We describe an analysis of the First International Pulsar Timing Array Data Challenge, which was designed to test the ability of new and existing algorithms to constrain the properties of a stochastic gravitational-wave background influencing the arrival times of pulsar signals. We employ a robust, unbiased Bayesian framework developed by van Haasteren to study the three Open and Closed data sets of the International Pulsar Timing Array data challenge. We test various models for each data set and use MultiNest to recover the evidence for the purposes of Bayesian model selection. The parameter constraints of the favored model are confirmed using an adaptive Markov chain Monte Carlo technique. Our results for Closed1 favor a gravitational-wave background with strain amplitude at $f=1{\mathrm{yr}}^{-1}$, $A$, of $(1.1\pm 0.1)\times {10}^{-14}$, power spectral index $\gamma =4.30\pm 0.15$ and no evidence for red-timing noise or single sources. The evidence for Closed2 favors a gravitational-wave background with $A=(6.1\pm 0.3)\times {10}^{-14}$, $\gamma =4.34\pm 0.09$, with no red-timing noise or single sources. Finally, the evidence for Closed3 favors the presence of red-timing noise and a gravitational-wave background, with no single sources. The properties of the background are $A=(5\pm 1)\times {10}^{-15}$ and $\gamma =4.23\pm 0.35$, while the properties of the red noise are $N_{\mathrm{red}}=(12\pm 4)\mathrm{ns}$ and ${\gamma }_{\mathrm{red}}=1.5\pm 0.3$. In all cases the redness of the recovered background is consistent with a source population of inspiraling supermassive black-hole binaries. We also investigate the effect that down-sampling of the data sets has on parameter constraints and run time. Finally, we provide a proof-of-principle study of the ability of the Bayesian framework used in this paper to reconstruct the angular correlation of gravitational-wave background induced timing residuals, comparing this to the Hellings and Downs curve.

We explore the question of what happens with the asymptotically highly damped quasinormal modes ($\ell$ fixed, $|{\omega }_I|\to \infty$) when the underlying spacetime has no event horizons. We consider the characteristic oscillations of a scalar field in a large class of asymptotically flat, spherically symmetric, static spacetimes without (absolute) horizons, such that the class accommodates the cases that are known to be of some sort of physical interest. The question of the asymptotic quasinormal modes in such spacetimes is relevant to elucidating the connection between the behavior of the asymptotic quasinormal modes and the quantum properties of event horizons, as put forward in some recent important conjectures. We prove for a large class of asymptotically flat spacetimes without horizons that the scalar field asymptotically highly damped modes do not exist. This provides in our view additional evidence that there is indeed a close link between the asymptotically highly damped modes and the existence of spacetime horizons (and their properties).

Pion propagation in a hadronic fluid with a nonhomogeneous relativistic flow is studied in terms of the linear sigma model. The wave equation turns out to be equivalent to the equation of motion for a massless scalar field propagating in a curved spacetime geometry. The metric tensor depends locally on the soft pion dispersion relation and the four-velocity of the fluid. For a relativistic flow in curved spacetime, the apparent and trapping horizons may be defined in the same way as in general relativity. An expression for the analog surface gravity is derived.

In this paper, we use the joint measurement of geometry and growth rate from matter density perturbations to constrain the holographic dark energy model. The geometry measurement includes type Ia supernovae (SN Ia) Union2.1, full information of cosmic microwave background from WMAP-7 yr, and baryon acoustic oscillation. For the growth rate of matter density perturbations, the results $f(z){\sigma }_8(z)$ measured from the redshift-space distortion in the galaxy power spectrum are employed. Via the Markov chain Monte Carlo method, we try to constrain the model parameter space. The jointed constraint shows that $c={0.750}_{-0.0999-0.173-0.226}^{+0.0976+0.215+0.319}$ and ${\sigma }_8={0.763}_{-0.0465-0.0826-0.108}^{+0.0477+0.0910+0.120}$ with 1, 2, $3\sigma$ regions. After marginalizing the other irrelevant model parameters, we show the evolution of the equation of state of holographic dark energy with respect to the redshift $z$. Though the current cosmic data points favor a phantomlike holographic dark energy universe in the future for the mean values of the model parameters, it can behave like quintessence in $3\sigma$ regions.

