We prove that while the total cross section is bounded by $(\pi /m_{\pi }^2){ln}^{2}s$, where $s$ is the square of the c.m. energy and $m_{\pi }$ the mass of the pion, the total inelastic cross section is bounded by $(1/4)(\pi /m_{\pi }^2){ln}^{2}s$, which is 4 times smaller. We discuss the implications of this result on the total cross section itself.

Accuracy standards have been developed to ensure that the waveforms used for gravitational-wave data analysis are good enough to serve their intended purposes. These standards place constraints on certain norms of the frequency-domain representations of the waveform errors. Examples are given here of possible misinterpretations and misapplications of these standards, whose effect could be to vitiate the quality control they were intended to enforce. Suggestions are given for ways to avoid these problems.

In four space-time dimensions, there are good theoretical reasons for believing that general relativity is the correct geometrical theory of gravity, at least at the classical level. If one admits the possibility of extra space-time dimensions, what would we expect classical gravity to be like? It is often stated that the most natural generalization is Lovelock’s theory, which shares many physical properties with general relativity. But there are also key differences and problems. A potentially serious problem is the breakdown of determinism, which can occur when the matrix of coefficients of second time derivatives of the metric degenerates. This can be avoided by imposing inequalities on the curvature. Here it is argued that such inequalities occur naturally if the Lovelock action is obtained from Weyl’s formulas for the volume and surface area of a tube. Part of the purpose of this article is to give a treatment of the Weyl tube formula in terminology familiar to relativists and to give an appropriate (straightforward) generalization to a tube embedded in Minkowski space.

We discuss solar system constraints on $f(\mathcal{G})$ gravity models, where $f$ is a function of the Gauss-Bonnet term $\mathcal{G}$. We focus on cosmologically viable $f(\mathcal{G})$ models that can be responsible for late-time cosmic acceleration. These models generally give rise to corrections of the form $ϵ(r/r_s{)}^p$ to the vacuum Schwarzschild solution, where $\epsilon =H_{*}^2{r}_s^2\ll 1$, $r_s$ is the Schwarzschild radius of the Sun, and $H_{*}$ is the Hubble parameter today. We generally estimate the strength of modifications to general relativity in order to confront models with a number of experiments, such as the deflection of light and the perihelion shift. We show that cosmologically viable $f(\mathcal{G})$ models can be consistent with solar system constraints for a wide range of model parameters.

We propose a new approach, based on the puncture method, to construct black hole initial data in the so-called trumpet geometry, i.e. on slices that asymptote to a limiting surface of nonzero areal radius. Our approach is easy to implement numerically and, at least for nonspinning black holes, does not require any internal boundary conditions. We present numerical results, obtained with a uniform-grid finite-difference code, for boosted black holes and binary black holes. We also comment on generalizations of this method for spinning black holes.

In the minimal supersymmetric standard model with three generations of fermions, there is a stringent upper bound on the mass of the lightest neutral Higgs $h$, and the mass of the charged Higgs $H^{+}$ must be close (within tens of GeV) to the heavier neutral Higgs $H$ and the pseudoscalar Higgs $A$. In this paper, we show that in the four generation minimal supersymmetric standard model, the upper bound on the $h$ mass is much higher, as high as 400 GeV, and $H^{+}$ is generally much heavier than the $A$, allowing the $H^{+}\to A{W}^{+}$ decay, potentially changing search strategies for both the charged Higgs and the pseudoscalar. The $H$ mass, on the other hand, remains within tens of GeV of the charged Higgs mass.

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at $2\sigma$. In this letter, we explore the possibility of reconciling the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.

Calculation of the vacuum polarization, $⟨{\varphi }^2(x)⟩$, and expectation value of the stress tensor, $⟨T_{\mu \nu }(x)⟩$, has seen a recent resurgence, notably for black hole spacetimes. To date, most calculations of this type have been done only in four dimensions. Extending these calculations to $d$ dimensions includes $d$-dimensional renormalization. Typically, the renormalizing terms are found from Christensen’s covariant point splitting method for the DeWitt-Schwinger expansion. However, some manipulation is required to put the correct terms into a form that is compatible with problems of the vacuum polarization type. Here, after a review of the current state of affairs for $⟨{\varphi }^2(x)⟩$ and $⟨T_{\mu \nu }(x)⟩$ calculations and a thorough introduction to the method of calculating $⟨{\varphi }^2(x)⟩$, a compact expression for the DeWitt-Schwinger renormalization terms suitable for use in even-dimensional spacetimes is derived. This formula should be useful for calculations of $⟨{\varphi }^2(x)⟩$ and $⟨T_{\mu \nu }(x)⟩$ in even dimensions, and the renormalization terms are shown explicitly for four and six dimensions. Furthermore, use of the finite terms of the DeWitt-Schwinger expansion as an approximation to $⟨{\varphi }^2(x)⟩$ for certain spacetimes is discussed, with application to four and five dimensions.

