The phase structure of QCD with imaginary chemical potential provides information on the phase diagram of QCD with real chemical potential. With imaginary chemical potential $i{\mu }_I=i\pi T$, previous studies show that the Roberge-Weiss (RW) transition endpoints are triple points at both large and small quark masses, and second order transition points at intermediate quark masses. The triple and second order endpoints are separated by two tricritical ones. We present simulations with $N_f=2$ Wilson fermions to investigate the nature of RW transition endpoints. The simulations are carried out at 8 values of the hopping parameter $\kappa$ ranging from 0.020 to 0.140 on different lattice volumes. The Binder cumulant, susceptibility, and reweighted distribution of the imaginary part of the Polyakov loop are employed to determine the nature of RW transition endpoints. The simulations show that the two tricritical points are within the ranges 0.070–0.080 and 0.120–0.140, respectively.

The inclusive production of the gauge bosons $W^{\pm }$ and $Z^0$ is studied within the color dipole formalism. Gluon saturation effects associated with nonlinear corrections to the QCD dynamics, which are expected to contribute at high energies, are naturally included in such formalism. We estimate the contribution of these effects at LHC energies and compare our results with the next-to-next-to-leading order collinear predictions. A comparison with current experimental data is performed and predictions for higher energies are presented.

We study the next-to-next-to-leading logarithmic order resummation for the large $p_T$ Higgs boson production at the LHC in the framework of soft-collinear effective theory. We find that the resummation effects reduce the scale uncertainty significantly and decrease the QCD NLO results by about 11% in the large $p_T$ region. The finite top quark mass effects and the effects of the NNLO singular terms are also discussed.

We calculate differential cross sections for the Higgs boson and/or two-photon production from the intermediate (virtual) Higgs boson within the formalism of $k_t$ factorization. The off-shell $g^{*}{g}^{*}\to H$ matrix elements are used. We compare results obtained with infinite top fermion (quark) mass and with finite mass taken into account. The latter effect is rather small. We compare the results with different unintegrated gluon distributions from the literature. Two methods are used. In the first method first Higgs boson is produced in the $2\to 1$ $gg\to H$ $k_t$-factorization approach and then isotropic decay with the Standard Model branching fraction is performed. In the second method we calculate directly two photons coupled to the virtual Higgs boson. The results of the two methods are compared and differences are discussed. The results for the two photons from the Higgs boson are compared with recent ATLAS Collaboration data. The leading-order $gg\to H$ contribution is rather small compared to the ATLAS experimental data ($\gamma \gamma$ transverse momentum and rapidity distributions) for all unintegrated gluon distributions from the literature. We include also the higher-order contribution $gg\to H(\to \gamma \gamma )g$, $gg\to gHg$ and the contribution of the $W^{+}{W}^{-}$ and $Z^0{Z}^0$. The $gg\to Hg$ mechanism gives a similar cross section as the $gg\to H$ mechanism. We argue that there is almost no double counting when adding $gg\to H$ and $gg\to Hg$ contributions due to the different topology of Feynman diagrams. The final sum is comparable with the ATLAS two-photon data. We discuss uncertainties related to both the theoretical approach and existing unintegrated gluon distribution functions.

We show the results of a coupled-channel quark model calculation of the bottomonium spectrum with self-energy corrections due to the coupling to the meson-meson continuum. We also provide results for the open-bottom strong decay amplitudes of higher bottomonia in a ${{}^{3}P}_0$ model.

The low-energy limit of pure Yang-Mills $SU(3)$ gauge theory is studied in Feynman gauge by the method of stationary variance, a genuine second-order variational method that is suited to deal with the minimal coupling of fermions in gauge theories. In terms of standard irreducible graphs, the stationary equations are written as a set of coupled nonlinear integral equations for the gluon and ghost propagators. A physically sensible solution is found for any strength of the coupling. The gluon propagator is finite in the infrared, with a dynamical mass that decreases as a power at high energies. At variance with some recent findings in Feynman gauge, the ghost dressing function does not vanish in the infrared limit and a decoupling scenario emerges as recently reported for the Landau gauge.

The top-quark mass $M_{\text{top}}$ is measured using top quark-antiquark pairs produced in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV and that decay into a fully hadronic final state. The full data set collected with the CDF II detector at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of $9.3{\mathrm{fb}}^{-1}$, is used. Events are selected that have six to eight jets, at least one of which is identified as having originated from a $b$ quark. In addition, a multivariate algorithm, containing multiple kinematic variables as inputs, is used to discriminate signal events from background events due to QCD multijet production. Templates for the reconstructed top-quark mass are combined in a likelihood fit to measure $M_{\text{top}}$ with a simultaneous calibration of the jet energy scale. A value of $M_{\text{top}}=175.07\pm 1.19(\mathrm{stat}){}_{-1.58}^{+1.55}(\mathrm{syst})\mathrm{GeV}/c^2$ is obtained for the top-quark mass.

