Canonical methods can be used to construct effective actions from deformed covariance algebras, as implied by quantum-geometry corrections of loop quantum gravity. To this end, classical constructions are extended systematically to effective constraints of canonical quantum gravity and applied to model systems as well as general metrics, with the following conclusions: (i) Dispersion relations of matter and gravitational waves are deformed in related ways, ensuring a consistent realization of causality. (ii) Inverse-triad corrections modify the classical action in a way clearly distinguishable from curvature effects. In particular, these corrections can be significantly larger than often expected for standard quantum-gravity phenomena. (iii) Finally, holonomy corrections in high-curvature regimes do not signal the evolution from collapse to expansion in a “bounce,” but rather the emergence of the Universe from Euclidean space at high density. This new version of signature-change cosmology suggests a natural way of posing initial conditions, and a solution to the entropy problem.

We discuss a general method to study linear perturbations of slowly rotating black holes which is valid for any perturbation field, and particularly advantageous when the field equations are not separable. As an illustration of the method we investigate massive vector (Proca) perturbations in the Kerr metric, which do not appear to be separable in the standard Teukolsky formalism. Working in a perturbative scheme, we discuss two important effects induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes and bound states with different azimuthal number $m$, and the coupling between axial and polar modes with different multipolar index $\ell$. We explicitly compute the perturbation equations up to second order in rotation, but in principle the method can be extended to any order. Working at first order in rotation we show that polar and axial Proca modes can be computed by solving two decoupled sets of equations, and we derive a single master equation describing axial perturbations of spin $s=0$ and $s=\pm 1$. By extending the calculation to second order we can study the superradiant regime of Proca perturbations in a self-consistent way. For the first time we show that Proca fields around Kerr black holes exhibit a superradiant instability, which is significantly stronger than for massive scalar fields. Because of this instability, astrophysical observations of spinning black holes provide the tightest upper limit on the mass of the photon: $m_{\gamma }\lesssim 4\times {10}^{-20}\mathrm{eV}$ under our most conservative assumptions. Spin measurements for the largest black holes could reduce this bound to $m_{\gamma }\lesssim {10}^{-22}\mathrm{eV}$ or lower.

We study charged black hole solutions in Einstein-Gauss-Bonnet theory with the dilaton field which is the low-energy effective theory of the heterotic string. The spacetime is $D$-dimensional and assumed to be static and spherically symmetric with the ($D-2$)-dimensional constant curvature space and asymptotically flat. The system of the basic equations is complex and the solutions are obtained numerically. We identify the allowed parameter region where the black hole solutions exist, and show configurations of the field functions in $D=4–6$ and 10. We also show the relations of the physical quantities of the black holes such as the horizon radius, the mass, the temperature, and so on, and find several results. The forms of the allowed parameter regions are different depending on the dimension. There is no extreme black hole solution with $T=0$ that can be obtained by taking the limit of the nonextreme solutions within the parameter range we chose. Entropy of the black holes in the dilatonic theory is always larger than that in the nondilatonic theory. Our analysis includes the higher order term of the dilaton field which is not in our previous works. Its effect remarkably appears in five dimensions and is given in the Appendix. By our analysis it is found that the properties of the black hole solutions strongly depend on the dimension, charge, existence of the dilaton field. Hence both the detailed analyses of the individual systems and the investigations from the systematic point of view are important.

The physical phase of causal dynamical triangulations (CDT) is known to be described by an effective, one-dimensional action in which three-volumes of the underlying foliation of the full CDT play a role of the sole degrees of freedom. Here we map this effective description onto a statistical-physics model of particles distributed on a 1d lattice, with site occupation numbers corresponding to the three-volumes. We identify the emergence of the quantum de-Sitter universe observed in CDT with the condensation transition known from similar statistical models. Our model correctly reproduces the shape of the quantum universe and allows us to analytically determine quantum corrections to the size of the universe. In the first-order approximation, these corrections lead to the widening of the CDT universe in the temporal direction. We also investigate the phase structure of the model and show that it reproduces all three phases observed in computer simulations of CDT. In addition, we predict that two other phases may exist, depending on the exact form of the discretized effective action and boundary conditions. We calculate various quantities such as the distribution of three-volumes in our model and discuss how they can be compared with CDT.

