The effective equation of state of normal matter is changed in theories where the size of the compact space depends upon the local energy density. In particular we show how the dilution of a fluid due to the expansion of the universe can be compensated by an increase of the effective coupling of that fluid to gravity in the presence of a potential which acts to reduce the size of the compact space. We estimate how much cosmic acceleration can be obtained in such a model and comment on the difficulties faced in finding an appropriate potential.

An interacting scalar field theory in de Sitter space appears to be nonrenormalizable for a generic $\alpha$-vacuum state. This pathology arises since the usual propagator used allows for a constructive interference among propagators in loop corrections, which produces divergences that are not proportional to standard counterterms. This interference can be avoided by defining a new propagator for the $\alpha$-vacuum based on a generalized time-ordering prescription. The generating functional associated with this propagator contains a source that couples to the field both at a point and at its antipode. To one loop order, we show that a set of theories with very general antipodal interactions is causal and renormalizable.

We show that previously known non-asymptotically flat static black hole solutions of Einstein-Maxwell-dilaton theory may be obtained as near-horizon limits of asymptotically flat black holes. Specializing to the case of the dilaton coupling constant ${\alpha }^2=3$, we generate from the non-asymptotically flat magnetostatic or electrostatic black holes two classes of rotating dyonic black hole solutions. The rotating dyonic black holes of the magnetic class are dimensional reductions of the five-dimensional Myers-Perry black holes relative to one of the azimuthal angles, while those of the electric class are twisted dimensional reductions of rotating dyonic Rasheed black strings. We compute the quasilocal mass and angular momentum of our rotating dyonic black holes and show that they satisfy the first law of black hole thermodynamics, as well as a generalized Smarr formula. We also discuss the construction of non-asymptotically flat multi-extreme black hole configurations.

Techniques are developed for projecting the solutions of symmetric-hyperbolic evolution systems onto the constraint submanifold (the constraint-satisfying subset of the dynamical field space). These optimal projections map a field configuration to the nearest configuration in the constraint submanifold, where distances between configurations are measured with the natural metric on the space of dynamical fields. The construction and use of these projections are illustrated for a new representation of the scalar field equation that exhibits both bulk and boundary generated constraint violations. Numerical simulations on a black hole background show that bulk constraint violations cannot be controlled by constraint-preserving boundary conditions alone, but are effectively controlled by constraint projection. Simulations also show that constraint violations entering through boundaries cannot be controlled by constraint projection alone, but are controlled by constraint-preserving boundary conditions. Numerical solutions to the pathological scalar field system are shown to converge to solutions of a standard representation of the scalar field equation when constraint projection and constraint-preserving boundary conditions are used together.

We study the generalized Unruh effect for accelerated reference frames that include rotation in addition to acceleration. We focus particularly on the case where the motion is planar, with the presence of a static limit in addition to the event horizon. Possible definitions of an accelerated vacuum state are examined and the interpretation of the Minkowski vacuum state as a thermodynamic state is discussed. Such a thermodynamic state is shown to depend on two parameters, the acceleration temperature and a drift velocity, which are determined by the acceleration and angular velocity of the accelerated frame. We relate the properties of the Minkowski vacuum in the accelerated frame to the excitation spectrum of a detector that is stationary in this frame. The detector can be excited both by absorbing positive energy quanta in the “hot” vacuum state and by emitting negative energy quanta into the “ergosphere” between the horizon and the static limit. The effects are related to similar effects in the gravitational field of a rotating black hole.

The stability of general relativistic thin disks is investigated under a general first order perturbation of the energy momentum tensor. In particular, we consider temporal, radial, and azimuthal “test matter” perturbations of the quantities involved on the plane $z=0$. We study the thin disks generated by applying the “displace, cut, and reflect” method, usually known as the image method, to the Schwarzschild metric in isotropic coordinates and to the Chazy-Curzon metric and the Zipoy-Voorhees metric ($\gamma$-metric) in Weyl coordinates. In the case of the isotropic Schwarzschild thin disk, where a radial pressure is present to support the gravitational attraction, the disk is stable and the perturbation favors the formation of rings. Also, we found the expected result that the thin disk models generated by the Chazy-Curzon and Zipoy-Voorhees metric with only azimuthal pressure are not stable under a general first order perturbation.

We reexamine here a problem considered in detail before by Waugh and Lake: the solution of spherically symmetric Einstein’s equations with a radial flow of unpolarized radiation (the Vaidya metric) in double-null coordinates. This problem is known to be not analytically solvable; the only known explicit solutions correspond to the constant mass case (Schwarzschild solution in Kruskal-Szekeres form) and the linear and exponential mass functions originally discovered by Waugh and Lake. We present here a semianalytical approach that can be used to discuss some qualitative and quantitative aspects of the Vaidya metric in double-null coordinates for generic mass functions. We present also a new analytical solution corresponding to $(1/v)$-mass function and discuss some physical examples.

We analyze the orbital motion of a light anti-D6-brane in the presence of a stack of heavy, distant D6-branes in ten dimensions, taking account of possible time variations in the background moduli fields. The Coulomb-like central potential arising through brane-antibrane interactions is then modified to include time-dependent prefactors, which generally preclude the existence of stable elliptical orbits.

