7373896
Five-brane instantons and R**2 couplings in N=4 string theory
We compute the gravitational coupling F{sub 1} for type IIA string theory on K3{times}T{sup 2} and use string-string duality to deduce the corresponding term for heterotic string on T{sup 6}. The latter is an infinite sum of gravitational instanton effects which we associate with the effects of Euclidean five-branes wrapped on T{sup 6}. These five-branes are the neutral five-branes or zero-size instantons of heterotic string theory. {copyright} {ital 1998} {ital The American Physical Society}
15868022
Donaldson Invariants for Non-Simply Connected Manifolds
Abstract:We study Coulomb branch (“u-plane”) integrals for supersymmetric SU(2),SO(3) Yang–Mills theory on 4-manifolds X of b1(X)>0, b2+(X)= 1. Using wall-crossing arguments we derive expressions for the Donaldson invariants for manifolds with b1(X)>0, b2+(X)>0. Explicit expressions for , where Fg is a Riemann surface of genus g are obtained using Kronecker's double series identity. The result might be useful in future studies of quantum cohomology.
118337669
Symmetries of the Bosonic String S-Matrix
The bracket operation on mutually local BRST classes may be combined with Lorentz invariance and analyticity to write an infinite set of finite difference relations on string scattering amplitudes. When combined with some simple physical criteria these relations uniquely determine the genus zero string $S$-matrix for $N\leq 26$-particle scattering in $\IR^{25,1}$ in terms of a single parameter, $\kappa$, the string coupling. We propose that the high-energy limit of the relations are the Ward identities for the high-energy symmetries of string theory.
122595912
Anomalies in Nonlinear $\sigma$ Models
Certain nonlinear sigma models with fermions suffer from an anomaly similar to the one in non-Abelian gauge theory. We exhibit this anomaly using both perturbative and global methods. The affected theories are ill defined and hence unsuitable for describing low-energy dynamics. They include certain supersymmetric models in four space-time dimensions.
124306496
The M theory three form and E(8) gauge theory
14205277
Melvin Models and Diophantine Approximation
Melvin models with irrational twist parameter provide an interesting example of conformal field theories with non-compact target space, and localized states which are arbitrarily close to being delocalized. We study the torus partition sum of these models, focusing on the properties of the regularized dimension of the space of localized states. We show that its behavior is related to interesting arithmetic properties of the twist parameter γ, such as the Lyapunov exponent. Moreover, for γ in a set of measure one the regularized dimension is in fact not a well-defined number but must be considered as a random variable in a probability distribution.
5758194
Constraining the New Aether: gravitational Cherenkov radiation
We study the simplest concrete theory for spontaneous Lorentz violation, the ``New Aether theory'' of Jacobson and Mattingly, which is a vector-tensor gravitational theory with a fixed-modulus condition on the vector field. We show that the observation of ultra-high energy cosmic rays (which implies the absence of energy loss via various Cherenkov type processes) places constraints on the parameters of this theory, which are much stronger than those previously found in the literature and are also stronger than the constraints generically arising when gravity displays sub-luminal propagation.
118922289
Shear Viscosity in Weakly Coupled N=4 Super Yang-Mills Theory Compared to QCD
We compute the shear viscosity of weakly coupled N=4 supersymmetric Yang-Mills theory. Our result for {eta}/s, the viscosity to entropy-density ratio, is many times smaller than the corresponding weak-coupling result in QCD. This suggests that {eta}/s of QCD near the transition point is several times larger than the viscosity bound, {eta}/s{>=}1/4{pi}.
119279378
Bjorken flow, plasma instabilities, and thermalization
A bstractAt asymptotically high energies, thermalization in heavy ion collisions can be described via weak-coupling QCD. We present a complete treatment of how thermalization proceeds, at the parametric weak-coupling level. We show that plasma instabilities dominate the dynamics, from immediately after the collision until well after the plasma becomes nearly in equilibrium. Initially they drive the system close to isotropy, but Bjorken expansion and increasing diluteness makes the system again become more anisotropic. At time $ \tau \sim {\alpha^{{\frac{{ - 12}}{5}}}}Q_s^{{ - 1}} $ the dynamics become dominated by a nearly-thermal bath; and at time $ \tau \sim {\alpha^{{\frac{{ - 5}}{2}}}}Q_s^{{ - 1}} $ the bath comes to dominate the energy density, completing thermalization. After this time there is a nearly isotropic and thermal Quark-Gluon Plasma.
119468202
The nonperturbative broken phase sphaleron rate
Abstract I present a technique for measuring the broken phase sphaleron rate nonperturbatively. There are three parts to the calculation: determination of the probability distribution of Chern-Simons number N CS ; measurement of 〈| dN CS / dt |〉 N CS = 1 2 , the mean rate of change of N CS at the barrier; and measurement of the “dynamical prefactor,” the fraction of barrier crossings which result in a permanent integer change in N CS .
119555468
Next-to-Leading Order Shear Viscosity in lambda phi**4 Theory
We show that the shear viscosity of $\ensuremath{\lambda}{\ensuremath{\phi}}^{4}$ theory is sensitive at next-to-leading order to soft physics, which gives rise to subleading corrections suppressed by only a half power of the coupling, $\ensuremath{\eta}=\phantom{\rule{0ex}{0ex}}\frac{(3033.54+1548.3\sqrt{(N+2)\ensuremath{\lambda}/72})N{T}^{3}}{\frac{N+2}{3}{\ensuremath{\lambda}}^{2}}$. The series appears to converge about as well as the series for the pressure.