We construct a Weyl-invariant extension of topologically massive gravity, which remarkably turns out to include topologically massive electrodynamics, with a Proca mass term, conformally coupled to a scalar field. The action has no dimensionful parameters; therefore, the masses are generated via symmetry breaking either radiatively in flat backgrounds or spontaneously in constant curvature backgrounds. The broken phase of the theory, generically, has a single massive spin-2 and a massive spin-1 excitation. Chiral gravity in asymptotically anti–de Sitter spacetimes does not arise as a low energy theory, while chiral gravity in de Sitter spacetime is not ruled out.

We study the possibility that particle production during inflation could source observable gravity waves on scales relevant for cosmic microwave background experiments. A crucial constraint on such scenarios arises because particle production can also source inflaton perturbations and might ruin the usual predictions for a nearly scale-invariant spectrum of nearly Gaussian curvature fluctuations. To minimize this effect, we consider two models of particle production in a sector that is only gravitationally coupled to the inflaton. For a single instantaneous burst of massive particle production, we find that localized features in the scalar spectrum and bispectrum might be observable, but gravitational wave signatures are unlikely to be detectable (due to the suppressed quadrupole moment of nonrelativistic quanta) without invoking some additional effects. We also consider a model with a rolling pseudoscalar that leads to a continuous production of relativistic gauge field fluctuations during inflation. Here we find that gravitational waves from particle production can actually exceed the usual inflationary vacuum fluctuations in a regime where non-Gaussianity is consistent with observational limits. In this model observable $B$-mode polarization can be obtained for any choice of inflaton potential, and the amplitude of the signal is not necessarily correlated with the scale of inflation.

We consider the case of a coupling in the dark cosmological sector, where a dark energy scalar field modifies the gravitational attraction between dark matter particles. We find that the strength of the coupling $\beta$ is constrained using current Cosmic Microwave Background data, including WMAP7 and the South Pole Telescope (SPT), to be less than 0.063 (0.11) at a 68% (95%) confidence level. Further, we consider the additional effects of the Cosmic Microwave Background lensing amplitude, curvature, effective number of relativistic species, and massive neutrinos and show that the bound from current data on $\beta$ is already strong enough to be rather stable with respect to any of these variables. The strongest effect is obtained when we allow for massive neutrinos, in which case the bound becomes slightly weaker, $\beta <0.084$ (0.14). A larger value of the effective number of relativistic degrees of freedom favors larger couplings between dark matter and dark energy, as well as values of the spectral index closer to 1. Adding the present constraints on the Hubble constant, as well as those from baryon acoustic oscillations and Type Ia supernovae, we find $\beta <0.050$ (0.074). In this case, we also find an interesting likelihood peak for $\beta =0.041$ (still compatible with 0 at $1\sigma$). This peak comes mostly from a slight difference between the Hubble parameter measured by the Hubble Space Telescope and the $\mathrm{WMAP}7+\mathrm{SPT}$ best fit. Finally, we show that forecasts of $\mathrm{\text{Planck}}+\mathrm{SPT}$ mock data can pin down the coupling to a precision of better than 1% and detect whether the marginal peak we find at small nonzero coupling is a real effect.

We show that the gamma ray spectrum observed with the HESS array of Cherenkov telescopes coming from the Galactic Center region and identified with the source HESS J1745-290 is well fitted by the secondary photons coming from dark matter (DM) annihilation over a diffuse power law background. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer $\sim {10}^3$ enhancements in the signal over DM alone simulations. The fitted background from HESS data is consistent with recent Fermi-LAT observations of the same region.

We study the effects of systematic errors in Type Ia supernova (SN Ia) measurements on dark energy (DE) constraints using current data from the Supernova Legacy Survey. We consider how SN systematic errors affect constraints from combined SN Ia, baryon acoustic oscillations, and cosmic microwave background data, given that SNe Ia still provide the strongest constraints on DE but are arguably subject to more significant systematics than the latter two probes. We focus our attention on the temporal evolution of DE described in terms of principal components (PCs) of the equation of state, though we examine a few of the more common, simpler parametrizations as well. We find that the SN Ia systematics degrade the total generalized figure of merit, which characterizes constraints in multidimensional DE parameter space, by a factor of 3 to 4. Nevertheless, overall constraints obtained on roughly five PCs are very good even with current data and systematics. We further show that current constraints are robust to allowing for the finite detection significance of the baryon acoustic oscillations feature in galaxy surveys.

