The emission of electromagnetic radiation by charges moving uniformly in a Lorentz-violating vacuum is studied. The analysis is performed within the classical Maxwell-Chern-Simons limit of the Standard-Model Extension and confirms the possibility of a Čerenkov-type effect. In this context, various properties of Čerenkov radiation including the rate, polarization, and propagation features, are discussed, and the backreaction on the charge is investigated. An interpretation of this effect supplementing the conventional one is given. The emerging physical picture leads to a universal methodology for studying the Čerenkov effect in more general situations.

We employ the $G$-structure formalism to study supersymmetric solutions of minimal and SU(2) gauged supergravities in seven dimensions admitting Killing spinors with an associated timelike Killing vector. The most general such Killing spinor defines a SU(3) structure. We deduce necessary and sufficient conditions for the existence of a timelike Killing spinor on the bosonic fields of the theories, and find that such configurations generically preserve one out of 16 supersymmetries. Using our general supersymmetric ansatz we obtain numerous new solutions, including squashed or deformed anti-de Sitter solutions of the gauged theory, and a large class of Gödel-like solutions with closed timelike curves.

The frequencies and damping times of the non radial oscillations of non rotating neutron stars are computed for a set of recently proposed equations of state (EOS) which describe matter at supranuclear densities. These EOS are obtained within two different approaches, the nonrelativistic nuclear many-body theory and the relativistic mean field theory, that model hadronic interactions in different ways leading to different composition and dynamics. Being the non radial oscillations associated to the emission of gravitational waves, we fit the eigenfrequencies of the fundamental mode and of the first pressure and gravitational-wave mode (polar and axial) with appropriate functions of the mass and radius of the star, comparing the fits, when available, with those obtained by Andersson and Kokkotas in 1998. We show that the identification in the spectrum of a detected gravitational signal of a sharp pulse corresponding to the excitation of the fundamental mode or of the first p-mode, combined with the knowledge of the mass of the star—the only observable on which we may have reliable information—would allow to gain interesting information on the composition of the inner core. We further discuss the detectability of these signals by gravitational detectors.

We solve for single distorted black hole initial data using the puncture method, where the Hamiltonian constraint is written as an elliptic equation in ${\mathbb{R}}^3$ for the nonsingular part of the metric conformal factor. With this approach we can generate isometric and nonisometric black hole data. For the isometric case, our data are directly comparable to those obtained by Bernstein et al., who impose isometry boundary conditions at the black hole throat. Our numerical simulations are performed using a parallel multigrid elliptic equation solver with adaptive mesh refinement. Mesh refinement allows us to use high resolution around the black hole while keeping the grid boundaries far away in the asymptotic region.

We study the generalized Chaplygin gas (GCG) scenario in a modified gravity approach. That is, we impose that our universe has a pure dust configuration, and allow for a modification of gravity that yields a GCG specific scale factor evolution. Moreover, assuming that this new hypothetical gravity theory obeys a generalization of Birkhoff's law, we determine the Schwarzschild-like metric in this new modified gravity. We also study the large scale structure formation in this model. Both the linear and nonlinear growth are studied together with the growth of the velocity fluctuation in the linear perturbation theory. We compare our results with those corresponding to the $\Lambda$ Cold Dark Matter model and discuss possible distinguishable features.

We show that the chameleon scalar field can drive the current phase of cosmic acceleration for a large class of scalar potentials that are also consistent with local tests of gravity. These provide explicit realizations of a quintessence model where the quintessence scalar field couples directly to baryons and dark matter with gravitational strength. We analyze the cosmological evolution of the chameleon field and show the existence of an attractor solution with the chameleon following the minimum of its effective potential. For a wide range of initial conditions, spanning many orders of magnitude in initial chameleon energy density, the attractor is reached before nucleosynthesis. Surprisingly, the range of allowed initial conditions leading to a successful cosmology is wider than in normal quintessence. We discuss applications to the cyclic model of the universe and show how the chameleon mechanism weakens some of the constraints on cyclic potentials.

We present the complete set of propagation and constraint equations for the kinematic and nonlocal first order quantities which describe general linear inhomogeneous and anisotropic perturbations of a flat Friedmann-Robertson-Walker braneworld with vanishing cosmological constant and decompose them in the standard way into their scalar, vector and tensor contributions. A detailed analysis of the perturbation dynamics is performed using dimensionless variables that are specially tailored for the different regimes of interest; namely, the low energy general relativity regime, the high energy regime and the dark energy regime. Tables are presented for the evolution of all the physical quantities, making it easy to do a detailed comparison of the past asymptotic behavior of the perturbations of these models. We find results that exactly match those obtained in the analysis of the spatially inhomogeneous $G_2$ braneworld cosmologies presented recently; i.e., that isotropization towards the ${\mathcal{F}}_b$ model occurs for $\gamma >4/3$.

