We compute QCD corrections to the production of a $t\overline{t}$ pair in association with a hard photon at the Tevatron and the LHC. This process allows a direct measurement of the top quark electromagnetic couplings that, at the moment, are only loosely constrained. We include top quark decays, treating them in the narrow width approximation, and retain spin correlations of final-state particles. Photon radiation off top quark decay products is included in our calculation and yields a significant contribution to the cross section. We study next-to-leading-order QCD corrections to the $p\overline{p}\to t\overline{t}\gamma$ process at the Tevatron for the selection criteria used in a recent measurement by the CDF collaboration. We also discuss the impact of QCD corrections to the $pp\to t\overline{t}\gamma$ process on the measurement of the top quark electric charge at the 14 TeV LHC.

We first present a nonresonant description to charmoniumlike structure $Y(4360)$ in the $\psi (2S){\pi }^{+}{\pi }^{-}$ invariant mass spectrum of the $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ process. The $Y(4360)$ structure is depicted well by the interference effect of the production amplitudes of $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ via the intermediate charmonia $\psi (4160)/\psi (4415)$ and direct $e^{+}{e}^{-}$ annihilation into $\psi (2S){\pi }^{+}{\pi }^{-}$. This fact shows that $Y(4360)$ is not a genuine resonance, which naturally explains why $Y(4360)$ was only reported in its hidden-charm decay channel $\psi (2S){\pi }^{+}{\pi }^{-}$ and was not observed in the exclusive open-charm decay channel or $R$-value scan.

In the two-Higgs-doublet model the alignment of the Yukawa matrices in flavor space guarantees the absence of flavor-changing neutral currents at tree level, while introducing new sources for $CP$ violation parametrized in a very economical way [Antonio Pich and Paula Tuzon, Phys. Rev. D 80, 091702 (2009)]. This implies a potentially large influence in a number of processes, $b\to s\gamma$ being a prominent example where rather high experimental and theoretical precision meet. We analyze the $CP$ rate asymmetry in this inclusive decay and determine the resulting constraints on the model parameters. We demonstrate the compatibility with previously obtained limits [Martin Jung, Antonio Pich, and Paula Tuzon, J. High Energy Phys. 11 (2010) 003]. Moreover, we extend the phenomenological analysis of the branching ratio, and examine the influence of resulting correlations on the like-sign dimuon charge asymmetry in $B$ decays.

A measurement of the top-quark pair-production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using data corresponding to an integrated luminosity of $1.12{\mathrm{fb}}^{-1}$ collected with the Collider Detector at Fermilab is presented. Decays of top-quark pairs into the final states $e\nu +$ jets and $\mu \nu +$ jets are selected, and the cross section and the $b$-jet identification efficiency are determined using a new measurement technique which requires agreement between the measured cross sections with exactly one and with multiple identified $b$ quarks from the top-quark decays. Assuming a top-quark mass of $175\mathrm{GeV}/c^2$, a cross section of $8.5\pm 0.6(\mathrm{stat})\pm 0.7(\mathrm{syst})\mathrm{pb}$ is measured.

A Mellin-type representation of the graviton bulk-to-bulk propagator from E. D’Hoker, D. Z. Freedman, S. D. Mathur, A. Matusis, and L. Rastelli [Nucl. Phys. B562, 330 (1999)] in terms of the integral over the product of bulk-to-boundary propagators is derived.

A gauge-invariant, linear cosmological perturbation theory of an almost homogeneous and isotropic universe with dynamically evolving Newton constant $G$ and cosmological constant $\Lambda$ is presented. The equations governing the evolution of the comoving fractional spatial gradients of the matter density, $G$ and $\Lambda$, are thus obtained. Explicit solutions are discussed in cosmologies, featuring an accelerated expansion, where both $G$ and $\Lambda$ vary according to renormalization group equations in the vicinity of an ultraviolet fixed point. Finally, a similar analysis is carried out in the late universe regime described by the part of the renormalization group trajectory close to the Gaussian fixed point.

The Dirac-Born-Infeld (DBI) Galileons are a generalization of the Galileon terms, which extend the internal Galilean symmetry to an internal relativistic symmetry, and can also be thought of as generalizations of DBI which yield second order field equations. We show that, when considered as local modifications to gravity, such as in the Solar System, there exists a region of parameter space in which spherically symmetric static solutions exist and are stable. However, these solutions always exhibit superluminality, casting doubt on the existence of a standard Lorentz invariant UV completion.

