We compute, in the MSSM framework, the total electroweak contributions at one loop for the process $pp\to tW+X$, initiated by the parton process $bg\to tW$. The supersymmetric effect is analyzed for various choices of the SUSY benchmark points. Choosing realistic unpolarized and polarized experimental quantities, we show the size of the various effects and discuss their dependence on the MSSM parameters.

The effects of small Lorentz-violating terms on Bose-Einstein condensates are analyzed. We find that there are changes to the phase and shape of the ground-state wave function that vary with the orientation of the trap. In addition, spin couplings can act as a source for spontaneous symmetry breaking in ferromagnetic condensates making them sensitive probes for fundamental symmetry violation.

Using the Hamiltonian constraint derived by Ashtekar and Bojowald, we look for preclassical wave functions in the Schwarzschild interior. In particular, when solving this difference equation by separation of variables, an inequality is obtained relating the Immirzi parameter $\gamma$ to the quantum ambiguity $\delta$ appearing in the model. This bound is violated when we use a natural value for $\delta$ based on loop quantum gravity together with a recent proposal for $\gamma$. We also present numerical solutions of the constraint.

Based on the recent understanding of the role of the densitized lapse function in Einstein’s equations and of the proper way to pose the thin sandwich problem, a slight readjustment of the minimal distortion shift gauge in the $3+1$ approach to the dynamics of general relativity allows this shift vector to serve as the vector potential for the longitudinal part of the extrinsic curvature tensor in the new approach to the initial value problem, thus extending the initial value decomposition of gravitational variables to play a role in the evolution as well. The new shift vector globally minimizes the changes in the conformal 3-metric with respect to the spacetime measure rather than the spatial measure on the time coordinate hypersurfaces, as the old shift vector did.

We consider 5D Einstein-Maxwell (EM) gravity in spacetimes with three commuting Killing vectors: one timelike and two spacelike Killing vectors one of them being hypersurface orthogonal. Assuming a special ansatz for the Maxwell field we show that the 2-dimensional reduced EM equations are completely integrable by deriving a Lax-pair presentation. We also develop a solution generating method for explicit construction of exact EM solutions with considered symmetries. We also derive explicitly a new rotating six parametric 5D EM solution which includes the dipole black ring solution as a particular case.

The emission of electromagnetic waves from a system described by the Hénon-Heiles potential is studied in this work. The main aim is to analyze the behavior of the system when the damping term is included explicitly in the equations of motion. Energy losses at the chaotic regime and at the regular regime are compared. The results obtained here are similar to the case of gravitational waves emission, as long as we consider only the energy loss. The main difference is that in the present work the energy emitted is explicitly calculated solving the equation of motion without further approximations. It is expected that the present analysis may be useful when studying the analogous problem of dissipation in gravitational systems.

Numerical simulations of binary neutron stars by Wilson, Mathews, and Marronetti indicated that neutron stars that are stable in isolation can be made to collapse to black holes when placed in a binary. This claim was surprising as it ran counter to the Newtonian expectation that a neutron star in a binary should be more stable, not less. After correcting an error found by Flanagan, Wilson and Mathews found that the compression of the neutron stars was significantly reduced but not eliminated. This has motivated us to ask the following general question: Under what circumstances can general-relativistic tidal interactions cause an otherwise stable neutron star to be compressed? We have found that if a nonrotating neutron star possesses a current-quadrupole moment, interactions with a gravitomagnetic tidal field can lead to a compressive force on the star. If this current quadrupole is induced by the gravitomagnetic tidal field, it is related to the tidal field by an equation-of-state-dependent constant called the gravitomagnetic Love number. This is analogous to the Newtonian Love number that relates the strength of a Newtonian tidal field to the induced mass quadrupole moment of a star. The compressive force is almost never larger than the Newtonian tidal interaction that stabilizes the neutron star against collapse. In the case in which a current quadrupole is already present in the star (perhaps as an artifact of a numerical simulation), the compressive force can exceed the stabilizing one, leading to a net increase in the central density of the star. This increase is small ($\lesssim 1\%$) but could, in principle, cause gravitational collapse in a star that is close to its maximum mass. This paper also reviews the history of the Wilson-Mathews-Marronetti controversy and, in an appendix, extends the discussion of tidally induced changes in the central density to rotating stars.