We discuss the chiral phase transition in hot and dense QCD with three light flavors. Inspired by the well-known fact that the $U_{\mathrm{A}}(1)$ anomaly could induce first order phase transitions, we study the effect of the possible restoration of the $U_{\mathrm{A}}(1)$ symmetry at finite density. In particular, we explore the link between the $U_{\mathrm{A}}(1)$ restoration and the recent lattice QCD results of de Forcrand and Philipsen, in which the first order phase transition region near zero chemical potential ($\mu$) shrinks in the quark mass and $\mu$ space when $\mu$ is increased. Starting from the Ginzburg-Landau theory for general discussions, we then use the Nambu–Jona-Lasinio model for quantitative studies. With the partial $U_{\mathrm{A}}(1)$ restoration modeled by the density dependent ’t Hooft interaction, we fit the shrinking of the first order region found in de Forcrand and Philipsen’s lattice calculation at low $\mu$. At higher $\mu$, the first order region might shrink or expand, depending on the scenarios. This raises the possibility that despite the shrinking of the first order region at lower $\mu$, the QCD critical end point might still exist due to the expansion at higher $\mu$. In this case, very high precision lattice data will be needed to detect the recently observed backbending of the critical surface with the currently available analytic continuation or Taylor expansion approaches. Lattice computations could, however, test whether the $U_{\mathrm{A}}(1)$ restoration is responsible for the shrinking of the first order region by computing the ${\eta }^{\prime }$ mass or the topological susceptibility at small $\mu$.

We present a signature-based search for the anomalous production of events containing a photon, two jets, of which at least one is identified as originating from a $b$ quark, and missing transverse energy (${\mathrm{E̸}}_T$). The search uses data corresponding to $2.0{\mathrm{fb}}^{-1}$ of integrated luminosity from $p\overline{p}$ collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$, collected with the CDF II detector at the Fermilab Tevatron. From $6.69747\times {10}^6$ events with a photon candidate with transverse energy $E_T>25\mathrm{GeV}$, we find 617 events with ${\mathrm{E̸}}_T>25\mathrm{GeV}$ and two or more jets with $E_T>15\mathrm{GeV}$, at least one identified as originating from a $b$ quark, versus an expectation of $607\pm 113$ events. Increasing the requirement on ${\mathrm{E̸}}_T$ to 50 GeV, we find 28 events versus an expectation of $30\pm 11$ events. We find no indications of non-standard-model phenomena.

We have studied the $\varphi (1020)f_0(980)$ $S$-wave scattering at energies around threshold employing chiral Lagrangians coupled to vector mesons through minimal coupling. The interaction kernel is obtained by considering the $f_0(980)$ as a $K\overline{K}$ bound state. The $Y(2175)$ resonance is generated in this approach by the self-interactions between the $\varphi (1020)$ and the $f_0(980)$ resonances. We are able to describe the $e^{+}{e}^{-}\to \varphi (1020)f_0(980)$ recent scattering data to test experimentally our scattering amplitudes, concluding that the $Y(2175)$ resonance has a large $\varphi (1020)f_0(980)$ meson-meson component.

We study the reaction $e^{+}{e}^{-}\to e^{+}{e}^{-}{\pi }^0$ in the single tag mode and measure the differential cross section $d\sigma /d{Q}^2$ and the $\gamma {\gamma }^{*}\to {\pi }^0$ transition form factor in the momentum transfer range from 4 to $40{\mathrm{GeV}}^2$. At $Q^2>10{\mathrm{GeV}}^2$ the measured form factor exceeds the asymptotic limit predicted by perturbative QCD. The analysis is based on $442{\mathrm{fb}}^{-1}$ of integrated luminosity collected at PEP-II with the BABAR detector at $e^{+}{e}^{-}$ center-of-mass energies near 10.6 GeV.

