118416779
Next-to-leading order thermal photon production in a weakly coupled quark-gluon plasma
A bstractWe compute the next-to-leading order O(g) correction to the thermal photon production rate in a QCD plasma. The NLO contributions can be expressed in terms of gauge invariant condensates on the light cone, which are amenable to novel sum rules and Euclidean techniques. We expect these technologies to be generalizable to other NLO calculations. For the phenomenologically interesting value of αs = 0.3, the NLO correction represents a 20% increase and has a functional form similar to the LO result.
12239452
Lower bound on the propagation speed of gravity from gravitational Cherenkov radiation
Recently, interesting 4-D Lorentz violating models have been proposed, in which all particles have a common maximum velocity c, but gravity propagates (in the preferred frame) with a different maximum velocity cg≠c. We show that the case cg < c is very tightly constrained by the observation of the highest energy cosmic rays. Assuming a galactic origin for the cosmic rays gives a conservative bound of c−cg <2 × 10−15c; if the cosmic rays have an extragalactic origin the bound is orders of magnitude tighter, of order c−cg < 2 × 10−19c.
119023526
The phantom menaced: Constraints on low-energy effective ghosts
It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum. We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff $\ensuremath{\Lambda}$ which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels. Assuming only that ghosts interact at least gravitationally, we show that $\ensuremath{\Lambda}\ensuremath{\lesssim}3\mathrm{MeV}$ for consistency with the cosmic gamma ray background. We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded.
119020278
Energy loss of leading partons in a thermal QCD medium
We consider bremsstrahlung energy loss for hard partons traversing a quark-gluon plasma (QCP). Accounting correctly for the probabilistic nature of the energy loss, and making a leading-order-accurate treatment of bremsstrahlung, we find that the suppression of the spectrum is nearly flat, with the most suppression at energies $E~30\phantom{\rule{0.3em}{0ex}}T$ (where T is the QGP temperature), without the need for initial state effects such as shadowing and the Cronin effect. This flat pattern should also be observed at the LHC (Large Hadron Collider) out to an energy of $~30\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$.
118805589
Second order hydrodynamic coefficients from kinetic theory
In a relativistic setting, hydrodynamic calculations which include shear viscosity (which is first order in an expansion in gradients of the flow velocity) are unstable and acausal unless they also include terms to second order in gradients. To date such terms have only been computed in supersymmetric N=4 super-Yang-Mills theory at infinite coupling. Here we compute these second-order hydrodynamic coefficients in weakly coupled QCD, perturbatively to leading order in the QCD coupling, using kinetic theory. We also compute them in QED and scalar {lambda}{phi}{sup 4} theory.
16445189
Chern-Simons number diffusion and hard thermal loops on the lattice
We develop a discrete lattice implementation of the hard thermal loop effective action by the method of added auxiliary fields. We use the resulting model to measure the sphaleron rate (topological susceptibility) of Yang-Mills theory at weak coupling. Our results give parametric behavior in accord with the arguments of Arnold, Son, and Yaffe, and are in quantitative agreement with the results of Moors, Hu, and Muller.
13804747
Three-manifold topology and the Donaldson-Witten partition function
Abstract We consider Donaldson-Witten theory on four-manifolds of the form X = Y × S 1 where Y is a compact three-manifold. We show that there are interesting relations between the four-dimensional Donaldson invariants of X and certain topological invariants of Y. In particular, we reinterpret a result of Meng-Taubes relating the Seiberg-Witten invariants to Reidemeister-Milnor torsion. If b1(Y) > 1 we show that the partition function reduces to the Casson-Walker-Lescop invariant of Y, as expected on formal grounds. In the case b1(Y) = 1 there is a correction. Consequently, in the case b1(Y) = 1, we observe an interesting subtlety in the standard expectations of Kaluza-Klein theory when applied to supersymmetric gauge theory compactified on a circle of small radius.
120400824
Rationality in conformal field theory
We show that if the one-loop partition function of a modular invariant conformal field theory can be expressed as a finite sum of holomorphically factorized terms thenc and all values ofh are rational.
11977234
Ample D4-D2-D0 Decay
We study the wall-crossing behavior of the index of BPS states for D4-D2-D0 brane systems on a Calabi-Yau 3-fold at large radius and point out that not only is the ``BPS index at large radius'' chamber-dependent, but that the changes in the index can be large in the sense that they dominate single-centered black hole entropy. We discuss implications for the weak coupling OSV conjecture. We also analyze the near horizon limit of multicentered solutions, introduced in arXiv:0802.2257, for these particular configurations and comment on a general criterion, conjectured in arXiv:0802.2257, which identifies those multicentered solutions whose near horizon limit corresponds to a geometry with a single asymptotic AdS_3 x S^2 boundary.
15061850
Profiling the brane drain in a nonsupersymmetric orbifold
We study D-branes in a nonsupersymmetric orbifold of type 2/Γ, perturbed by a tachyon condensate, using a gauged linear sigma model. The RG flow has both Higgs and Coulomb branches, and each branch supports different branes. The Coulomb branch branes account for the ``brane drain'' from the Higgs branch, but their precise relation to fractional branes has hitherto been unknown. Building on the results of hep-th/0403016 we construct, in detail, the map between fractional branes and the Coulomb/Higgs branch branes for two examples in the type 0 theory. This map depends on the phase of the tachyon condensate in a surprising and intricate way. In the mirror Landau-Ginzburg picture the dependence on the tachyon phase is manifested by discontinuous changes in the shape of the D-brane.
122690514
Strings in the Operator Formalism
Abstract We consider string theories in the operator formalism. In particular we develop Polyakov strings completely in the operator language. The operator approach turns out to be economical, self-contained and manifestly modular invariant.