology

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 dilaton sit at points of enhanced symmetry. The dilaton has a potential similar to those of racetrack models; it is very massive and its dynamics do not break supersymmetry. The dilaton is able to find the minimum of its potential because the energy is dominated by non-zero momentum modes. This energy need not be thermal. The effective potential for the dilaton is quite different from its flat space form. If certain conditions are satisfied, the dilaton settles into the desired minimum; if not, it is forced to weak coupling.

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arXiv2000

Some Reflections on Moduli, Their Stabilization and Cosmology

We review some aspects of moduli in string theory. We argue that one should focus on {\it approximate moduli spaces}, and that there is evidence that such spaces exist non-perturbatively. We ask what it would mean for string theory to predict low energy supersymmetry. Aspects of two proposed mechanisms for fixing the moduli are discussed, and solutions to certain cosmological problems associated with moduli are proposed.

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arXiv1999

Non-Renormalization Theorems for Operators with Arbitrary Numbers of Derivatives in ${\cal N}=4$ Yang Mills Theory

We generalize the proof of the non-renormalization of the four derivative operators in ${\cal N}=4$ Yang Mills theory with gauge group SU(2) to show that certain terms with 2N derivatives are not renormalized in the theory with gauge group SU(N). These terms may be determined exactly by a simple perturbative computation. Similar results hold for finite ${\cal N}=2$ theories. We comment on the implications of these results.

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arXiv1999

Possible Scales of New Physics

The biggest question in beyond the standard model physics is what are the scales of new physics. Ideas about scales, as well as experimental evidence and constraints, are surveyed for a variety of possible forms of new physics: supersymmetry, neutrino masses, unification, and superstring theory.

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