119213450
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor RAA for neutral π 0 production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies E ≫ T . These results are important for the understanding of jet quenching in Au+Au collisions at 200 AGeV at RHIC. Comparison with data is performed applying the energy loss calculation to a relativistic ideal (3+1)-dimensional hydrodynamic description of the thermalized medium formed at RHIC.
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.
10799212
Classical field dynamics of the electroweak phase transition
We investigate the thermodynamics and dynamics of the electroweak phase transition by modeling the infrared physics with classical Yang-Mills Higgs theory. We discuss the accuracy of this approach and conclude that, for quantities whose determination is dominated by the infrared, the classical method should be correct up to parametrically suppressed [i.e., O({alpha})] corrections. For a Higgs self-coupling which at the tree level corresponds to m{sub H}{approx_equal}50 GeV, we determine the jump in the order parameter to be {delta}{phi}=1.5gT, the surface tension to be {sigma}=0.07g{sup 4}T{sup 3}, and the friction coefficient on the moving bubble wall due to infrared bosons to be {eta}{equivalent_to}P/v{sub w}=0.03{plus_minus}0.004g{sup 6}T{sup 4}. We also investigate the response of the Chern-Simons number to a spatially uniform chemical potential and find that it falls off a short distance inside the bubble wall, both in equilibrium and below the equilibrium temperature. {copyright} {ital 1997} {ital The American Physical Society}
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.
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.
18843095
Classical sphaleron rate on fine lattices
We measure the sphaleron rate for hot, classical Yang-Mills theory on the lattice, in order to study its dependence on lattice spacing. By using a topological definition of Chern-Simons number and going to extremely fine lattices [up to $\ensuremath{\beta}=32,$ or lattice spacing ${a=1/(8g}^{2}T)]$ we demonstrate nontrivial scaling. The topological susceptibility, converted to physical units, falls with lattice spacing on fine lattices in a way which is consistent with linear dependence on a (the Arnold-Son-Yaffe scaling relation) and is difficult to reconcile with a nonzero continuum limit. We also explain some unusual behavior of the rate in small volumes, reported by Ambj\o{}rn and Krasnitz.
17230629
Threshold corrections in K3 × T2 heterotic string compactifications
Abstract We consider compactifications of the heterotic string on K 3 × T 2 so that the resulting theory in d = 4 space-time dimensions has N = 2 supersymmetry. The gravitational and gauge coupling constants of the low-energy effective theory receive threshold corrections from loops of superheavy string states. We calculate these corrections for the case when the K 3 surface is a Z n orbifold of a four-torus T 4. The results are used to determine the one-loop prepotential F 0 (1) for the vector multiplets and the gravitational coupling F 1 (1) .
15744838
Instabilities in heterotic M-theory induced by open membrane instantons
Abstract We study the effective low energy supergravity of the strongly coupled heterotic string compactified on a Calabi–Yau 3-fold with generic E 8 × E 8 gauge bundle. We focus on the effective potential for the chiral scalars. The effective superpotential can be studied using the dual 11-dimensional M-theory background involving insertions of M5-branes along an interval. In such backgrounds, in some regions of moduli space, the leading nonperturbative contributions are due to open membrane instantons. These instantons lead to both attractive and repulsive forces between the 5-branes and the orientifold “M9-branes”, depending on the region of moduli space. The resulting dynamics on moduli space include a strong coupling dual to the Dine–Seiberg instability, in which the interval grows. We discuss conditions under which the 5-branes are attracted to the wall and comment on the relevance of these results to the study of chirality-changing phase transitions in heterotic M-theory.
768594
Calabi–Yau Black Holes and (0,4) Sigma Models
Abstract:When an M-theory fivebrane wraps a holomorphic surface ? in a Calabi–Yau 3-fold X the low energy dynamics is that of a black string in 5 dimensional ? =1 supergravity. The infrared dynamics on the string worldsheet is an ? = (0,4) 2D conformal field theory. Assuming the 2D CFT can be described as a nonlinear sigma model, we describe the target space geometry of this model in terms of the data of X and ?. Variations of weight two Hodge structures enter the construction of the model in an interesting way.
117503787
Geometrical Aspects of Anomalies
55883682
Crossing the wall: branes versus bundles
We test a recently proposed wall-crossing formula for the change of the Hilbert space of Bogomol’nyi–Prasad–Sommerfield (BPS) states in d = 4, N = 2 theories. We study decays of D4D2D0 systems into pairs of D4D2D0 systems and we show how the wall-crossing formula reproduces results of Göttsche and Yoshioka on wall-crossing behavior of the moduli of slope-stable holomorphic bundles over holomorphic surfaces. Our comparison shows very clearly that the moduli space of the D4D2D0 system on a rigid surface in a Calabi–Yau is not the same as the moduli space of torsion-free sheaves, even when worldhseet instantons are neglected. Moreover, we argue that the physical formula should make some new mathematical predictions for a future theory of the moduli of stable objects in the derived category.