The spin angular momentum $\mathit{S}$ of a supermassive black hole (SBH) precesses due to torques from orbiting stars, and the stellar orbits precess due to dragging of inertial frames by the spinning hole. We solve the coupled post-Newtonian equations describing the joint evolution of $\mathit{S}$ and the stellar angular momenta ${\mathit{L}}_j$, $j=1\dots N$ in spherical, rotating nuclear star clusters. In the absence of gravitational interactions between the stars, two evolutionary modes are found: (1) nearly uniform precession of $\mathit{S}$ about the total angular momentum vector of the system and (2) damped precession, leading, in less than one precessional period, to alignment of $\mathit{S}$ with the angular momentum of the rotating cluster. Beyond a certain distance from the SBH, the time scale for angular momentum changes due to gravitational encounters between the stars is shorter than spin-orbit precession times. We present a model, based on the Ornstein-Uhlenbeck equation, for the stochastic evolution of star clusters due to gravitational encounters and use it to evaluate the evolution of $\mathit{S}$ in nuclei where changes in the ${\mathit{L}}_j$ are due to frame dragging close to the SBH and to encounters farther out. Long-term evolution in this case is well described as uniform precession of the SBH about the cluster’s rotational axis, with an increasingly important stochastic contribution when SBH masses are small. Spin precessional periods are predicted to be strongly dependent on nuclear properties, but typical values are $\sim {10}^7–{10}^8\mathrm{yr}$ for low-mass SBHs in dense nuclei, $\sim {10}^8–{10}^{10}\mathrm{yr}$ for SBH masses $\sim {10}^8{\mathcal{M}}_{\odot }$, and $\sim {10}^{10}–{10}^{11}\mathrm{yr}$ for the most massive SBHs. We compare the evolution of SBH spins in stellar nuclei to the case of torquing by an inclined, gaseous accretion disk.

We comment positively on the recent article “Seesaw mechanism with Occam’s razor” [K. Harigaya et al. Phys. Rev. D 86, 013002 (2012).] by Harigaya, Ibe, and Yanagida. In this article, the authors are using the principle of Occam’s razor in neutrino physics—a principle that should be applied more often in science in general. At the end, we also discuss the Bayesian method in statistics, in which Occam’s razor is naturally built in.

The formation of transitory domain walls is quite generic in theories with spontaneous breaking of discrete symmetries. Since these walls are in conflict with cosmology, there has to be some mechanism which makes them disappear. We study one such mechanism by incorporating Planck-scale suppressed operators within the framework of left-right symmetric models where left-right parity (D parity) is spontaneously broken. We find that this mechanism cannot make the walls disappear in minimal versions of left-right symmetric models. We propose two viable extensions of this model and show that Planck-scale suppressed operators can give rise to the successful disappearance of domain walls provided the scale of parity breaking obeys certain limits. We also constrain the scale of parity breaking by demanding successful gauge-coupling unification and make a comparison of the unification and cosmology bounds.

We study the structure of the energy-momentum tensor of radial excitations of $Q$-balls in scalar field theories with U(1) symmetry. The obtained numerical results for the $1\le N\le 23$ excitations allow us to study in detail patterns how the solutions behave with $N$. We show that although the fields $\varphi (r)$ and energy-momentum tensor densities exhibit a remarkable degree of complexity, the properties of the solutions scale with $N$ with great regularity. This is to the best of our knowledge the first study of the $D$-term $d_1$ for excited states, and we demonstrate that it is negative—in agreement with results from literature on the $d_1$ of ground state particles.

We propose a new framework for investigating two-flavor lattice QCD with finite temperature and density. We consider the Karsten-Wilczek fermion formulation, in which a species-dependent imaginary chemical potential term can reduce the number of species to two without losing chiral symmetry. This lattice discretization is useful for study on finite-$(T,\mu )$ QCD since its discrete symmetries are appropriate for the case. To show its applicability, we study strong-coupling lattice QCD with temperature and chemical potential. We derive the effective potential of the scalar meson field and obtain a critical line of the chiral phase transition, which is qualitatively consistent with the phenomenologically expected phase diagram. We also discuss that $O(1/a)$ renormalization of imaginary chemical potential can be controlled by adjusting a parameter of a dimension-3 counterterm.