There have been some speculations about the existence of critical unitary $O(N)$-invariant scalar field theories in dimensions $4<d<6$ and for large $N$. Using the functional renormalization group equation, we show that in the lowest order of the derivative expansion and assuming that the anomalous dimension vanishes for large $N$, the corresponding critical potentials are either unbounded from below or singular for some finite value of the field.

We study a metastable supersymmetry-breaking vacuum in a generalized O’Raifeartaigh model at finite temperature and chemical potentials. Fields in the generalized O’Raifeartaigh model possess different $R$-charges to realize $R$-symmetry breaking. Accordingly, at finite density and temperature, the chemical potentials have to be introduced in a nonuniform way. Based on the formulation elaborated in our previous work, we study the one-loop thermal effective potential including chemical potentials in the generalized O’Raifeartaigh model. We perform a numerical analysis and find that the $R$-symmetry-breaking vacua, which exist at zero temperature and zero chemical potential, are destabilized for some parameter regions. In addition, we find that there are parameter regions where new $R$-symmetry-breaking vacua are realized even at high temperature by the finite density effects.

We provide a precise statement of hard-soft-collinear factorization of scattering amplitudes and prove it to all orders in perturbation theory. Factorization is formulated as the equality at leading power of scattering amplitudes in QCD with other amplitudes in QCD computed from a product of operator matrix elements. The equivalence is regulator independent and gauge independent. As the formulation relates amplitudes to the same amplitudes with additional soft or collinear particles, it includes as special cases the factorization of soft currents and collinear splitting functions from generic matrix elements, both of which are shown to be process independent to all orders. We show that the overlapping soft-collinear region is naturally accounted for by vacuum matrix elements of kinked Wilson lines. Although the proof is self-contained, it combines techniques developed for the study of pinch surfaces, scattering amplitudes, and effective field theory.

In this paper we report the results of a thorough numerical study of the motion of spinning particles in Kerr spacetime with different prescriptions. We first evaluate the Mathisson-Papapetrou equations with two different spin supplementary conditions, namely, the Tulczyjew and the Newton-Wigner, and make a comparison of these two cases. We then use the Hamiltonian formalism given by Barausse, Racine, and Buonanno [Phys. Rev. D 80, 104025 (2009)] to evolve the orbits and compare them with the corresponding orbits provided by the Mathisson-Papapetrou equations. We include a full description of how to treat the issues arising in the numerical implementation.

We examine the correspondence between QFT observables and bulk solutions in the context of AdS/CFT in the limit as the cosmological constant $\mathrm{\Lambda }\to 0$. We focus specifically on the spacetime metric and a nonbackreacting scalar in the bulk, compute the one-point functions of the dual operators, and determine the necessary conditions for the correspondence to admit a well-behaved zero-$\mathrm{\Lambda }$ limit. We discuss holographic renormalization in this limit and find that it requires schemes that partially break diffeomorphism invariance of the bulk theory. In the specific case of three bulk dimensions, we compute the zero-$\mathrm{\Lambda }$ limit of the holographic Weyl anomaly and reproduce the central charge that arises in the central extension of ${\mathfrak{bms}}_3$. We compute holographically the energy and momentum of those QFT states dual to flat cosmological solutions and to the Kerr solution and find an agreement with the bulk theory. We also compute holographically the renormalized two-point function of a scalar operator in the zero-$\mathrm{\Lambda }$ limit and find it to be consistent with that of a conformal operator in two dimensions fewer. Finally, our results can be used in a new definition of asymptotic Ricci flatness at null infinity based on the zero-$\mathrm{\Lambda }$ limit of asymptotically Einstein manifolds.

The nonperturbative instabilities of hot Kaluza-Klein (KK) spacetime are investigated. In addition to the known instability of hot space (the nucleation of 4D black holes) and the known instability of KK space (the nucleation of bubbles of nothing by quantum tunneling), we find two new instabilities: the nucleation of 5D black holes, and the nucleation of bubbles of nothing by thermal fluctuation. These four instabilities are controlled by two Euclidean instantons, with each instanton doing double duty via two inequivalent analytic continuations; thermodynamic instabilities of one are shown to be related to mechanical instabilities of the other. I also construct bubbles of nothing that are formed by a hybrid process involving both thermal fluctuation and quantum tunneling. There is an exact high-temperature/low-temperature duality that relates the nucleation of black holes to the nucleation of bubbles of nothing.

