Gravitational Lorentz Violations from M-Theory

In an attempt to bridge the gap between M-theory and braneworld phenomenology, we present various gravitational Lorentz-violating braneworlds which arise from p-brane systems. Lorentz invariance is still preserved locally on the braneworld. For certain p-brane intersections, the massless graviton is quasi-localized. This also results from an M5-brane in a C-field. In the case of a p-brane perturbed from extremality, the quasi-localized graviton is massive. For a braneworld arising from global AdS_5, gravitons travel faster when further in the bulk, thereby apparently traversing distances faster than light.Comment: 13 pages, 1 figure, LaTeX, references added, minor corrections and addition

Absorption by Extremal D3-branes

The absorption in the extremal D3-brane background is studied for a class of massless fields whose linear perturbations leave the ten-dimensional background metric unperturbed, as well as the minimally-coupled massive scalar. We find that various fields have the same absorption probability as that of the dilaton-axion system, which is given exactly via the Mathieu equation. We analyze the features of the absorption cross-sections in terms of effective Schr\"odinger potentials, conjecture a general form of the dual effective potentials, and provide explicit numerical results for the whole energy range. As expected, all partial-wave absorption probabilities tend to zero (one) at low (large) energies, and exhibit an oscillatory pattern as a function of energy. The equivalence of absorption probabilities for various modes has implications for the correlation functions on the field, including subleading contributions on the field-theory side. In particular, certain half-integer and integer spin fields have identical absorption probabilities, thus providing evidence that the corresponding operator pairs on the field theory side belong to the same supermultiplets.Comment: Latex, 9 figures and 17 page

Strongly-Coupled Quarks and Colorful Black Holes

We use the AdS/CFT correspondence to study the behavior of strongly-coupled quarks in a black hole background. The supergravity background consists of a six-dimensional Schwarzschild-black string AdS soliton, for which the bulk horizon extends from the AdS boundary down to an infra-red floor. By going to higher energy scales, the regime of validity of the classical supergravity background can be extended closer to the singularity than might be expected from the four-dimensional perspective. Small black holes potentially created by the Large Hadron Collider could typically carry color charges inherited from their parton progenitors. The dynamics of quarks near such a black hole depends on the curved spacetime geometry as well as the strong interaction with the color-charged black hole. We study the resulting behavior of quarks and compute the rate at which a quark rotating around the black hole loses energy. We also investigate how the interaction between a quark and an antiquark is altered by the presence of the black hole, which results in a screening length.Comment: Proceedings of the DPF-2011 Conference, 8 pages, 5 figures, added reference

Open Wilson Lines and Chiral Condensates in Thermal Holographic QCD

We investigate various aspects of a proposal by Aharony and Kutasov arXiv:0803.3547 [hep-th] for the gravity dual of an open Wilson line in the Sakai-Sugimoto model or its non-compact version. In particular, we use their proposal to determine the effect of finite temperature, as well as background electric and magnetic fields, on the chiral symmetry breaking order parameter. We also generalize their prescription to more complicated worldsheets and identify the operators dual to such worldsheets.Comment: 45 pages, 18 figures; added reference

Massive-Scalar Absorption by Extremal p-branes

We study the absorption probability of minimally-coupled massive scalars by extremal p-branes. In particular, we find that the massive scalar wave equation under the self-dual string background has the same form as the massless scalar wave equation under the dyonic string background. Thus it can be cast into the form of a modified Mathieu equation and solved exactly. Another example that we can solve exactly is that of the D=4 two-charge black hole with equal charges, for which we obtain the closed-form absorption probability. We also obtain the leading-order absorption probabilities for D3-, M2- and M5-branes.Comment: Latex, 11 pages, reference adde

No-Drag String Configurations for Steadily Moving Quark-Antiquark Pairs in a Thermal Bath

We investigate the behavior of stationary string configurations on a five-dimensional AdS black hole background which correspond to quark-antiquark pairs steadily moving in an N=4 super Yang-Mills thermal bath. There are many branches of solutions, depending on the quark velocity and separation as well as on whether Euclidean or Lorentzian configurations are examined.Comment: references added; statements corrected; eliminated computation of jet quenching parameter from Wilson loop of [Liu, Rajagopal, Wiedemann, hep-th/0605178] using Euclidean string configurations since those authors advocate [hep-th/0607062, footnote 14] the use of spacelike Lorentzian string configurations instea

Phases of Braneworlds, Spinning D3-branes and Strongly-Coupled Gauge Theories

A spinning nonextremal D3-brane undergoes a phase transition to a naked singularity which, from the braneworld point of view, corresponds to the apparent graviton speed passing from subluminal to superluminal. We investigate this phase transition from the dual perspectives of braneworld scenarios and holography. We discuss the relevance of the thermodynamic stability domains of a spinning D3-brane to the physics of braneworld scenarios. We also describe various gravitational Lorentz violations which arise from static D3-branes.Comment: 18 pages, 6 figures, LaTeX, additional comment and reference