Recent data advances offer the exciting prospect of a first look at whether dark energy has a dynamical equation of state or not. While formally theories exist with a constant equation of state, they are nongeneric—Einstein’s cosmological constant is a notable exception. So limits on the time variation, $w^{\prime }$, directly tell us crucial physics. Two recent improvements in supernova data from the Hubble space telescope allow important steps forward in constraining the dynamics of dark energy, possessing the ability to exclude models with $w^{\prime }\gtrsim 1$, if the universe truly has a cosmological constant. These data bring us much closer to the “systematics” era, where further improvements will come predominantly from more accurate, not merely more, observations. We examine the possible gains and point out the complementary roles of space and ground based observations in the near future. To achieve the leap to precision understanding of dark energy in the next generation will require specially designed space based measurements; we estimate the confidence level of detection of dynamics (e.g., distinguishing between $w^{\prime }=0$ and $w^{\prime }=1$) will be $\sim 1.8\sigma$ after the ongoing generation, improving to more than $6.5\sigma$ in the dedicated space generation.

The motion of sound waves propagating in the perfect fluid with inhomogeneous background flow is effectively described as a massless scalar field on a curved space-time. This effective geometry is characterized by the acoustic metric, which depends on the background flow, and null geodesics on the geometry express the acoustic causal structure. Therefore by the effective geometry we can easily study the causality on the flows. In this paper, we consider a spherically symmetric, relativistic outflow and present the maximal causally connected region for a supersonic flow, which is a simple analog of gamma-ray bursts (GRBs). Causality in GRB outflows is important when we consider the coherency of the magnetic field. When the Lorentz factor of the radial velocity of the flow is constant or obeys the power law with respect to the radial coordinate $r$, we can solve it analytically. As a result we show that in the constant case the maximum angle is proportional to the inverse of the Lorentz factor and logarithmically increases with respect to $r$; in contrast, accelerative expansions in the power-law case make this angle bounded.

We present a unified picture of flavor and electroweak symmetry breaking based on a nonlinear sigma model spontaneously broken at the TeV scale. Flavor and Higgs bosons arise as pseudo-Goldstone modes. Explicit collective symmetry breaking yields stable vacuum expectation values and masses protected at one loop by the little-Higgs mechanism. The coupling to the fermions generates well-defined mass textures—according to a U(1) global flavor symmetry—that correctly reproduce the mass hierarchies and mixings of quarks and leptons. The model is more constrained than usual little-Higgs models because of bounds on weak and flavor physics. The main experimental signatures testable at the LHC are a rather large mass $m_{h^0}=317\pm 80\mathrm{G}\mathrm{e}\mathrm{V}$ for the (lightest) Higgs boson and a characteristic spectrum of new bosons and fermions at the TeV scale.

In a preceding study in the heavy quark limit of QCD, it has been demonstrated that the best lower bound on the curvature of the Isgur-Wise function $\xi (w)$ is ${\xi }^{\prime \prime }(1)>\frac{1}{5}[4{\rho }^2+3({\rho }^2{)}^2]>\frac{15}{16}$. The quadratic term $({\rho }^2{)}^2$ is dominant in a nonrelativistic expansion in the light quark, both ${\xi }^{\prime \prime }(1)$ and $({\rho }^2{)}^2$ scaling like $(R^2{m}_q^2{)}^2$, where $m_q$ is the light quark mass and $R$ the bound state radius. The nonrelativistic limit is thus a good guideline in the study of the shape of $\xi (w)$. In the present paper we obtain similar bounds on all the derivatives of ${\xi }_{\mathrm{N}\mathrm{R}}(w)$, the IW function with the light quark nonrelativistic, and we demonstrate that these bounds are optimal. Our general method is based on the positivity of matrices of moments of the ground state wave function, that allows to bound the $n$th derivative ${\xi }_{\mathrm{N}\mathrm{R}}^{(n)}(w)$ in terms of the $m$th ones ($m<n$). We show that the method can be generalized to the true Isgur-Wise function of QCD $\xi (w)$.

Final state phases ${\delta }_f$ and ${\delta }_f^{\prime }$ in $B\to D\pi$, $\overline{D}\pi$ decays are shown to be equal, i.e., $\delta ={\delta }_f-{\delta }_f^{\prime }=0$. Thus $CP$-violating asymmetry $\mathcal{A}(t)$ is independent of final state phases. The estimate for the phases ${\delta }_f$ and ${\delta }_f^{\prime }$ is also given.