Dynamical instabilities in protoneutron stars may produce gravitational waves whose observation could shed light on the physics of core-collapse supernovae. When born with sufficient differential rotation, these stars are susceptible to a shear instability (the “low-$T/|W|$ instability”), but such rotation can also amplify magnetic fields to strengths where they have a considerable impact on the dynamics of the stellar matter. Using a new magnetohydrodynamics module for the Spectral Einstein Code, we have simulated a differentially-rotating neutron star in full 3D to study the effects of magnetic fields on this instability. Though strong toroidal fields were predicted to suppress the low-$T/|W|$ instability, we find that they do so only in a small range of field strengths. Below $4\times 10^{13}\mathrm{G}$, poloidal seed fields do not wind up fast enough to have an effect before the instability saturates, while above $5\times 10^{14}\mathrm{G}$, magnetic instabilities can actually amplify a global quadrupole mode (this threshold may be even lower in reality, as small-scale magnetic instabilities remain difficult to resolve numerically). Thus, the prospects for observing gravitational waves from such systems are not in fact diminished over most of the magnetic parameter space. Additionally, we report that the detailed development of the low-$T/|W|$ instability, including its growth rate, depends strongly on the particular numerical methods used. The high-order methods we employ suggest that growth might be considerably slower than found in some previous simulations.

Direct observation of black holes is one of the grand challenges in astronomy. If there are supercompact objects which possess unstable circular orbits of photons, however, it may be difficult to distinguish them from black holes by observing photons. As a model of supercompact objects, we consider a gravastar (gravitational-vacuum-star) which was originally proposed by Mazur and Mottola. For definiteness, we adopt a spherical thin-shell model of a gravastar developed by Visser and Wiltshire, which connects interior de Sitter geometry and exterior Schwarzschild geometry. We find that unstable circular orbits of photons can appear around the gravastar. Then, we investigate the optical images of the gravastar possessing unstable circular orbits, assuming its optically transparent surface and two types of optical sources behind the gravastar: (i) an infinite optical plane and (ii) a companion star. The main feature of the image of (i) is that a bright disk and a dark thick ring surrounding the disk appear in the center of the region which would be completely dark if the compact object was not the gravastar but the Schwarzschild black hole. Also in case (ii), a small disk and arcs around the disk appear in the region which would be completely dark for the lensing image by the Schwarzschild black hole. Because characteristic images appear inside the gravastar in both cases, we could tell the difference between a black hole and a gravastar with high-resolution very-long-baseline-interferometry observations in the near future.

The fraction of primordial black holes (PBHs) of masses ${10}^{17}–{10}^{26}\mathrm{g}$ in the total amount of dark matter may be constrained by considering their capture by neutron stars (NSs), which leads to the rapid destruction of the latter. The constraints depend crucially on the capture rate which, in turn, is determined by the energy loss by a PBH passing through a NS. Two alternative approaches to estimate the energy loss have been used in the literature: the one based on the dynamical friction mechanism, and another on tidal deformations of the NS by the PBH. The second mechanism was claimed to be more efficient by several orders of magnitude due to the excitation of particular oscillation modes reminiscent of the surface waves. We address this disagreement by considering a simple analytically solvable model that consists of a flat incompressible fluid in an external gravitational field. In this model, we calculate the energy loss by a PBH traversing the fluid surface. We find that the excitation of modes with the propagation velocity smaller than that of PBH is suppressed, which implies that in a realistic situation of a supersonic PBH the large contributions from the surface waves are absent and the above two approaches lead to consistent expressions for the energy loss.

We study the clustering of voids using $N$-body simulations and simple theoretical models. The excursion-set formalism describes fairly well the abundance of voids identified with the watershed algorithm, although the void formation threshold required is quite different from the spherical collapse value. The void cross bias $b_{\mathrm{c}}$ is measured and its large-scale value is found to be consistent with the peak background split results. A simple fitting formula for $b_{\mathrm{c}}$ is found. We model the void auto-power spectrum taking into account the void biasing and exclusion effect. A good fit to the simulation data is obtained for voids with radii $\gtrsim 30\mathrm{Mpc}{h}^{-1}$, especially when the void biasing model is extended to 1-loop order. However, the best-fit bias parameters do not agree well with the peak-background results. Being able to fit the void auto-power spectrum is particularly important not only because it is the direct observable in galaxy surveys, but also our method enables us to treat the bias parameters as nuisance parameters, which are sensitive to the techniques used to identify voids.

We report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitational-wave observatories and the partially completed IceCube high-energy neutrino detector, including periods of joint operation between 2007–2010. These include parts of the 2005–2007 run and the 2009–2010 run for LIGO-Virgo, and IceCube’s observation periods with 22, 59 and 79 strings. We find no significant coincident events, and use the search results to derive upper limits on the rate of joint sources for a range of source emission parameters. For the optimistic assumption of gravitational-wave emission energy of ${10}^{-2}{\mathrm{M}}_{\odot }{\mathrm{c}}^2$ at $\sim 150\mathrm{Hz}$ with $\sim 60\mathrm{ms}$ duration, and high-energy neutrino emission of $10^{51}\mathrm{erg}$ comparable to the isotropic gamma-ray energy of gamma-ray bursts, we limit the source rate below $1.6\times 10^{-2}{\mathrm{Mpc}}^{-3}{\mathrm{yr}}^{-1}$. We also examine how combining information from gravitational waves and neutrinos will aid discovery in the advanced gravitational-wave detector era.