In this paper, we discuss the systematics of quarkonium production at the LHC. In particular, we focus on the necessity to sum logs of the form $\log (Q/p_{\perp })$ and $\log (p_{\perp }/m_Q)$. We show that the former contributions are power suppressed, while the latter, whose contribution in fragmentation is well known, also arise in the short distance (i.e., nonfragmentation) production mechanisms. Though these contributions are suppressed by powers of $m_Q/p_{\perp }$, they can be enhanced by inverse powers of $v$, the relative velocity between heavy quarks in the quarkonium. In the limit $p_{\perp }\gg m_Q$, short-distance production can be thought of as the fragmentation of a pair of partons (i.e., the heavy quark and antiquark) into the final state quarkonium. We derive an all-order factorization theorem for this process in terms of double parton fragmentation functions and calculate the one-loop anomalous dimension matrix for the double parton fragmentation functions.

Recently a new state of the $b\overline{b}$ system has been observed by the ATLAS Collaboration, with a mass of $10530\pm 5\pm 9\mathrm{MeV}$. This state has been identified with the $n=3$ $P$-wave radial excitations of the $b\overline{b}$ system with parallel quark spins, called ${\chi }_b(3P)$. The measured value of the mass corresponds to the average of the $J=0$, 1, and 2 states, while the splittings of these states are not yet resolved. In this work we present predictions from different potentials models for the values of these splittings.

We note that a simple two parameter description of lepton mixing is possible, which reproduces the features that apparently emerge from global fits at the $1\sigma$ level: if $U_{e3}$ is nonzero, it implies that the solar neutrino mixing parameter ${sin}^2{\theta }_{12}$ is less than $1/3$ by order $|U_{e3}{|}^2$. If the $CP$ phase $\delta$ is around $\pi$, it implies that the atmospheric neutrino mixing parameter ${sin}^2{\theta }_{23}$ is less than $1/2$ by order $|U_{e3}|$. The mixing scheme can be described by a 23-rotation appearing to the right of a tri-bimaximal mixing matrix. We quantify the excellent agreement of the scheme with data statistically, and comment on model building aspects.

Upcoming fixed-target experiments designed to search for new sub-GeV forces will also have sensitivity to the never before observed true muonium atom, a bound state of ${\mu }^{+}{\mu }^{-}$. We describe the production and decay characteristics of true muonium relevant to these experiments. Importantly, we find that secondary production mechanisms dominate over primary production for the long-lived 2S and 2P states, leading to total yields an order of magnitude larger than naive estimates previously suggested. We present yield estimates for true muonium as a function of energy fraction and decay length, useful for guiding future experimental studies. Discovery and measurement prospects appear very favorable.

We obtain constraints on three universal extra-dimensional models utilizing limits from the CMS Collaboration on $W^{\prime }$ production and decay into a single-top-quark final state. We find a weak constraint on the minimal universal extra-dimensional model due to small Kaluza-Klein number violating terms. In contrast, the $W^{\prime }$ search puts a strong limit on the size of the Dirac mass term of the quarks in split universal extra-dimension models. In nonminimal universal extra-dimension models, the $W^{\prime }$ search constrains the splitting between the boundary-localized kinetic terms of the gauge bosons and the quarks. Each of these bounds can be translated into constraints on the mass splitting between the Kaluza-Klein excitations of the $SU(2)$ charged quarks and the Klauza-Klein excitations of the $W$ boson.

We report a study of the process $\gamma \gamma \to X\to {\eta }_c{\pi }^{+}{\pi }^{-}$, where $X$ stands for one of the resonances ${\chi }_{c2}(1P)$, ${\eta }_c(2S)$, $X(3872)$, $X(3915)$, or ${\chi }_{c2}(2P)$. The analysis is performed with a data sample of $473.9{\mathrm{fb}}^{-1}$ collected with the BABAR detector at the PEP-II asymmetric-energy electron-positron collider. We do not observe a significant signal for any channel, and calculate 90% confidence-level upper limits on the products of branching fractions and two-photon widths ${\Gamma }_{X\to \gamma \gamma }\mathcal{B}(X\to {\eta }_c{\pi }^{+}{\pi }^{-})$: 15.7 eV for ${\chi }_{c2}(1P)$, 133 eV for ${\eta }_c(2S)$, 11.1 eV for $X(3872)$ (assuming it to be a spin-2 state), 16 eV for $X(3915)$ (assuming it to be a spin-2 state), and 18 eV for ${\chi }_{c2}(2P)$. We also report upper limits on the ratios of branching fractions $\mathcal{B}({\eta }_c(2S)\to {\eta }_c{\pi }^{+}{\pi }^{-})/\mathcal{B}({\eta }_c(2S)\to K_S^0{K}^{+}{\pi }^{-})<10.0$ and $\mathcal{B}({\chi }_{c2}(1P)\to {\eta }_c{\pi }^{+}{\pi }^{-})/\mathcal{B}({\chi }_{c2}(1P)\to K_S^0{K}^{+}{\pi }^{-})<32.9$ at the 90% confidence level.

