Motivated by anomalies in cosmic ray observations and by attempts to solve questions of the Standard Model of particle physics like the $(g-2{)}_{\mu }$ discrepancy, $U(1)$ extensions of the Standard Model have been proposed in recent years. Such $U(1)$ extensions allow for the interaction of dark matter by exchange of a photonlike massive force carrier ${\gamma }^{\prime }$ not included in the Standard Model. In order to search for ${\gamma }^{\prime }$ bosons, various experimental programs have been started. One approach is the dedicated search at fixed-target experiments at modest energies as performed at microtron (MAMI) or at the Jefferson Lab. In these experiments the process $e(A,Z)\to e(A,Z)l^{+}{l}^{-}$ is investigated, and a search for a very narrow resonance in the invariant mass distribution of the $l^{+}{l}^{-}$ pair is performed. In this work we analyze this process in terms of signal and background in order to describe existing data obtained by the A1 experiment at MAMI with the aim to give accurate predictions for exclusion limits in the ${\gamma }^{\prime }$ parameter space. We present a detailed theoretical analysis of the cross sections entering in the description of such processes.

The space-time reduced model of large $N$ QCD with two adjoint Wilson fermions is constructed by applying the symmetric twist boundary conditions with nonvanishing flux $k$. For large but finite $N=L^2$, the model should behave as the large $N$ version of the ordinary lattice gauge model on a $V=L^4$ space-time volume. We perform a comparison of the $N$ dependence of several quantities in this model and in the $k=0$ model (corresponding to periodic boundary conditions). Although the ${\mathrm{Z}}^4(N)$ symmetry seems unbroken in all cases, the $N$-dependence analysis favors the use of the same values of $k$ and $L$ for which the symmetry is also unbroken in the pure gauge case. In particular, the $k=0$ model, studied recently by several authors, shows a large and irregular dependence on $N$ within our region of parameters. This makes this reduced model very impractical for extracting physical information about the large $N$ lattice theory. On the contrary, the model for $N=289={17}^2$ and large enough $k$ gives consistent results, even for extended observables as Wilson loops $W(R,T)$ up to $R$, $T=8$, matching the expected behavior for the lattice model with a ${17}^4$ space-time volume.

The isospin violating $J/\Psi \to \varphi {\pi }^0\eta$ decay is thought to be dominated by the mixing of the $f_0(980)$ and $a_0(980)$ scalar resonances. We make a theoretical evaluation of the $J/\Psi \to \varphi {\pi }^0\eta$ decay extending our own previous model for other $J/\Psi$ decays into one vector meson and two pseudoscalars using the techniques of the chiral unitary approach. The scalar resonances are dynamically generated through the final-state interaction of the pseudoscalar mesons implementing unitarity from the lowest order chiral perturbation theory amplitudes. Besides the direct $J/\Psi \varphi PP$ vertex, other mechanisms like the sequential exchange of vector and axial-vector mesons are shown to be important in order to obtain the actual strength of the mixing. We get a very good agreement with the ${\pi }^0\eta$ invariant mass distribution and branching ratio with recent BESIII data. Quantification of the $f_0(980)-a_0(980)$ mixing is done and compared with results from several experiments.

We investigate a new sequential recombination algorithm which effectively subtracts background as it reconstructs the jet. We examine the new algorithm’s behavior in light of existing algorithms, and we find that in Monte Carlo comparisons, the new algorithm’s robustness against collision backgrounds is comparable to that of other jet algorithms when the latter have been augmented by further background subtraction techniques.

The $\gamma Z$-box diagram for parity violating elastic $e\mathrm{\text{−}}p$ scattering has recently undergone a thorough analysis by several research groups. Though all now agree on the analytic form of the diagram, the numerical results differ due to the treatment of the structure functions, $F_{1,2,3}^{\gamma Z}(x,{\mathcal{Q}}^2)$. Currently, $F_{1,2,3}^{\gamma Z}(x,{\mathcal{Q}}^2)$ at low ${\mathcal{Q}}^2$ and $W^2$ must be approximated through the modification of existing fits to electromagnetic structure function data. We motivate and describe the modification used to obtain $F_{1,2}^{\gamma Z}(x,{\mathcal{Q}}^2)$ in our previous work. We also describe an alternative modification and compare the result to our original calculation. Finally, we present a new modification procedure to acquire $F_3^{\gamma Z}(x,{\mathcal{Q}}^2)$ in the resonance region and calculate the axial contribution to the $\gamma Z$-box diagram. Details of these modifications will illuminate where discrepancies between the groups arise and where future improvements can be made.

