Scott A. Yost

Open Strings in Background Gauge Fields

Some properties of open bosonic strings in a background abelian gauge field are investigated. We derive the equations of motion and effective action for the electromagnetic field, and discuss the effect of the field on the string spectrum and partition function.

Loop corrections to superstring equations of motion

Abstract We extend to the O(32) superstring our program of renormalizing string theory by cancelling BRST anomalies between different genus worldsheets. We calculate all the anomalies arising to lowest nontrivial loop order and in general background fields. At tree level, string consistency requires the background fields to satisfy equations of motion which ensure the conformal invariance of the underlying sigma model. We implement loop anomaly cancellation by adding to these equations appropriate loop-order source terms which necessarily break conformal invariance. The procedure leads to consistent loop-corrected equations of motion which can be derived from a spacetime effective action. The loop-order terms in this action incorporate a number of crucial aspects of spacetime physics, including the interaction of the photon with the graviton and the interactions of the antisymmetric tensor field with the gauge field which are responsible for spacetime gauge anomaly cancellation. We take these results as compelling evidence that loop-corrected string theory is associated with sigma models which are not conformally invariant in the usual sense. An extended version of conformal invariance, whose deep structure has yet to be uncovered, presumably incorporates string loop physics.

Adding Holes and Crosscaps to the Superstring

A hole or crosscap in the world sheet of a superstring creates the eigenstate of the quantized boundary conditions. This observation makes the calculation of open string loop divergences almost trivial. We confirm that the O(32) theory is finite. In other theories, the divergences induce BRST anomalies. Cancelling them against the tree-level BRST anomalies of the sigma model gives the loop-corrected equations of motion without ambiguities.

String Loop Corrections to beta Functions

Abstract We study the problem of finding the beta functions, and the associated spacetime effective action, for interacting open and closed strings propagating in background fields. String loop divergences play a crucial role in this problem. Cancelling them against sigma model divergences gives a consistent set of loop-corrected beta functions, which can be derived from a simple generalization of the string-tree-level effective action. This suggests the existence of new string theories which are conformally invariant only after all world sheets have been summed.

Superstring field theory

We construct a class of cubic gauge-invariant actions for superstring field theory, gauge fix one of them and show that it reproduces the known superstring S-matrix. In our construction boson string fields are taken in the 0 picture and fermion string fields in the −12 picture. For 0 picture the bosonic kinetic term requires an insertion carrying −2 units of picture number. We construct all possible picture-changing operators with the required properties. We use the simplest of these to construct the superstring action we choose to analyze here. In the gauge b1 + b−1 = 0, the conformal mappings needed to evaluate the tree diagrams are algebraic, and this enables a completely explicit derivation of the Koba-Nielsen amplitudes. In this gauge the action formally linearizes, a phenomenon familiar from other Chern-Simons type theories. Nontrivial scattering amplitudes are obtained by approaching this gauge as a limit.

Charged black holes in two-dimensional string theory

We discuss two dimensional string theories containing gauge fields, introduced either via coupling to open strings, in which case we get a Born-Infeld type action, or via heterotic compactification. The solutions of the modified background field equations are charged black holes which exhibit interesting space time geometries. We also compute their masses and charges.

All order ε-expansion of Gauss hypergeometric functions with integer and half/integer values of parameters

It is proved that the Laurent expansion of the following Gauss hypergeometric functions, 2F1 (I1 + aε, I2 + bε; I3 + cε; z) , 2F1 (I1 + aε, I2 + bε; I3 + 1 2 + cε; z) , 2F1 (I1 + 1 2 + aε, I2 + bε; I3 + cε; z) , 2F1 (I1 + 1 2 + aε, I2 + bε; I3 + 1 2 + cε; z) , 2F1 (I1 + 1 2 + aε, I2 + 1 2 + bε; I3 + 1 2 + cε; z) , where I1, I2, I3 are an arbitrary integer nonnegative numbers, a, b, c are an arbitrary numbers and ε is an arbitrary small parameters, are expressible in terms of the harmonic polylogarithms of Remiddi and Vermaseren with polynomial coefficients. An efficient algorithm for the calculation of the higher-order coefficients of Laurent expansion is constructed. Some particular cases of Gauss hypergeometric functions are also discussed.

Multiple (inverse) binomial sums of arbitrary weight and depth and the all-order ε-expansion of generalized hypergeometric functions with one half-integer value of parameter

We continue the study of the construction of analytical coefficients of the ?-expansion of hypergeometric functions and their connection with Feynman diagrams. In this paper, we show the following results: Theorem A: The multiple (inverse) binomial sums where k = ?1, Sa(j) is a harmonic series, Sa(j) = ?jk = 1?1/ka, and c is any integer number are expressible in terms of Remiddi-Vermaseren functions; Theorem B: The hypergeometric functions are expressible in terms of the harmonic polylogarithms of Remiddi and Vermaseren with coefficients that are ratios of polynomials.

New results on the theoretical precision of the LEP / SLC luminosity

A heat moldable composition which useful for preparing ceramic bodies comprises an inorganic material that sets as a result of baking or sintering, and a hydroxypropyl methylcellulose having a DS of at least 1.4 and an MS of at least 0.6, wherein DS is the degree of substitution of methoxyl groups and MS is the molar substitution of hydroxypropoxyl groups, and a viscosity of up to 80 mPa·s, determined as a 2% by weight solution in water at 20° C., wherein the heat moldable composition comprises at least 40 weight percent of the inorganic material and at least 10 weight percent of the hydroxypropyl methylcellulose, and wherein the composition does not comprise more than 5 weight percent of water, all percentages being based on the total weight of the composition.

On the all-order ε-expansion of generalized hypergeometric functions with integer values of parameters

We continue our study of the construction of analytical coefficients of the epsilon-expansion of hypergeometric functions and their connection with Feynman diagrams. In this paper, we apply the approach of obtaining iterated solutions to the differential equations associated with hypergeometric functions to prove the following result: Theorem 1. The epsilon-expansion of a generalized hypergeometric function with integer values of parameters, pFp−1(I1+a1e,...,Ip+ape;Ip+1+b1e,...,I2p−1+bp−1;z) , is expressible in terms of generalized polylogarithms with coefficients that are ratios of polynomials. The method used in this proof provides an efficient algorithm for calculating of the higher-order coefficients of Laurent expansion.