The combination of searches performed by the CDF and D0 collaborations at the Fermilab Tevatron Collider for neutral Higgs bosons produced in association with $b$ quarks is reported. The data, corresponding to $2.6{\mathrm{fb}}^{-1}$ of integrated luminosity at CDF and $5.2{\mathrm{fb}}^{-1}$ at D0, have been collected in final states containing three or more $b$ jets. Upper limits are set on the cross section multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson. Significant enhancements to the production of Higgs bosons can be found in theories beyond the standard model, for example, in supersymmetry. The results are interpreted as upper limits in the parameter space of the minimal supersymmetric standard model in a benchmark scenario favoring this decay mode.

We consider $p$-branes with one or more circular directions fibered over the transverse space. The fibration, in conjunction with the transverse space having a blown-up cycle, enables these $p$-brane solutions to be completely regular. Some such circularly wrapped D3-brane solutions describe flows from $SU(N{)}^3$ $\mathcal{N}=2$ theory, ${\mathbb{F}}_0$ theory, as well as an infinite family of superconformal quiver gauge theories, down to three-dimensional field theories. We discuss the operators that are turned on away from the UV fixed points. Similarly, there are wrapped M2-brane solutions which describe smooth flows from known three-dimensional supersymmetric Chern-Simons matter theories, such as Aharony-Bergman-Jafferis-Maldacena theory. We also consider $p$-brane solutions on gravitational instantons, and discuss various ways in which $U$-duality can be applied to yield other nonsingular solutions.

We perform a global renormalization group study of $O(N)$ symmetric Wess-Zumino theories and their phases in three Euclidean dimensions. At infinite $N$ the theory is solved exactly. The phases and phase transitions are worked out for finite and infinite short-distance cutoffs. A distinctive new feature arises at strong coupling, where the effective superfield potential becomes multivalued, signalled by divergences in the fermion-boson interaction. Our findings resolve the long-standing puzzle about the occurrence of degenerate $O(N)$ symmetric phases. At finite $N$, we find a strongly coupled fixed point in the local potential approximation and explain its impact on the phase transition. We also examine the possibility for a supersymmetric Bardeen-Moshe-Bander phenomenon and relate our findings with the spontaneous breaking of supersymmetry in other models.

Recently, a novel idea about our expanding Universe was proposed by T. Padmanabhan [arXiv:1206.4916]. He suggested that the expansion of our Universe can be thought of as the emergence of space as cosmic time progresses. The emergence is governed by the basic relation that the increase rate of Hubble volume is linearly determined by the difference between the number of degrees of freedom on the horizon surface and the one in the bulk. In this paper, following this idea, we generalize the basic relation to derive the Friedmann equations of an ($n+1$)-dimensional Friedmann-Robertson-Walker universe corresponding to general relativity, Gauss-Bonnet gravity, and Lovelock gravity.

We consider singularity theorems in asymptotically anti–de Sitter (AdS) spacetimes. In the first part, we discuss the global methods used to show geodesic incompleteness and see that when the conditions imposed in Hawking and Penrose’s singularity theorem are satisfied, a singularity must appear in asymptotically AdS spacetime. The recent observations of turbulent instability of asymptotically AdS spacetimes indicate that AdS spacetimes are generically singular even if a closed trapped surface, which is one of the main conditions of the Hawking and Penrose theorem, does not exist in the initial hypersurface. This may lead one to expect to obtain a singularity theorem without imposing the existence of a trapped set in asymptotically AdS spacetimes. This, however, does not appear to be the case. We consider, within the use of global methods, two such attempts and discuss difficulties in eliminating conditions concerning a trapped set from singularity theorems in asymptotically AdS spacetimes. Then in the second part, we restrict our attention to the specific case of spherically symmetric, perfect fluid systems in asymptotically AdS spacetime, and show that under a certain condition concerning dynamics of the fluid, a closed trapped surface must form, and as a combined result with Hawking and Penrose’s theorem, that such a spacetime must be singular.

Einstein-Gauss-Bonnet gravity provides a natural higher dimensional and higher order curvature generalization of Einstein gravity. It contains a new, presumably microscopic, length scale that should affect short distance properties of the dynamics, such as Choptuik scaling. We present the results of a numerical analysis in generalized flat slice coordinates of self-gravitating massless scalar spherical collapse in five and six dimensional Einstein-Gauss-Bonnet gravity near the threshold of black hole formation. Remarkably, the behavior is universal (i.e., independent of initial data) but qualitatively different in five and six dimensions. In five dimensions there is a minimum horizon radius, suggestive of a first order transition between black hole and dispersive initial data. In six dimensions no radius gap is evident. Instead, below the Gauss-Bonnet scale there is a change in the critical exponent and echoing period.