We consider the effect of discretization errors on the microscopic spectrum of the Wilson Dirac operator using both chiral perturbation theory and chiral random matrix theory. A graded chiral Lagrangian is used to evaluate the microscopic spectral density of the Hermitian Wilson Dirac operator as well as the distribution of the chirality over the real eigenvalues of the Wilson Dirac operator. It is shown that a chiral random matrix theory for the Wilson Dirac operator reproduces the leading zero-momentum terms of Wilson chiral perturbation theory. All results are obtained for a fixed index of the Wilson Dirac operator. The low-energy constants of Wilson chiral perturbation theory are shown to be constrained by the Hermiticity properties of the Wilson Dirac operator.

We apply the nonlinear realizations method for constructing new Galilean conformal mechanics models. Our starting point is the Galilean conformal algebra which is a nonrelativistic contraction of its relativistic counterpart. We calculate Maurer-Cartan one-forms, examine various choices of the relevant coset spaces, and consider the geometric inverse Higgs-type constraints which reduce the number of the independent coset parameters and, in some cases, provide dynamical equations. New Galilean conformally invariant actions are derived in arbitrary space-time dimension $D=d+1$ (no central charges), as well as in the special dimension $D=2+1$ with one exotic central charge. We obtain new classical mechanics models which extend the standard ($D=0+1$) conformal mechanics in the presence of $d$ nonvanishing space dimensions.

We develop a new, mathematically precise framework for treating the effects of nonlinear phenomena occurring on small scales in general relativity. Our approach is an adaptation of Burnett’s formulation of the shortwave approximation, which we generalize to analyze the effects of matter inhomogeneities as well as gravitational radiation. Our framework requires the metric to be close to a background metric, but allows arbitrarily large stress-energy fluctuations on small scales. We prove that, within our framework, if the matter stress-energy tensor satisfies the weak energy condition (i.e., positivity of energy density in all frames), then the only effect that small-scale inhomogeneities can have on the dynamics of the background metric is to provide an effective stress-energy tensor that is traceless and has positive energy density—corresponding to the presence of gravitational radiation. In particular, nonlinear effects produced by small-scale inhomogeneities cannot mimic the effects of dark energy. We also develop perturbation theory off of the background metric. We derive an equation for the long-wavelength part of the leading order deviation of the metric from the background metric, which contains the usual terms occurring in linearized perturbation theory plus additional contributions from the small-scale inhomogeneities. Under various assumptions concerning the absence of gravitational radiation and the nonrelativistic behavior of the matter, we argue that the short-wavelength deviations of the metric from the background metric near a point $x$ should be accurately described by Newtonian gravity, taking into account only the matter lying within a homogeneity length scale of $x$. Finally, we argue that our framework should provide an accurate description of the actual universe.

We discuss aspects of global and gauged symmetries in quantum field theory and quantum gravity, focusing on discrete gauge symmetries. An effective Lagrangian description of ${\mathbb{Z}}_p$ gauge theories shows that they are associated with an emergent ${\mathbb{Z}}_p$ 1-form (Kalb-Ramond) gauge symmetry. This understanding leads us to uncover new observables and new phenomena in nonlinear $\sigma$ models. It also allows us to expand on Polchinski’s classification of cosmic strings. We argue that in models of quantum gravity, there are no global symmetries, all continuous gauge symmetries are compact, and all charges allowed by Dirac quantization are present in the spectrum. These conjectures are not new, but we present them from a streamlined and unified perspective. Finally, our discussion about string charges and symmetries leads to a more physical and more complete understanding of recently found consistency conditions of supergravity.

We consider point particles with arbitrary energy per unit mass $E$ that fall radially into a higher-dimensional, nonrotating, asymptotically flat black hole. We compute the energy and linear momentum radiated in this process as functions of $E$ and of the spacetime dimensionality $D=n+2$ for $n=2,\dots ,9$ (in some cases we go up to 11). We find that the total energy radiated increases with $n$ for particles falling from rest ($E=1$). For fixed particle energies $1<E\le 2$ we show explicitly that the radiation has a local minimum at some critical value of $n$, and then it increases with $n$. We conjecture that such a minimum exists also for higher particle energies. The present point-particle calculation breaks down when $n=11$, because then the radiated energy becomes larger than the particle mass. Quite interestingly, for $n=11$ the radiated energy predicted by our calculation would also violate Hawking’s area bound. This hints at a qualitative change in gravitational radiation emission for $n\gtrsim 11$. Our results are in very good agreement with numerical simulations of low-energy, unequal-mass black hole collisions in $D=5$ (that will be reported elsewhere) and they are a useful benchmark for future nonlinear evolutions of the higher-dimensional Einstein equations.