We present a search for anomalous components of the quartic gauge boson coupling $WW\gamma \gamma$ in events with an electron, a positron and missing transverse energy. The analyzed data correspond to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 detector in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The presence of anomalous quartic gauge couplings would manifest itself as an excess of boosted $WW$ events. No such excess is found in the data, and we set the most stringent limits to date on the anomalous coupling parameters $a_0^W$ and $a_C^W$. When a form factor with ${\Lambda }_{\mathrm{cutoff}}=0.5\mathrm{TeV}$ is used, the observed upper limits at 95% C.L. are $|a_0^W/{\Lambda }^2|<0.0025{\mathrm{GeV}}^{-2}$ and $|a_C^W/{\Lambda }^2|<0.0092{\mathrm{GeV}}^{-2}$.

Recently, Bañados, Silk, and West analyzed a collision of two particles near the horizon of the extremal Kerr black hole and demonstrated that the energy in the center-of-mass frame can be arbitrarily large provided the angular momentum of one of the colliding particles takes a special value. As is known, the vicinity of the extremal Kerr black hole horizon can be viewed as a complete vacuum spacetime in its own right. In this work, we consider a collision of two neutral particles within the context of the near horizon extremal Kerr geometry and demonstrate that the energy in the center-of-mass frame is finite for any admissible value of the particle parameters. An explanation of why the two approaches disagree on the Bañados-Silk-West effect is given.

We demonstrate a bijection between reparametrization invariant effective actions for relativistic $p$-branes in flat target space and effective actions for transverse brane perturbations with nonlinearly realized Poincaré symmetry. Starting with an action with nonlinearly realized symmetry, we construct the corresponding reparametrization invariant action by introducing Stückelberg fields. They combine with the transverse modes to form a Lorentz vector. The manifest Lorentz symmetry of the reparametrization invariant action follows directly from the nonlinearly realized Lorentz symmetry of the initial action in terms of the physical modes.

We discuss how the $1/N_c$ expansion and the chiral random matrix theory ($\chi \mathrm{RMT}$) can be used in the study of large-$N_c$ gauge theories. We first clarify the parameter region in which each of these two approaches is valid. While the fermion mass $m$ is fixed in the standard large-$N_c$ arguments (’t Hooft large-$N_c$ limit), $m$ must be scaled appropriately with a certain negative power of $N_c$ in order for the gauge theories to be described by the $\chi \mathrm{RMT}$. Then, although these two limits are not compatible in general, we show that the breakdown of chiral symmetry can be detected by combining the large-$N_c$ argument and the $\chi \mathrm{RMT}$ with some care. As a concrete example, we numerically study the four-dimensional $SU(N_c)$ gauge theory with $N_f=2$ heavy adjoint fermions, introduced as the center symmetry preserver keeping the infrared physics intact, on a $2^4$ lattice. By looking at the low-lying eigenvalues of the overlap-Dirac operator for a massless probe fermion in the adjoint representation, we find that the chiral symmetry is indeed broken with the expected breaking pattern. This result reproduces a well-known fact that the chiral symmetry is spontaneously broken in the pure $SU(N_c)$ gauge theory in the large-$N_c$ and the large-volume limit and therefore supports the validity of the combined approach. We also provide an interpretation of the gap and unexpected $N_c$ scaling, both of which are observed in the Dirac spectrum.

The most general formulation of Penrose’s inequality yields a lower bound for Arnowitt-Deser-Misner mass in terms of the area, charge, and angular momentum of black holes. This inequality is in turn equivalent to an upper and lower bound for the area in terms of the remaining quantities. In this paper, we establish the lower bound for a single black hole in the setting of axisymmetric maximal initial data sets for the Einstein-Maxwell equations, when the non-electromagnetic matter fields are not charged and satisfy the dominant energy condition. It is shown that the inequality is saturated if and only if the initial data arise from the extreme Kerr-Newman spacetime. Further refinements are given when either charge or angular momentum vanish. Last, we discuss the validity of the lower bound in the presence of multiple black holes.

Shape dynamics is a theory of gravity that waives refoliation invariance in favor of spatial Weyl invariance. It is a canonical theory, constructed from a Hamiltonian, $3+1$ perspective. One of the main deficits of shape dynamics is that its Hamiltonian is only implicitly constructed as a functional of the phase space variables. In this paper, I write down the equations of motion for shape dynamics to show that over a curve in phase space representing a Minkowski space-time, shape dynamics possesses Poincaré symmetry for appropriate boundary conditions. The proper treatment of such boundary conditions leads us to completely formulate shape dynamics for open manifolds in the asymptotically flat case. We study the charges arising in this case and find a new definition of total energy, which is completely invariant under spatial Weyl transformations close to the boundary. We then use the equations of motion once again to find a nontrivial solution of shape dynamics, consisting of a flat static Universe with a pointlike mass at the center. We calculate its energy through the new formula and rederive the usual Schwarzschild mass.