We study the formation and perturbation of black holes by null fluxes of neutral matter in a quadratic extension of general relativity formulated à la Palatini. Working in a spherically symmetric space-time, we obtain an exact analytical solution for the metric that extends the usual Vaidya-type solution to this type of theory. We find that the resulting space-time is formally that of a Reissner-Nordström black hole but with an effective charge term carrying the wrong sign in front of it. This effective charge is directly related to the luminosity function of the radiation stream. When the ingoing flux vanishes, the charge term disappears and the space-time relaxes to that of a Schwarzschild black hole. We provide two examples that illustrate the formation of a black hole from Minkowski space and the perturbation by a finite pulse of radiation of an existing Schwarzschild black hole.

In this work, we further investigate the family of $f(R)$ dark energy models that can exactly mimic the same background expansion history as that of the $\Lambda \mathrm{CDM}$ model. We study the large scale structure in the $f(R)$ gravity using the full set cosmological perturbation equations. We investigate the structure formation in both the spatially flat and curved universe. We also confront our model with the latest observations and conduct a Markov chain Monte Carlo analysis on the parameter space.

With the goal in mind of deriving a method to compute quantum corrections for the real-time evolution in quantum field theory, we analyze the problem from the perspective of the Wigner function. We argue that this provides the most natural way to justify and extend the classical approximation. A simple proposal is presented that can allow us to give systematic quantum corrections to the evolution of expectation values and/or an estimate of the errors committed when using the classical approximation. The method is applied to the case of a few degrees of freedom and compared with other methods and with the exact quantum results. An analysis of the dependence of the numerical effort involved as a function of the number of variables is given, which allows us to be optimistic about its applicability in a quantum field theoretical context.

We investigate the gas density, temperature, and pressure profiles in a dark matter halo under the influence of the chameleon force. We solve the hydrostatic equilibrium equation for the gas coupled with the chameleon field in an analytic manner, using an approximate solution for the chameleon field equation with the source term, with a generalized Navarro-Frenk-White universal density profile. We find that the gas distribution becomes compact because a larger pressure gradient is necessary due to the additional chameleon force. By confronting the theoretical prediction with the data of the temperature profile of the Hydra A cluster according to Suzaku x-ray observations out to the virial radius, we demonstrate that a useful constraint on a model parameter can be obtained depending on the value of the coupling constant. For example, the upper bound of the background value of chameleon field, ${\varphi }_{\infty }<{10}^{-4}{M}_{\mathrm{Pl}}$, is obtained in the case $\beta =1$, where $\beta$ is the coupling constant between the chameleon field and the matter, and $M_{\mathrm{Pl}}$ is the Planck mass. However, the error of the present data is not so small that we obtain a useful constraint in the case $\beta =1/\sqrt{6}$, which corresponds to an $f(R)$ model.

Observations by the Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE-2) and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5–6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5–50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is $\sigma v\approx (0.4–30)\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$, similar to the value predicted for a simple thermal relic ($\sigma v\approx 3\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma-ray background observed by Fermi must result from dark matter as well.

Spherical collapse has turned out to be a successful semianalytic model to study structure formation in different dark energy models and theories of gravity. Nevertheless, the process of virialization is commonly studied on the basis of the virial theorem of classical mechanics. In the present paper, a fully general-relativistic virial theorem based on the Tolman-Oppenheimer-Volkoff solution for homogeneous, perfect-fluid spheres is constructed for the Einstein–de Sitter and $\Lambda \mathrm{CDM}$ cosmologies. We investigate the accuracy of classical virialization studies on cosmological scales and consider virialization from a more fundamental point of view. Throughout, we remain within general relativity and the class of Friedmann-Lemaître-Robertson-Walker models. The virialization equation is set up and solved numerically for the virial radius, $y_{\mathrm{vir}}$, from which the virial overdensity ${\Delta }_V$ is directly obtained. Leading order corrections in the post-Newtonian framework are derived and quantified. In addition, problems in the application of this formalism to dynamical dark energy models are pointed out and discussed explicitly. We show that, in the weak field limit, the relative contribution of the leading-order terms of the post-Newtonian expansion are of the order of ${10}^{-3}\%$ and the solution of Wang and Steinhardt [Astrophys. J. 508, 483 (1998)] is precisely reproduced. Apart from the small corrections, the method could provide insight into the process of virialization from a more fundamental point of view.

We describe a simple way of obtaining horizon entropy using the approach based on the Virasoro algebra and central charge. We show that the Virasoro algebra defined by the Noether currents corresponding to the surface term of gravitational action, for the diffeomorphisms which leave the horizon structure unaltered, has a central extension that directly leads to the horizon entropy. In this approach there are no ambiguities in the calculation of the central charge. We explain why this approach is physically well motivated and could provide greater insight into the nature of horizon entropy.

Instead of the fermion-fermion scattering which identifies the BCS-BEC crossover in cold atom systems, boson-boson scattering is measurable and characterizes the BCS-BEC crossover at quark-level. We study $\pi \mathrm{\text{−}}\pi$ scattering in a pion superfluid described by the Nambu-Jona-Lasinio model. We find that the scattering amplitude drops down monotonically with decreasing isospin density and finally vanishes at the boundary of the phase transition. This indicates a BCS-BEC crossover in the pion superfluid.