We define a set of boundary conditions that ensure the presence of a null hypersurface with the essential characteristics of a horizon, using the formalism of weakly isolated horizons as a guide. We then determine the diffeomorphisms that preserve these boundary conditions, and derive a dynamical action for these diffeomorphisms in a neighborhood of the horizon. The action is similar to that of the Liouville theory, and the equation of motion of the gravitational degrees of freedom approaches that of a free two-dimensional conformal field in the near-horizon region.

We present a generic framework, baryomorphosis, which modifies the baryon asymmetry to be naturally of the order of a typical thermal relic weakly interacting massive particle (WIMP) density. We consider a simple scalar-based model to show how this is possible. This model introduces a sector in which a large initial baryon asymmetry is injected into particles (”annihilons”), ${\varphi }_B$, ${\widehat{\varphi }}_B$, of mass $\sim 100\mathrm{GeV}–1\mathrm{TeV}$. ${\varphi }_B{\widehat{\varphi }}_B$ annihilations convert the initial ${\varphi }_B$, ${\widehat{\varphi }}_B$ asymmetry to a final asymmetry with a thermal relic WIMP-like density. This subsequently decays to a conventional baryon asymmetry whose magnitude is naturally related to the density of thermal relic WIMP dark matter. In this way the two coincidences of baryons and dark matter, i.e. why their densities are similar to each other and why they are both similar to a WIMP thermal relic density (the “WIMP miracle”), may be understood. The model may be tested by the production of annihilons at colliders.

Standard big-bang nucleosynthesis (BBN) predicts only a trace abundance of lithium and no heavier elements, but some alternatives predict a nonzero primordial metallicity. Here we explore whether CMB measurements may set useful constraints to the primordial metallicity and/or whether the standard CMB calculations are robust, within the tolerance of forthcoming CMB maps, to the possibility of primordial metals. Metals would affect the recombination history (and thus CMB power spectra) in three ways: (1) $\mathrm{Ly}\alpha$ photons can be removed (and recombination thus accelerated) by photoionizing metals; (2) The Bowen resonance-fluorescence mechanism may degrade $\mathrm{Ly}\beta$ photons and thus enhance the $\mathrm{Ly}\beta$ escape probability and speed up recombination; (3) Metals could affect the low-redshift tail of the CMB visibility function by providing additional free electrons. The last two of these provide the strongest CMB signal. However, the effects are detectable in the Planck satellite only if the primordial metal abundance is at least a few hundredths of solar for (2) and a few tenths of solar for (3). We thus conclude that Planck will not be able to improve upon current constraints to primordial metallicity, at the level of a thousandth of solar, from the Lyman-$\alpha$ forest and ultra-metal-poor halo stars, and that the CMB power-spectrum predictions for Planck suffer no uncertainty arising from the possibility that there may be primordial metals.

A set of once subtracted dispersion relations with imposed crossing symmetry condition for the $\pi \pi$ $D$- and $F$-wave amplitudes is derived and analyzed. An example of numerical calculations in the effective two-pion mass range from the threshold to 1.1 GeV is presented. It is shown that these new dispersion relations impose quite strong constraints on the analyzed $\pi \pi$ interactions and are very useful tools to test the $\pi \pi$ amplitudes. One of the goals of this work is to provide a complete set of equations required for easy use. Full analytical expressions are presented. Along with the well-known dispersion relations successful in testing the $\pi \pi$ $S$- and $P$-wave amplitudes, those presented here for the $D$ and $F$ waves give a complete set of tools for analyses of the $\pi \pi$ interactions.

We study the impact of minimal nonsupersymmetric models of resonant leptogenesis on charged-lepton flavor violation and the neutrino-mixing angle ${\theta }_{13}$. Possible low-scale flavor realizations of resonant $\tau$-, $\mu$- and $e$-leptogenesis provide very distinct and predictive frameworks to explain the observed baryon asymmetry in the Universe by sphaleron conversion of an individual $\tau$-, $\mu$- and $e$-lepton-number asymmetry which gets resonantly enhanced via out-of-equilibrium decays of nearly degenerate heavy Majorana neutrinos. Based on approximate flavor symmetries, we construct viable scenarios of resonant $\tau$-, $\mu$- and $e$-leptogenesis compatible with universal right-handed neutrino masses at the grand unified theory scale, where the required heavy-neutrino mass splittings are generated radiatively. The heavy Majorana neutrinos in such scenarios can be as light as 100 GeV and their couplings to two of the charged leptons may be large. In particular, we explicitly demonstrate the compelling role that the three heavy Majorana neutrinos play, in order to obtain successful leptogenesis and experimentally testable rates for lepton-flavor violating processes, such as $\mu \to e\gamma$ and $\mu \to e$ conversion in nuclei.