We analyze the situation in which the primordial curvature perturbations are produced by the joint effects of an inflaton field and two curvaton fields. We present general equations which allow the reader to obtain $f_{NL}$ for several different scenarios, which differ in the order in which fields decay into radiation after inflation. In order to investigate the physics of these equations, we analyze some simplified situations where the fields are harmonic and both curvatons are frozen at the same expectation value during inflation. We find quite complex behavior—for a given situation where the inflaton contributes a fixed amount to the total curvature perturbation, there are situations where $f_{NL}$ is maximized if both curvatons share equally in contributing the rest, and situations where $f_{NL}$ is maximized if only one of the two curvatons contributes the rest. We are unable, therefore, to make any completely general extrapolations about the expected non-Gaussianity from $N$ curvatons. We find that as the curvaton contribution to the overall perturbation is gradually increased, $f_{NL}$ rises to a maximum before falling again, and that a given $f_{NL}$ can correspond to many different parameter sets for the two curvatons.

We present numerical simulations of stellar core collapse with spherically symmetric, general relativistic hydrodynamics up to black hole formation. Using the CoCoNuT code, with a newly developed grey leakage scheme for the neutrino treatment, we investigate the effects of including pions and $\Lambda$ hyperons into the equation of state at high densities and temperatures on the black hole formation process. Results show non-negligible differences between the models with reference equation of state without any additional particles and models with the extended ones. For the latter, the maximum masses supported by the proto-neutron star are smaller and the collapse to a black hole occurs earlier. A phase transition to hyperonic matter is observed when the progenitor allows for a high enough accretion rate onto the proto-neutron star. Rough estimates of neutrino luminosity from these collapses are given, too.

Many recent works on large $N$ holographic QCD in the planar limit have not considered UV completions, restricting exclusively toward analyzing the IR physics. Because of this, the UV problems like Landau poles and divergences of Wilson loops including instabilities at high temperatures have not been addressed. In some of our recent papers, we have discussed a possible UV completion, which is conformal in the UV and confining in the far IR, that avoids the Landau poles and the Wilson loop divergences. In this paper we give general field theoretic considerations of this including the complete renormalization group flow. We extend our UV complete model to study scenarios both above and below the deconfinement temperature and argue how phase transition in our model should be understood. Interestingly, because of the UV completion, subtle issues like instability owing to negative specific heat do not appear.

Among different measured observables of top-antitop quark pairs at hadron colliders, the forward-backward asymmetry ($A_{\mathrm{FB}}$) measured by the CDF and D0 collaborations has inconsistency with the Standard Model prediction. The measured forward-backward asymmetry grows with $t\overline{t}$ invariant mass. Several new physics models have been proposed to explain this deviation. We consider the consistency of the parameter space of vector unparticle (in the flavor-conserving scenario) with the existing $t\overline{t}$ production measurements. In particular, we look at the total cross sections at the LHC and Tevatron, differential cross section with $t\overline{t}$ invariant mass, and the LHC charge asymmetry to identify the regions in parameter space that can give the desired top $A_{\mathrm{FB}}$ observed by the Tevatron. We show that, in spite of the intrinsic tension between the LHC charge asymmetry and $A_{\mathrm{FB}}$, there exists a small region in the unparticle parameters space where the top $A_{\mathrm{FB}}$ and the LHC charge asymmetry are satisfied simultaneously. Finally, we show that the consistent region with $t\overline{t}$ observables is consistent with the constraints coming from the dijet resonance searches.

The Schwinger-Dyson Bethe-Salpeter approach to the bound state problem is applied to the spin zero glueball spectrum. Although a moderately successful description of the two-point functions and the glueball spectrum can be obtained, further work is required to reduce sensitivity to model truncations.

In a Peccei-Quinn extension of supergravity the $h\to \gamma \gamma$ detection rate can be significantly enhanced due to the reduction of the total Higgs decay width. To assess the viability of various Peccei-Quinn extensions of minimal supergravity we perform a Bayesian analysis on three such scenarios. The main constraints on these models come from the currently observed Higgs-boson like state by the Large Hadron Collider and from the Wilkinson Microwave Anisotropy Probe observation of dark matter abundance. Our comparative study reveals that under these constraints the Peccei-Quinn violating scenarios with axino dark matter are clearly preferred over the minimal supergravity model with the lightest neutralino as a dark matter candidate.