Recently Ehlers, Ozsváth, and Schucking discussed whether pressure contributes to active gravitational mass as required by general relativity. They pointed out that there is no experimental information on this available, though precision measurement of the gravitational constant should provide a test of this foundational aspect of gravity. We had used a similar argument earlier to test the contribution of leptons to the active gravitational mass. In this paper we use the result from the Zürich gravitational constant experiment to provide the first adequate experimental input regarding the active gravitational mass of Fermi pressure. Apart from confirming the equality of the passive and active gravitational roles of the pressure term in general relativity within an accuracy of 5%, our results are consistent with the theoretical expectation of the cancellation of the gravity of pressure by the gravity of the surface tension of confined matter. This result on the active gravitational mass of the quantum zero-point Fermi pressure in the atomic nucleus is also interesting from the point of view of studying the interplay between quantum physics and classical gravity.

We present measurements of the flavor-changing neutral current decays $B\to K{\ell }^{+}{\ell }^{-}$ and $B\to K^{*}{\ell }^{+}{\ell }^{-}$, where ${\ell }^{+}{\ell }^{-}$ is either an $e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$ pair. The data sample comprises $229\times {10}^6{\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage ring. Flavor-changing neutral current decays are highly suppressed in the standard model and their predicted properties could be significantly modified by new physics at the electroweak scale. We measure the branching fractions $\mathcal{B}(B\to K{\ell }^{+}{\ell }^{-})=(0.34\pm 0.07\pm 0.02)\times {10}^{-6}$, $\mathcal{B}(B\to K^{*}{\ell }^{+}{\ell }^{-})=({0.78}_{-0.17}^{+0.19}\pm 0.11)\times {10}^{-6}$, the direct $CP$ asymmetries of these decays, and the relative abundances of decays to electrons and muons. For two regions in ${\ell }^{+}{\ell }^{-}$ mass, above and below $m_{J/\psi }$, we measure partial branching fractions and the forward-backward angular asymmetry of the lepton pair. In these same regions we also measure the $K^{*}$ longitudinal polarization in $B\to K^{*}{\ell }^{+}{\ell }^{-}$ decays. Upper limits are obtained for the lepton-flavor-violating decays $B\to Ke\mu$ and $B\to K^{*}e\mu$. All measurements are consistent with standard model expectations.

We consider a multilevel hydrogen atom in interaction with the quantum electromagnetic field and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy of the atom for uniform acceleration. It is found that the acceleration disturbs the vacuum fluctuations in such a way that the delicate balance between the contributions of vacuum fluctuation and radiation reaction that exists for inertial atoms is broken, so that the transitions to higher-lying states from ground state are possible even in vacuum. In contrast to the case of an atom interacting with a scalar field, the contributions of both electromagnetic vacuum fluctuations and radiation reaction to the spontaneous emission rate are affected by the acceleration, and furthermore the contribution of the vacuum fluctuations contains a nonthermal acceleration-dependent correction, which is possibly observable.

We exhibit the super-Higgs effect in heterotic string theory by turning on a background antisymmetric tensor $B$ field and deforming the Becchi-Rouet-Stora-Tyutin operator consistent with superconformal invariance. The $B$ field spontaneously breaks spacetime supersymmetry. We show how the gravitini and the physical dilatini gain mass by eating the would-be Goldstone fermions.

We review recent results on twisted noncommutative quantum field theory by embedding it into a general framework for the quantization of systems with a twisted symmetry. We discuss commutation relations in this setting and show that the twisted structure is so rigid that it is hard to derive any predictions, unless one gives up general principles of quantum theory. It is also shown that the twisted structure is not responsible for the presence or absence of UV/IR-mixing, as claimed in the literature.

We give a model of the higher-dimensional spherically symmetric gravitational collapse of a dust cloud including the perturbative effects of quantum gravity. The $n(\ge 5)$-dimensional action with the Gauss-Bonnet term for gravity is considered and a simple formulation of the basic equations is given for the spacetime $M\approx M^2\times K^{n-2}$ with a perfect fluid and a cosmological constant. This is a generalization of the Misner-Sharp formalism of the four-dimensional spherically symmetric spacetime with a perfect fluid in general relativity. The whole picture and the final fate of the gravitational collapse of a dust cloud differ greatly between the cases with $n=5$ and $n\ge 6$. There are two families of solutions, which we call plus-branch and the minus-branch solutions. A plus-branch solution can be attached to the outside vacuum region which is asymptotically anti-de Sitter in spite of the absence of a cosmological constant. Bounce inevitably occurs in the plus-branch solution for $n\ge 6$, and consequently singularities cannot be formed. Since there is no trapped surface in the plus-branch solution, the singularity formed in the case of $n=5$ must be naked. On the other hand, a minus-branch solution can be attached to the outside asymptotically flat vacuum region. We show that naked singularities are massless for $n\ge 6$, while massive naked singularities are possible for $n=5$. In the homogeneous collapse represented by the flat Friedmann-Robertson-Walker solution, the singularity formed is spacelike for $n\ge 6$, while it is ingoing-null for $n=5$. In the inhomogeneous collapse with smooth initial data, the strong cosmic censorship hypothesis holds for $n\ge 10$ and for $n=9$ depending on the parameters in the initial data, while a naked singularity is always formed for $5\le n\le 8$. These naked singularities can be globally naked when the initial surface radius of the dust cloud is fine-tuned, and then the weak cosmic censorship hypothesis is violated.