We show how LHC Higgs boson production and decay data can be used to extract gauge and fermion couplings of Higgs bosons. We show that very mild theoretical assumptions, which are valid in general multi-Higgs doublet models, are sufficient to allow the extraction of absolute values for the couplings rather than just ratios of the couplings. For Higgs masses below 200 GeV we find accuracies of $10-40\%$ for the Higgs boson couplings and total width after several years of LHC running. Slightly stronger assumptions on the Higgs gauge couplings even lead to a determination of couplings to fermions at the level of $10-20\%$. We also study the sensitivity to deviations from SM predictions in several supersymmetric benchmark scenarios as a subset of the analysis.

The effects of compact extra dimensions upon quantum stress tensor fluctuations are discussed. It is argued that as the compactification volume decreases, these fluctuations increase in magnitude. In principle, this would have the potential to create observable effects, such as luminosity fluctuations or angular blurring of distant sources, and lead to constraints upon Kaluza-Klein theories. However, the dependence of the four-dimensional Newton’s constant upon the compactification volume causes the gravitational effects of the stress tensor fluctuations to be finite in the limit of small volume. Consequently, no observational constraints upon Kaluza-Klein theories are obtained.

We study the effective action of the heterotic string compactified on particular half-flat manifolds which arise in the context of mirror symmetry with Neveu-Schwarz–Neveu-Schwarz flux. We explicitly derive the superpotential and Kähler potential at lowest order in ${\alpha }^{\prime }$ by a reduction of the bosonic action. The superpotential contains new terms depending on the Kähler moduli which originate from the intrinsic geometrical flux of the half-flat manifolds. A generalized Gukov formula, valid for all manifolds with SU(3) structure, is derived from the gravitino mass term. For the half-flat manifolds it leads to a superpotential in agreement with our explicit bosonic calculation. We also discuss the inclusion of gauge fields.

We discuss various realizations of the four-dimensional braneworld inflation in warped geometries of string theory. In all models the inflaton field is represented by a $Dp$ probe brane scalar specifying its position in the warped throat of the compactification manifold. We study existing inflationary throat local geometries, and construct a new example. The inflationary brane is either a $D3$ or a $D5$ brane of type IIB string theory. In the latter case the inflationary brane is wrapping a two-cycle of the compactification manifold. We discuss some phenomenological aspects of the model where slow-roll conditions are under computational control.

It seems likely that string theory has a landscape of vacua that includes very many metastable de Sitter spaces. However, as emphasized by Banks, Dine, and Gorbatov, no current framework exists for examining these metastable vacua in string theory. In this paper we attempt to correct this situation by introducing an eternally inflating background in which the entire collection of accelerating cosmologies is present as intermediate states. The background is a classical solution which consists of a bubble of zero cosmological constant inside de Sitter space, separated by a domain wall. At early and late times the flat space region becomes infinitely big, so an S-matrix can be defined. Quantum mechanically, the system can tunnel to an intermediate state which is pure de Sitter space. We present evidence that a string theory S-matrix makes sense in this background, and that it contains metastable de Sitter space as an intermediate state.

In a recent companion paper, we observed that the rules of ordinary thermodynamics generally fail to respect thermal duality, a symmetry of string theory under which the physics at temperature $T$ is related to the physics at the inverse temperature $1/T$. Even when the free energy and internal energy exhibit the thermal duality symmetry, the entropy and specific heat are defined in such a way that this symmetry is destroyed. In this paper, we propose a modification of the traditional definitions of these quantities, yielding a manifestly duality-covariant thermodynamics. At low temperatures, these modifications produce corrections to the standard definitions of entropy and specific heat which are suppressed by powers of the string scale. These corrections may nevertheless be important for the full development of a consistent string thermodynamics. We find, for example, that the string-corrected entropy can be smaller than the usual entropy at high temperatures, suggesting a possible connection with the holographic principle. We also discuss some outstanding theoretical issues prompted by our approach.

Thermal duality, which relates the physics of closed strings at temperature $T$ to the physics at the inverse temperature $1/T$, is one of the most intriguing features of string thermodynamics. Unfortunately, the classical definitions of thermodynamic quantities such as entropy and specific heat are not invariant under the thermal duality symmetry. In this paper, we investigate whether there might nevertheless exist special solutions for the string effective potential such that the duality symmetry will be preserved for all thermodynamic quantities. Imposing this as a constraint, we derive a series of unique functional forms for the complete temperature dependence of the required string effective potentials. Moreover, we demonstrate that these solutions successfully capture the leading temperature behavior of a variety of actual one-loop effective potentials for duality-covariant finite-temperature string ground states. This leads us to conjecture that our solutions might actually represent the exact effective potentials when contributions from all orders of perturbation theory are included.