We consider orbital-tidal coupling in a binary stellar system to first-post-Newtonian (1PN) order. We derive the orbital equations of motion for bodies with spins and mass quadrupole moments and show that they conserve the total linear momentum of the binary. We note that spin-orbit coupling must be included in a 1PN treatment of tidal interactions in order to maintain consistency (except in the special case of adiabatically induced quadrupoles): the inclusion of 1PN quadrupolar tidal effects while omitting spin effects would lead to a failure of momentum conservation for generic evolution of the quadrupoles. We use momentum conservation to specialize our analysis to the system’s center-of-mass-energy frame; we find the binary’s relative equation of motion in this frame and also present a generalized Lagrangian from which it can be derived. We then specialize to the case in which the quadrupole moment is adiabatically induced by the tidal field (in which case it is consistent to ignore spin effects). We show how the adiabatic dynamics for the quadrupole can be incorporated into our action principle and present the simplified orbital equations of motion and conserved energy for the adiabatic case. These results are relevant to the gravitational-wave signal of inspiralling binary neutron stars.

In this paper we consider a cosmological model whose main components are a scalar field and a generalized Chaplygin gas. We obtain an exact solution for a flat arbitrary potential. This solution have the right dust limit when the Chaplygin parameter $A\to 0$. We use the dynamical systems approach in order to describe the cosmological evolution of the mixture for an exponential self-interacting scalar field potential. We study the scalar field with an arbitrary self-interacting potential using the “Method of $f$-devisers.” Our results are illustrated for the special case of a coshlike potential. We obtain that the usual scalar-field-dominated and scaling solutions cannot be late- time attractors in the presence of the Chaplygin gas (with $\alpha >0$). We recover the standard results at the dust limit ($A\to 0$). In particular, for the exponential potential, the late-time attractor is a pure generalized Chaplygin solution mimicking an effective cosmological constant. In the case of arbitrary potentials, the late-time attractors are de Sitter solutions in the form of a cosmological constant, a pure generalized Chaplygin solution or a continuum of solutions, when the scalar field and the Chaplygin gas densities are of the same orders of magnitude. The different situations depend on the parameter choices.

The usual account for the origin of cosmic structure during inflation is not fully satisfactory, as it lacks a physical mechanism capable of generating the inhomogeneity and anisotropy of our Universe, from an exactly homogeneous and isotropic initial state associated with the early inflationary regime. The proposal in [A. Perez, H. Sahlmann, and D. Sudarsky, Classical Quantum Gravity 23, 2317 (2006)] considers the spontaneous dynamical collapse of the wave function as a possible answer to that problem. In this work, we review briefly the difficulties facing the standard approach, as well as the answers provided by the above proposal and explore their relevance to the investigations concerning the characterization of the primordial spectrum and other statistical aspects of the cosmic microwave background and large-scale matter distribution. We will see that the new approach leads to novel ways of considering some of the relevant questions, and, in particular, to distinct characterizations of the non-Gaussianities that might have left imprints on the available data.

The comparison between dynamical mass and lensing mass provides a targeted test for a wide range of modified gravity models. In our previous paper Lam et al. [Phys. Rev. Lett. 109, 051301 (2012)] we showed, through numerical simulations, that the measurement of the line-of-sight velocity dispersion around stacked massive clusters whose lensing masses are known allows for stringent constraints on modified gravity on scales of $2–15h^{-1}\mathrm{Mpc}$. In this work we develop a semianalytical approach based on the halo model to describe the phase-space distribution and the line-of-sight velocity dispersion for different tracers. The model distinguishes contributions from the halo pairwise velocity and the virial velocity within halos. We also discuss observational complications, in particular the contribution from Hubble flow, and show how our model can incorporate these complications. We then incorporate the effects of modified gravity [specifically, $f(R)$ and braneworld models], and show that the model predictions are in excellent agreement with modified gravity simulations. More broadly, the phase-space distribution provides a sensitive test of our understanding of hierarchical structure formation when confronted with observations via this model.