We revisit the issue of considering stochasticity of Grassmannian coordinates in $N=1$ superspace, which was analyzed previously by Kobakhidze et al. In this stochastic supersymmetry (SUSY) framework, the soft SUSY breaking terms of the minimal supersymmetric Standard Model (MSSM) such as the bilinear Higgs mixing, trilinear coupling, as well as the gaugino mass parameters are all proportional to a single mass parameter $\xi$, a measure of supersymmetry breaking arising out of stochasticity. While a nonvanishing trilinear coupling at the high scale is a natural outcome of the framework, a favorable signature for obtaining the lighter Higgs boson mass $m_h$ at 125 GeV, the model produces tachyonic sleptons or staus turning to be too light. The previous analyses took $\Lambda$, the scale at which input parameters are given, to be larger than the gauge coupling unification scale $M_G$ in order to generate acceptable scalar masses radiatively at the electroweak scale. Still, this was inadequate for obtaining $m_h$ at 125 GeV. We find that Higgs at 125 GeV is highly achievable, provided we are ready to accommodate a nonvanishing scalar mass soft SUSY breaking term similar to what is done in minimal anomaly mediated SUSY breaking (AMSB) in contrast to a pure AMSB setup. Thus, the model can easily accommodate Higgs data, LHC limits of squark masses, WMAP data for dark matter relic density, flavor physics constraints, and XENON100 data. In contrast to the previous analyses, we consider $\Lambda =M_G$, thus avoiding any ambiguities of a post-grand unified theory physics. The idea of stochastic superspace can easily be generalized to various scenarios beyond the MSSM.

We present a toy model in which the Higgs sector fields transform as non-Abelian representations of a family symmetry group, and consider the possibility that the extra family partners of the Higgs particles act as messengers for both supersymmetry and family symmetry breakings. Although such mediation schemes generically produce family dependent soft supersymmetry breaking terms at the messenger scale, we demonstrate the existence of a focusing mechanism which may erase such hierarchies through renormalization group running.

We construct energy-independent but nonlocal potentials above inelastic thresholds, in terms of Nambu-Bethe-Salpeter wave functions defined in quantum field theories such as QCD. As an explicit example, we consider $NN\to NN+n\pi$ scattering processes for $n=0,1,2,\dots$. We show the existence of energy-independent coupled channel potentials with a nonrelativistic approximation, where momenta of all particles are small compared with their own masses. In the case of two-body inelastic scatterings such as $\Lambda \Lambda \to \Lambda \Lambda$, $N\Xi$, $\Sigma \Sigma$, on the other hand, we show that energy-independent potentials can be constructed without relying on nonrelativistic approximations. We also propose a method to extract these potentials using time dependence of general correlation functions.

Numerical lattice gauge theory computations to generate gauge field configurations including the effects of dynamical fermions are usually carried out using algorithms that require the molecular dynamics evolution of gauge fields using symplectic integrators. Sophisticated integrators are commonly used but hard to optimize, and force-gradient integrators show promise especially for large lattice volumes. We explain that symplectic integrators lead to very efficient Monte Carlo algorithms because they exactly conserve a shadow Hamiltonian. The shadow Hamiltonian may be expanded in terms of Poisson brackets and can be used to optimize the integrators. We show how this may be done for gauge theories by extending the formulation of Hamiltonian mechanics on Lie groups to include Poisson brackets and shadows and by giving a general method for the practical computation of forces, force gradients, and Poisson brackets for gauge theories.

We explain the physical nature of the subset solution to the sign problem in chiral random matrix theory: the subset sum over configurations is shown to project out the canonical determinant with zero quark charge from a given configuration. As the grand canonical chiral random matrix partition function is independent of the chemical potential, the zero-quark-charge sector provides the full result.

We study the factorization and resummation of $t$-channel top quark transverse momentum distribution at large $p_T$ in the standard model at both the Tevatron and the LHC with soft-collinear effective theory. The cross section in the threshold region can be factorized into a convolution of hard, jet and soft functions. In particular, we first calculate the next-to-leading order soft functions for this process, and give a renormalization group improved cross section by evolving the different functions to a common scale. Our results show that the resummation effects increase the next-to-leading order results by about $9\%\sim 13\%$ and $4\%\sim 9\%$ when the top quark $p_T$ is larger than 50 and 70 GeV at the Tevatron and the 8 TeV LHC, respectively. Also, we discuss the scale independence of the cross section analytically, and show how to choose the proper scales at which the perturbative expansion can converge fast.