Loop quantum gravity introduces strong nonperturbative modifications to the dynamical equations in the semiclassical regime, which are responsible for various novel effects, including resolution of the classical singularity in a Friedman universe. Here we investigate the modifications for the case of a cyclic universe potential, assuming that we can apply the four-dimensional loop quantum formalism within the effective four-dimensional theory of the cyclic scenario. We find that loop quantum effects can dramatically alter the near-collision dynamics of the cyclic scenario. In the kinetic-dominated collapse era, the scalar field is effectively frozen by loop quantum friction, so that the branes approach collision and bounce back without actual collision.

The neutralino, the lightest stable supersymmetric particle, is a strong theoretical candidate for the missing astronomical “dark matter”. A profusion of such neutralinos can accumulate near the Sun when they lose energy upon scattering and are gravitationally captured. Pair-annihilations of those neutralinos may produce very high-energy (VHE, above 100 GeV) gamma rays. Milagro is an air shower array which uses the water Cherenkov technique to detect extensive-air showers and is capable of observing VHE gamma rays from the direction of the Sun with an angular resolution of $0.75°$. Analysis of Milagro data with an exposure to the Sun of 1165 hours presents the first attempt to detect TeV gamma rays produced by annihilating neutralinos captured by the Solar system and shows no statistically significant signal. Resulting limits that can be set on the gamma-ray flux due to near-Solar neutralino annihilations and on the neutralino cross-section are presented.

We discuss the curvaton scenario with the Affleck-Dine baryogenesis. In this scenario, nonvanishing baryonic entropy fluctuation may be generated even without primordial fluctuation of the Affleck-Dine field. Too large entropy fluctuation is inconsistent with the observations and hence constraints on the curvaton scenario with the Affleck-Dine baryogenesis are obtained. We calculate the baryonic entropy fluctuation (as well as other cosmological density fluctuations) in this case and derive constraints. Implications to some of the models of the curvaton are also discussed.

It has been suggested that codimension-two braneworlds might naturally explain the vanishing of the 4D effective cosmological constant, due to the automatic relation between the deficit angle and the brane tension. To investigate whether this cancellation happens dynamically, and within the context of a realistic cosmology, we study a codimension-two braneworld with spherical extra dimensions compactified by magnetic flux. Assuming Einstein gravity, we show that when the brane contains matter with an arbitrary equation of state, the 4D metric components are not regular at the brane, unless the brane has nonzero thickness. We construct explicit 6D solutions with thick branes, treating the brane matter as a perturbation, and find that the universe expands consistently with standard Friedmann-Robertson-Walker (FRW) cosmology. The relation between the brane tension and the bulk deficit angle becomes $\Delta =2\pi G_6(\rho -3p)$ for a general equation of state. However, this relation does not imply a self-tuning of the effective 4D cosmological constant to zero; perturbations of the brane tension in a static solution lead to deSitter or anti-deSitter braneworlds. Our results thus confirm other recent work showing that codimension-two braneworlds in nonsupersymmetric Einstein gravity do not lead to a dynamical relaxation of the cosmological constant, but they leave open the possibility that supersymmetric versions can be compatible with self-tuning.

Quintessential inflation describes a scenario in which both inflation and dark energy (quintessence) are described by the same scalar field. In conventional braneworld models of quintessential inflation gravitational particle-production is used to reheat the universe. This reheating mechanism is very inefficient and results in an excessive production of gravity waves which violate nucleosynthesis constraints and invalidate the model. We describe a new method of realizing quintessential inflation on the brane in which inflation is followed by 'instant preheating' (Felder, Kofman & Linde 1999). The larger reheating temperature in this model results in a smaller amplitude of relic gravity waves which is consistent with nucleosynthesis bounds. The relic gravity wave background has a 'blue' spectrum at high frequencies and is a generic byproduct of successful quintessential inflation on the brane.

The modified Newtonian dynamics (MOND) paradigm of Milgrom can boast of a number of successful predictions regarding galactic dynamics; these are made without the assumption that dark matter plays a significant role. MOND requires gravitation to depart from Newtonian theory in the extragalactic regime where dynamical accelerations are small. So far relativistic gravitation theories proposed to underpin MOND have either clashed with the post-Newtonian tests of general relativity, or failed to provide significant gravitational lensing, or violated hallowed principles by exhibiting superluminal scalar waves or an a priori vector field. We develop a relativistic MOND inspired theory which resolves these problems. In it gravitation is mediated by metric, a scalar, and a 4-vector field, all three dynamical. For a simple choice of its free function, the theory has a Newtonian limit for nonrelativistic dynamics with significant acceleration, but a MOND limit when accelerations are small. We calculate the $\beta$ and $\gamma$ parameterized post-Newtonian coefficients showing them to agree with solar system measurements. The gravitational light deflection by nonrelativistic systems is governed by the same potential responsible for dynamics of particles. To the extent that MOND successfully describes dynamics of a system, the new theory’s predictions for lensing by that system’s visible matter will agree as well with observations as general relativity’s predictions made with a dynamically successful dark halo model. Cosmological models based on the theory are quite similar to those based on general relativity; they predict slow evolution of the scalar field. For a range of initial conditions, this last result makes it easy to rule out superluminal propagation of metric, scalar, and vector waves.