We study constraints on models with a flat universal extra dimension in which all standard model fields propagate in the bulk. A significantly improved constraint on the compactification scale is obtained from the extended set of electroweak precision observables accurately measured at LEP1 and LEP2. We find a lower bound of $M_c\equiv R^{-1}>700(800)\mathrm{GeV}$ at the 99% (95%) confidence level. We also discuss the implications of this constraint on the prospects for the direct and indirect detection of Kaluza-Klein dark matter in this model.

Unitarity cuts are widely used in analytic computation of loop amplitudes in gauge theories such as QCD. We expand upon the technique introduced in hep-ph/0503132 to carry out any finite unitarity cut integral. This technique naturally separates the contributions of bubble, triangle and box integrals in one-loop amplitudes and is not constrained to any particular helicity configurations. Loop momentum integration is reduced to a sequence of algebraic operations. We discuss the extraction of the residues at higher-order poles. Additionally, we offer concise algebraic formulas for expressing coefficients of three-mass triangle integrals. As an application, we compute all remaining coefficients of bubble and triangle integrals for nonsupersymmetric six-gluon amplitudes.

We consider the calculation of amplitudes for processes that take place in a constant background magnetic field, first using the standard method for the calculation of an amplitude in an external field, and second utilizing the Schwinger propagator for charged particles in a magnetic field. We show that there are processes for which the Schwinger-propagator method does not yield the total amplitude. We explain why the two methods yield equivalent results in some cases and indicate when we can expect the equivalence to hold. We show these results in fairly general terms and illustrate them with specific examples as well.

We generalize the quasilocal definition of the stress-energy tensor of Einstein gravity to the case of third order Lovelock gravity, by introducing the surface terms that make the action well-defined. We also introduce the boundary counterterm that removes the divergences of the action and the conserved quantities of the solutions of third order Lovelock gravity with zero curvature boundary at constant $t$ and $r$. Then, we compute the charged rotating solutions of this theory in $n+1$ dimensions with a complete set of allowed rotation parameters. These charged rotating solutions present black hole solutions with two inner and outer event horizons, extreme black holes or naked singularities provided the parameters of the solutions are suitably chosen. We compute temperature, entropy, charge, electric potential, mass and angular momenta of the black hole solutions, and find that these quantities satisfy the first law of thermodynamics. We find a Smarr-type formula and perform a stability analysis by computing the heat capacity and the determinant of Hessian matrix of mass with respect to its thermodynamic variables in both the canonical and the grand-canonical ensembles, and show that the system is thermally stable. This is commensurate with the fact that there is no Hawking-Page phase transition for black objects with zero curvature horizon.

A wide variety of vacua, and their cosmological realization, may provide an explanation for the apparently anthropic choices of some parameters of particle physics and cosmology. If the probability on various parameters is weighted by volume, a flat potential for slow-roll inflation is also naturally understood, since the flatter the potential the larger the volume of the subuniverse. However, such inflationary landscapes have a serious problem, predicting an environment that makes it exponentially hard for observers to exist and giving an exponentially small probability for a moderate universe like ours. A general solution to this problem is proposed, and is illustrated in the context of inflaton decay and leptogenesis, leading to an upper bound on the reheating temperature in our subuniverse. In a particular scenario of chaotic inflation and nonthermal leptogenesis, predictions can be made for the size of $CP$ violating phases, the rate of neutrinoless double beta decay and, in the case of theories with gauge-mediated weak-scale supersymmetry, for the fundamental scale of supersymmetry breaking.

Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have detected a spectrum of gamma-rays from the galactic center region which extends from $\sim 200\mathrm{GeV}$ or lower, to at least $\sim 10\mathrm{TeV}$. Although the source of this radiation is not yet known, the spectrum appears to behave as a simple power-law, which is not the expectation for gamma-rays generated through the annihilation of dark matter particles. If instead we conclude that the source of these gamma-rays is astrophysical in origin, this spectrum will constitute a background for future dark matter searches using gamma-rays from this region. In this paper we study how this background will affect the prospects for experiments such as GLAST to detect dark matter in the galactic center. We find that only a narrow range of dark matter annihilation rates are potentially observable by GLAST given this newly discovered background and considering current constraints from EGRET and HESS. We also find that a detection of line emission, while not completely ruled out, is only possible for a very narrow range of dark matter models and halo profiles.