A methodology of including QCD next-to-leading-order corrections in the quark-gluon Monte Carlo shower is outlined. The work concentrates on two issues: (i) constructing the leading-order parton-shower Monte Carlo from scratch, such that it rigorously extends collinear factorization into the exclusive (fully unintegrated) one which we call the Monte Carlo factorization scheme; (ii) introducing next-to-leading-order (NLO) corrections to the hard process in this new environment. The presented solution is designed to be extended to the full NLO-level Monte Carlo, including NLO corrections not only in the hard process but in the whole shower. The issue of the difference between the factorization scheme implemented in the Monte Carlo (MC) solution and the standard $\overline{MS}$ scheme is addressed. The principal MC implementation is designed for the electroweak boson production process at the LHC, but in order to discuss universality (process independence), the deep inelastic lepton-hadron scaterring is also brought into the MC framework.

Recent experimental results on exclusive semitauonic $B$ meson decays, $\overline{B}\to D^{(*)}\tau \overline{\nu }$, showing sizable deviations from the standard model prediction, suggest a new physics in which the structure of the relevant weak charged interaction may differ from that of the standard model. We study the exclusive semitauonic $B$ decays in a model-independent manner using the most general set of four-fermion interactions in order to clarify possible structures of the charged current in new physics. It turns out that correlations among observables including tau and $D^{*}$ polarizations and $q^2$ distributions are useful to distinguish possible new physics operators. Further, we investigate some interesting models to exhibit the advantage of our model-independent analysis. As a result, we find that two Higgs doublet models without tree-level flavor changing neutral currents and the minimal supersymmetric standard model with $R$-parity violation are unlikely to explain the present experimental data, while two Higgs doublet models with flavor changing neutral currents and a leptoquark model are consistent with the data.

The nucleon and its negative-parity excited states are examined in a maximum entropy method analysis of QCD sum rules. First, we rederive the parity projected sum rules for baryons using “old-fashioned” correlation functions. Doing this, the method is generalized so that higher order operator product expansion terms can be calculated unambiguously. We then apply this approach to the nucleon channel taking into account all known first order ${\alpha }_s$ corrections to the Wilson coefficients of the operator product expansion. As these corrections have turned out to be large, we suppress them by using a phase-rotated Gaussian kernel. Simultaneously, this phase rotation strongly suppresses the continuum contribution and improves the convergence of the operator product expansion. The resulting sum rule has the interesting feature that it is dominated by the term containing the chiral condensate of dimension 3. Analyzing this sum rule by the maximum entropy method, we are able to extract information of both the positive- and negative-parity states.

We extend our investigation of backgrounds to new physics signals, following CMS’s data-driven search for supersymmetry at the LHC. The aim is to use different sets of cuts in $\gamma +3$-jet production to predict the irreducible $Z+3$-jet background (with the $Z$ boson decaying to neutrinos) to searches with ${\mathrm{E̸}}_T+3$-jet signal topologies. We compute ratios of $Z+3$-jet to $\gamma +3$-jet production cross sections and kinematic distributions at next-to-leading order (NLO) in ${\alpha }_s$. We compare these ratios with those obtained using a parton shower matched to leading-order matrix elements ($\mathrm{ME}+\mathrm{PS}$). This study extends our previous work [Bern et al., Phys. Rev. D 84, 114002 (2011)] on the $Z+2$-jet to $\gamma +2$-jet ratio. We find excellent agreement with the ratio determined from the earlier NLO results involving two instead of three jets, and agreement to within 10% between the NLO and $\mathrm{ME}+\mathrm{PS}$ results for the ratios. We also examine the possibility of large QCD logarithms in these processes. Ratios of $Z+n$-jet to $\gamma +n$-jet cross sections are plausibly less sensitive to such corrections than the cross sections themselves. Their effect on estimates of $Z+3$-jet to $\gamma +3$-jet ratios can be assessed experimentally by measuring the $\gamma +3$-jet to $\gamma +2$-jet production ratio in search regions. We partially address the question of potentially large electroweak logarithms by computing the real-emission part of the electroweak corrections to the ratio using $\mathrm{ME}+\mathrm{PS}$ and find that it is 1% or less. Our estimate of the remaining theoretical uncertainties in the $Z$ to $\gamma$ ratio is in agreement with our earlier study.