We study four-dimensional interacting fermions in a strong magnetic field, using the holographic Sakai-Sugimoto model of intersecting D4- and D8-branes in the deconfined, chiral-symmetric parallel phase. We find that as the magnetic field is varied, while staying in the parallel phase, the fermions exhibit a first-order phase transition in which their magnetization jumps discontinuously. Properties of this transition are consistent with a picture in which some of the fermions jump to the lowest Landau level. Similarities to known magnetic phase transitions are discussed.

We show that there are universal high-temperature relations for transport coefficients of plasmas described by a wide class of field theories with gravity duals. These theories can be viewed as strongly coupled large-$N_c$ conformal field theories deformed by one or more relevant operators. The transport coefficients we study are the speed of sound and bulk viscosity, as well as the conductivity, diffusion coefficient, and charge susceptibility of probe $U(1)$ charges. We show that the sound bound $v_s^2\le 1/3$ is satisfied at high temperatures in these theories and also discuss bounds on the diffusion coefficient, the conductivity, and the bulk viscosity.

$\mathcal{N}=2$ superconformal many-body quantum mechanics in arbitrary dimensions is governed by a single scalar prepotential which determines the bosonic potential and the boson-fermion couplings. We present a special class of such models, for which the bosonic potential is absent. They are classified by homogeneous harmonic functions subject to physical symmetry requirements, such as translation, rotation and permutation invariance. The central charge is naturally quantized. We provide some examples for systems of identical particles in any dimension.

We uncover a novel solution of the ’t Hooft anomaly matching conditions for QCD. Interestingly in the perturbative regime the new gauge theory, if interpreted as a possible QCD dual, predicts the critical number of flavors above which QCD in the nonperturbative regime, develops an infrared stable fixed point. Remarkably this value is identical to the maximum bound predicted in the nonpertubative regime via the all-orders conjectured beta function for nonsupersymmetric gauge theories.

We show that a direct coupling between a chameleonlike scalar field and photons can give rise to a modified Sunyaev-Zel’dovich (SZ) effect in the cosmic microwave background (CMB). The coupling induces a mixing between chameleon particles and the CMB photons when they pass through the magnetic field of a galaxy cluster. Both the intensity and the polarization of the radiation are modified. The degree of modification depends strongly on the properties of the galaxy cluster such as magnetic field strength and electron number density. Existing SZ measurements of the Coma cluster enable us to place constraints on the photon-chameleon coupling. The constrained conversion probability in the cluster is ${\mathcal{P}}_{\mathrm{Coma}}(204\mathrm{GHz})<6.2\times {10}^{-5}$ at 95% confidence, corresponding to an upper bound on the coupling strength of $g_{\mathrm{eff}}^{(\mathrm{cell})}<2.2\times {10}^{-8}{\mathrm{GeV}}^{-1}$ or $g_{\mathrm{eff}}^{(\mathrm{Kolmo})}<(7.2–32.5)\times {10}^{-10}{\mathrm{GeV}}^{-1}$, depending on the model that is assumed for the cluster magnetic field structure. We predict the radial profile of the chameleonic CMB intensity decrement. We find that the chameleon effect extends farther toward the edges of the cluster than the thermal SZ effect. Thus we might see a discrepancy between the x-ray emission data and the observed SZ intensity decrement. We further predict the expected change to the CMB polarization arising from the existence of a chameleonlike scalar field. These predictions could be verified or constrained by future CMB experiments.

We extend to curved backgrounds all flat-space scalar field models that obey purely second-order equations, while maintaining their second-order dependence on both field and metric. This extension simultaneously restores to second order the, originally higher derivative, stress tensors as well. The process is transparent and uniform for all dimensions.

We investigate the properties of interacting $Q$-balls and boson stars that sit on top of each other in great detail. The model that describes these solutions is essentially a (gravitating) two-scalar field model where both scalar fields are complex. We construct interacting $Q$-balls or boson stars with arbitrarily small charges but finite mass. We observe that in the interacting case—where the interaction can be either due to the potential or due to gravity—two types of solutions exist for equal frequencies: one for which the two-scalar fields are equal, but also one for which the two-scalar fields differ. This constitutes a symmetry breaking in the model. While for $Q$-balls asymmetric solutions have always corresponding symmetric solutions and are thus likely unstable to decay to symmetric solutions with lower energy, there exists a parameter regime for interacting boson stars, where only asymmetric solutions exist. We present the domain of existence for two interacting nonrotating solutions as well as for solutions describing the interaction between rotating and nonrotating $Q$-balls and boson stars, respectively.