We present a new derivation of the conservative form of the general relativistic Boltzmann equation and specialize it to the $3+1$ metric. The resulting transport equation is intended for use in simulations involving numerical relativity, particularly in the absence of spherical symmetry. The independent variables are lab frame coordinate basis spacetime position components and comoving frame curvilinear momentum space coordinates. With an eye toward astrophysical applications—such as core-collapse supernovae and compact object mergers—in which the fluid includes nuclei and/or nuclear matter at finite temperature and in which the transported particles are neutrinos, we examine the relationship between lepton number and four-momentum exchange between neutrinos and the fluid.

In this work we investigate the exclusive photoproduction of $J/\psi$ and the radially excited $\psi (2S)$ state off nucleons in proton-proton collisions. The theoretical framework considered in the analysis is the light-cone dipole formalism and predictions are done for proton-proton collisions at the CERN-LHC energy of 7 TeV. The theoretical uncertainties are investigated and a comparison is made to the recent LHCb Collaboration data for the exclusive charmonium production.

To explain all the available experimental results, we have proposed the electroweak supersymmetry (EWSUSY) previously, where the squarks and/or gluino are heavy around a few TeVs while the sleptons, sneutrinos, bino, winos, and/or Higgsinos are light within 1 TeV. In the next to minimal supersymmetric Standard Model, we perform the systematic ${\chi }^2$ analyses on parameter space scan for three EWSUSY scenarios: (I) $R$-parity conservation and one dark matter candidate, (II) $R$-parity conservation and multicomponent dark matter, (III) $R$-parity violation. We obtain the minimal ${\chi }^2/(\mathrm{\text{degree of freedom}})$ of $10.2/15$, $9.6/14$, and $9.2/14$ respectively for scenarios I, II, and III. Considering the constraints from the LHC neutralino/chargino and slepton searches, we find that the majority of viable parameter space preferred by the muon anomalous magnetic moment has been excluded except for the parameter space with moderate to large $\tan \beta (\gtrsim 8)$. Especially, the most favorable parameter space has relatively large $\tan \beta$, moderate $\lambda$, small ${\mu }_{\mathrm{eff}}$, heavy squarks/gluino, and the second lightest $CP$-even neutral Higgs boson with mass around 125 GeV. In addition, if the left-handed smuon is nearly degenerate with or heavier than wino, there is no definite bound on wino mass. Otherwise, the wino with mass up to $\sim 450\mathrm{GeV}$ has been excluded. Furthermore, we present several benchmark points for scenarios I and II, and briefly discuss the prospects of the EWSUSY searches at the 14 TeV LHC and ILC.

We investigate the radiative process of ${\Lambda }_b\to \Lambda \gamma$ in the standard model as well as models with one or two compact universal extra dimensions. Using the form factors entered to the low-energy matrix elements, calculated via light-cone QCD in full theory, we calculate the total decay width and branching ratio of this decay channel. We compare the results of the extra-dimensional models with those of the standard model on the considered physical quantities and look for the deviations of the results from the standard model predictions at different values of the compactification scale ($1/R$).

For $B_{d,s}\to {\pi }^{\mp }{K}^{\pm }$ and $K^{(*)}{K}^{(*)}$ decays, the flavor symmetry-breaking effects may be particularly small since the final-state interactions should be the same between the corresponding $B_d$ and $B_s$ decays due to the charge conjugation symmetry of the final states. This is consistent with the newly measured direct $CP$ asymmetry of $B_s\to {\pi }^{+}{K}^{-}$. These decays are thus supposed to be important in testing the Standard Model and in probing new physics effects. However, the observation of pure annihilation decay $B_s\to {\pi }^{+}{\pi }^{-}$ appears to imply a large annihilation scenario with ${\rho }_A\sim 3$, in contrast to the case of ${\rho }_A\sim 1$ in $B_{u,d}$ decays in the framework of QCD factorization. This seems to indicate unexpectedly large flavor symmetry-breaking effects between the annihilation amplitudes of $B_s$ and $B_{u,d}$ decays. This apparent contradiction could be resolved by noticing that there is a priori no reason to justify the common practice of assuming the universality of annihilation parameters for different Dirac structures of effective operators. We then argue that, for $B_{d,s}\to {\pi }^{\mp }{K}^{\pm }$ decays, the flavor symmetry-breaking effects of annihilation amplitudes have all been included in the initial-state decay constants and are thus small. But the flavor symmetry-breaking effects in $B_{d,s}\to K^{(*)}{K}^{(*)}$ decays are likely to be much larger, as part of the annihilation topologies of $B_s\to KK$ decay could be related to $B_s\to {\pi }^{+}{\pi }^{-}$ decay. Therefore when new physics effects are searched for in these decay channels, care must be taken to consider the potentially large flavor symmetry-breaking effects in more detail.