A new approach to building models of generalized parton distributions (GPDs) is discussed that is based on the factorized DD (double distribution) ansatz within the single-DD formalism. The latter was not used before, because reconstructing GPDs from the forward limit one should start in this case with a very singular function $f(\beta )/\beta$ rather than with the usual parton density $f(\beta )$. This results in a nonintegrable singularity at $\beta =0$ exaggerated by the fact that $f(\beta )$’s, on their own, have a singular ${\beta }^{-a}$ Regge behavior for small $\beta$. It is shown that the singularity is regulated within the GPD model of Szczepaniak et al., in which the Regge behavior is implanted through a subtracted dispersion relation for the hadron-parton scattering amplitude. It is demonstrated that using proper softening of the quark-hadron vertices in the regions of large parton virtualities results in model GPDs $H(x,\xi )$ that are finite and continuous at the “border point” $x=\xi$. Using a simple input forward distribution, we illustrate implementation of the new approach for explicit construction of model GPDs. As a further development, a more general method of regulating the $\beta =0$ singularities is proposed that is based on the separation of the initial single DD $f(\beta ,\alpha )$ into the “plus” part $[f(\beta ,\alpha ){]}_{+}$ and the $D$ term. It is demonstrated that the “DD+D” separation method allows one to (re)derive GPD sum rules that relate the difference between the forward distribution $f(x)=H(x,0)$ and the border function $H(x,x)$ with the $D$-term function $D(\alpha )$.

We analyze quark condensates and chiral (scalar) susceptibilities including isospin-breaking effects at finite temperature $T$. These include $m_u\ne m_d$ contributions as well as electromagnetic ($e\ne 0$) corrections, both treated in a consistent chiral Lagrangian framework to leading order in $SU(2)$ and $SU(3)$ chiral perturbation theory, so that our predictions are model-independent. The chiral restoration temperature extracted from $⟨\overline{q}q⟩=⟨\overline{u}u+\overline{d}d⟩$ is almost unaffected, while the isospin-breaking order parameter $⟨\overline{u}u-\overline{d}d⟩$ grows with $T$ for the three-flavor case $SU(3)$. We derive a sum rule relating the condensate ratio $⟨\overline{q}q⟩(e\ne 0)/⟨\overline{q}q⟩(e=0)$ with the scalar susceptibility difference $\chi (T)-\chi (0)$, directly measurable on the lattice. This sum rule is useful also for estimating condensate errors in staggered lattice analysis. Keeping $m_u\ne m_d$ allows one to obtain the connected and disconnected contributions to the susceptibility, even in the isospin limit, whose temperature, mass, and isospin-breaking dependence we analyze in detail. The disconnected part grows linearly, diverging in the chiral (infrared) limit as $T/M_{\pi }$, while the connected part shows a quadratic behavior, infrared regular as $T^2/M_{\eta }^2$, and coming from ${\pi }^0\eta$ mixing terms. This smooth connected behavior suggests that isospin-breaking correlations are weaker than critical chiral ones near the transition temperature. We explore some consequences in connection with lattice data and their scaling properties, for which our present analysis for physical masses, i.e. beyond the chiral limit, provides a useful model-independent description for low and moderate temperatures.

We study a distinct supersymmetric signal of multiphotons in association with jets and missing transverse energy. At least one of these photons has the origin in displaced vertex, and thus it is delayed and nonpointing. We consider a supersymmetric scenario in which the gravitino is the lightest supersymmetric particle (LSP) (with a mass $\sim 1\mathrm{keV}$) and the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP). The NLSP decays dominantly into a photon and a gravitino within the detector with a decay length ranging from $c{\tau }_{\tilde{\chi }}\sim 50–100\mathrm{cm}$. In addition, we assume that the second-lightest neutralino and the lightest neutralino are nearly degenerate and this leads to a prompt radiative decay of the next-to-lightest neutralino into a photon and a lightest neutralino with a large branching ratio. Such degenerate neutralinos can be realized in various representations of the $SU(5)$, $SO(10)$ and $E(6)$ GUT group. The nonpointing photons can be reconstructed at the electromagnetic calorimeter of the ATLAS detector, which have been designed with good timing and directional resolution. We find that with a center-of-mass energy $E_{\mathrm{cm}}=14\mathrm{TeV}$ at an integrated luminosity of $100{\mathrm{fb}}^{-1}$ one may see evidence of hundreds of triphoton events at the LHC, in addition to several thousands diphoton events. We also predict the event rates even at the early phase of LHC run.