Michael E. Peskin

Transmission of supersymmetry breaking from a four-dimensional boundary

In the strong-coupling limit of the heterotic string theory constructed by Ho{hacek r}ava and Witten, an 11-dimensional supergravity theory is coupled to matter multiplets confined to 10-dimensional mirror planes. This structure suggests that realistic unification models are obtained, after compactification of 6 dimensions, as theories of 5-dimensional supergravity in an interval, coupling to matter fields on 4-dimensional walls. Supersymmetry breaking may be communicated from one boundary to another by the 5-dimensional fields. In this paper, we study a toy model of this communication in which 5-dimensional super-Yang-Mills theory in the bulk couples to chiral multiplets on the walls. Using the auxiliary fields of the Yang-Mills multiplet, we find a simple algorithm for coupling the bulk and boundary fields. We demonstrate two different mechanisms for generating soft supersymmetry breaking terms in the boundary theory. We also compute the Casimir energy generated by supersymmetry breaking. {copyright} {ital 1998} {ital The American Physical Society}

The alignment of the vacuum in theories of technicolor

We study a class of models of dynamical weak-interaction symmetry breaking suggested by the work of Weinberg and Susskind. We demonstrate in these models some simple relations which determine the alignment of weakly gauged subgroups and the masses of pseudo-Goldstone bosons. We illustrate these methods by computing the spectrum of pseudo-Goldstone bosons in three models recently examined by Dimopoulos. These models are seen to contain a very light charged Higgs boson, whose mass we estimate by the use of chiral perturbation theory. In one of these models, we observe that the energetically preferred vacuum is a phenomenologically unpleasant one.

String field theory on the conformal plane (I).: Kinematical Principles

We formulate string field theory geometrically by writing each term in the field theory action. as an expectation value in the 2-dimensional conformal field theory on the world surface. We show how the symmetries of the theory can be analyzed and the gauge invariance demonstrated from this point of view. As an application, we give a complete proof of the gauge invariance of Wittens open string field theory.

Collider signatures of new large space dimensions

Recently, Arkani-Hamed, Dimopoulos, and Dvali have proposed that there are extra compact dimensions of space, accessible to gravity but not to ordinary matter, which could be macroscopically large. In this letter, we argue that high-energy collider processes in which gravitons are radiated into these new dimensions place significant, model-independent constraints on this picture. We present the constraints from anomalous single photon production at e{sup +}e{sup {minus}} colliders and from monojet production at hadron colliders.

Short Distance Analysis for Heavy Quark Systems. 1. Diagrammatics

Abstract We investigate the sense in which the coupling of soft external probes to heavy quark-antiquark bound states may be considered a short-distance process. We apply an observation of Applequist, Dine and Muzinich to justify performing operator product expansions on gluon insertions in the heavy-quark state; this allows us to summarize the couplings of this state to external probes as the matrix elements of a series in local operators. The criterion for the validity of the expansion, for a bound state of size a0, is that the external momentum scale be much less than the Rydberg energy g2/a0 associated with the color Coulomb potential. We calculate the Wilson coefficients of our expansion to leading order in g2 both for static quarks and for non-relativistic Q Q bound states.

TeV strings and collider probes of large extra dimensions

Arkani-Hamed, Dimopoulos, and Dvali have proposed that the fundamental gravitational scale is close to 1 TeV, and that the observed weakness of gravity at long distances is explained by the presence of large extra compact dimensions. If this scenario is realized in a string theory of quantum gravity, the string excited states of standard model particles will also have TeV masses. These states will be visible to experiment and in fact provide the first signatures of the presence of a low quantum gravity scale. Their presence also affects the more familiar signatures due to real and virtual graviton emission. We study the effects of these states in a simple string model. (c) 2000 The American Physical Society.

Gauge invariance of string fields

Abstract We identify the gauge invariances of the linearized field theory of strings which give rise to the Yang-Mills and general coordinate invariance of this theory. We construct a kinetic energy term for string fields which is invariant to these gauge symmetries. By gauge-fixing, we derive from this action the expressions for the free string action, in particular gauges found by Kaku and Kikkawa and by Siegel. The structure of Stueckelberg auxilliary fields required to make the gauge-invariant action local is rather intricate; to clarify this structure, we develop a theory of differential forms on the space of strings. We conclude with some remarks on the origin of the dilaton and the appearance in the superstring of local supersymmetry.

Difficulties for the Evolution of Pure States Into Mixed States

Motivated by Hawkings proposal that the quantum-mechanical density matrix ϱ obeys an equation more general than the Schrodinger equation, we study the general properties of evolution equations for ϱ. We argue that any more general equation for ϱ violates either locality or energy-momentum conservation.

N=2 Superconformal Symmetry and SO(2,1) Current Algebra

Abstract We demonstrate that all unitary representations of the N =2 superconformal algebra (for c >3) may be obtained from representations of SO(2,1) current algebra by subtracting and then adding back a free boson. This construction gives insight into the unitary domains for N =2 representations. It may also have a deeper structural significance.

Short-distance analysis for heavy-quark systems: (II). Applications

Abstract We apply the methodology of the operator product expansion to a number of processes involving the coupling of heavy quark-anti-quark mesons to light hadrons. Our methods apply to on-shell scattering processes and transitions, but they are strictly valid only when the quark masses are very heavy (of order 25 GeV). In this regime, however, we derive color gauge theory predictions for heavy meson-proton total cross sections, exclusive photoproduction, and Zweig-forbidden hadronic transitions; these heavy-quark computations are then used to estimate the corresponding quantities in the ϕ and Y systems. We discuss also the long-range interaction between two heavy-quark mesons.