The ${\mathbf{27}}_{J=3/2}$-plet mass spectrum and the ${\mathbf{27}}_{3/2}-\overline{\mathbf{10}}$ mass splittings are computed in the framework of the minimal $\mathrm{S}\mathrm{U}(3{)}_f$ extended Skyrme model. As functions of the Skyrme charge $e$ and the $\mathrm{S}\mathrm{U}(3{)}_f$ symmetry breaking parameters the predictions are presented in tabular form. The predicted mass splitting ${\mathbf{27}}_{3/2}-\overline{\mathbf{10}}$ is the smallest among all $\mathrm{S}\mathrm{U}(3{)}_f$ baryonic multiplets, confirming earlier findings.

The seesaw mechanism that explains the small neutrino masses comes naturally with supersymmetric (SUSY) grand-unification and leptogenesis. However, the framework suffers from the SUSY flavor and CP problems, and has a severe cosmological gravitino problem. We propose anomaly mediation as a simple solution to all these problems, which is viable once supplemented by the $D$-terms for $U(1{)}_Y$ and $U(1{)}_{B-L}$. Even though the right-handed neutrino mass explicitly breaks $U(1{)}_{B-L}$ and hence reintroduces the flavor problem, we show that it lacks the logarithmic enhancement and poses no threat to the framework. The thermal leptogenesis is then made easily consistent with the gravitino constraint.

A thorough study of 4-dimensional SU(2) Yang-Mills theory in Coulomb gauge is performed using large scale lattice simulations. The (equal-time) transverse gluon propagator, the ghost form factor $d(p)$ and the Coulomb potential $V_{\mathrm{c}\mathrm{o}\mathrm{u}\mathrm{l}}(p)\propto d^2(p)f(p)/p^2$ are calculated. For large momenta $p$, the gluon propagator decreases like $1/p^{1+\eta }$ with $\eta =0.5(1)$. At low momentum, the propagator is weakly momentum dependent. The small momentum behavior of the Coulomb potential is consistent with linear confinement. We find that the inequality ${\sigma }_{\mathrm{c}\mathrm{o}\mathrm{u}\mathrm{l}}\ge \sigma$ is satisfied. Finally, we provide evidence that the ghost form factors $d(p)$ and $f(p)$ acquire IR singularities, i.e., $d(p)\propto 1/\sqrt{p}$ and $f(p)\propto 1/p$, respectively. It turns out that the combination $g_0^2{d}_0(p)$ of the bare gauge coupling $g_0$ and the bare ghost form factor $d_0(p)$ is finite and therefore renormalization group invariant.

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous trilinear vector-boson interactions $W^{+}{W}^{-}\gamma$ and $W^{+}{W}^{-}Z$ through the single production of electroweak gauge bosons via the weak boson fusion processes $qq\to qqW(\to {\ell }^{\pm }\nu )$ and $qq\to qqZ(\to {\ell }^{+}{\ell }^{-})$ with $\ell =e$ or $\mu$. After a careful study of the standard model backgrounds, we show that the single production of electroweak bosons at the LHC can provide stringent tests on deviations of these vertices from the standard model prediction. In particular, we show that single gauge-boson production exhibits a sensitivity to the couplings $\Delta {\kappa }_{Z,\gamma }$ similar to that attainable from the analysis of electroweak boson pair production.

Higgs-boson production in association with bottom quarks, $p\overline{p}/pp\to b\overline{b}H+X,$ is one of the most important discovery channels for supersymmetric Higgs particles at the Tevatron and the LHC. We have calculated the next-to-leading-order QCD corrections to the parton processes $q\overline{q},gg\to b\overline{b}H$ and present results for total cross sections and for distributions in the transverse momenta of the bottom quarks. The QCD corrections reduce the renormalization and factorization scale dependence and thus stabilize the theoretical predictions, especially when the Higgs-boson is produced in association with high-$p_T$ bottom quarks. The next-to-leading-order predictions for the total cross-section are in reasonable numerical agreement with calculations based on bottom-quark fusion $b\overline{b}\to H$.

The relevance of intrinsic (or primordial) transverse momentum of partons in the inclusive production of particles at high energy and moderately large $p_T$ has been known for a long time, beginning with Drell-Yan and diphoton processes, and continuing with photon and meson production in hadronic collisions. In view of its renewed interest in the context of polarized processes and single spin asymmetries we perform, in the framework of perturbative QCD with the inclusion of spin and ${\mathit{k}}_{\perp }$ effects, a detailed analysis of several such processes in different kinematical situations. We show that the inclusion of these effects leads, at the level of accuracy reachable in this approach, to an overall satisfactory agreement between theoretical predictions and experimental unpolarized data, thus giving support to the study of spin effects and single spin asymmetries within the same scheme. We present results for transverse single spin asymmetries, generated by the so-called Sivers effect, in inclusive pion and photon production in proton-proton collisions. We compare our results with the available experimental data and with previous results obtained using simplified versions of this approach.