We present the results of a calculation of the positive-parity ground-state charmed-baryon spectrum using $2+1+1$ flavors of dynamical quarks. The calculation uses a relativistic heavy-quark action for the valence charm quark, clover-Wilson fermions for the valence light and strange quarks, and highly improved staggered sea quarks. The spectrum is calculated with a lightest pion mass around 220 MeV, and three lattice spacings ($a\approx 0.12$, 0.09, and 0.06 fm) are used to extrapolate to the continuum. The light-quark mass extrapolation is performed using heavy-hadron chiral perturbation theory up to $\mathcal{O}(m_{\pi }^3)$ and at next-to-leading order in the heavy-quark mass. For the well-measured charmed baryons, our results show consistency with the experimental values. For the controversial $J=1/2{\Xi }_{cc}$, we obtain the isospin-averaged value $m_{{\Xi }_{cc}}=3595(39)(20)(6)\mathrm{MeV}$ (the three uncertainties are statistics, fitting-window systematic, and systematics from other lattice artifacts, such as lattice scale setting and pion-mass determination), which shows a $1.7\sigma$ deviation from the experimental value. We predict the yet-to-be-discovered doubly and triply charmed baryons ${\Xi }_{cc}^{*}$, ${\Omega }_{cc}$, ${\Omega }_{cc}^{*}$ and ${\Omega }_{ccc}$ to have masses 3648(42)(18)(7), 3679(40)(17)(5), 3765(43)(17)(5), and 4761(52)(21)(6) MeV, respectively.

We present results on both the restoration of the spontaneously broken chiral symmetry and the effective restoration of the anomalously broken $U(1{)}_A$ symmetry in finite temperature QCD at zero chemical potential using lattice QCD. We employ domain wall fermions on lattices with fixed temporal extent $N_{\tau }=8$ and spatial extent $N_{\sigma }=16$ in a temperature range of $T=139–195\mathrm{MeV}$, corresponding to lattice spacings of $a\approx 0.12–0.18\mathrm{fm}$. In these calculations, we include two degenerate light quarks and a strange quark at fixed pion mass $m_{\pi }=200\mathrm{MeV}$. The strange quark mass is set near its physical value. We also present results from a second set of finite temperature gauge configurations at the same volume and temporal extent with slightly heavier pion mass. To study chiral symmetry restoration, we calculate the chiral condensate, the disconnected chiral susceptibility, and susceptibilities in several meson channels of different quantum numbers. To study $U(1{)}_A$ restoration, we calculate spatial correlators in the scalar and pseudoscalar channels, as well as the corresponding susceptibilities. Furthermore, we also show results for the eigenvalue spectrum of the Dirac operator as a function of temperature, which can be connected to both $U(1{)}_A$ and chiral symmetry restoration via Banks-Casher relations.

We investigate semi-inclusive photon-hadron production in the color-glass-condensate framework at RHIC and the LHC energies in proton-proton ($pp$) and proton-nucleus ($pA$) collisions. We calculate the coincidence probability for azimuthal correlation of pairs of photon-hadron production and show that the away-side correlations have a double-peak or a single-peak structure depending on trigger particle selection and kinematics. This novel feature is unique for semi-inclusive photon-hadron production compared to a similar measurement for double inclusive dihadron production in $pA$ collisions. We obtain necessary conditions between kinematic variables for the appearance of a double-peak or a single-peak structure for the away-side photon-hadron correlations in $pp$ and $pA$ collisions at forward rapidities and show that this feature is mainly controlled by the ratio $z_T=p_T^{\mathrm{hadron}}/p_T^{\mathrm{photon}}$. Decorrelation of away-side photon-hadron production by increasing the energy, rapidity and density, and appearance of double-peak structure can be understood by QCD saturation physics. We also provide predictions for the ratio of single inclusive prompt photon to hadron production, and the two-dimensional nuclear modification factor for the semi-inclusive photon-hadron pair production at RHIC and the LHC at forward rapidities.

Two-body charmless hadronic $B$ decays involving a light tensor meson in their final states are studied in the perturbative QCD approach based on $k_T$ factorization. From our calculations, we find that the decay branching ratios for the color-allowed, tree-dominated decays $B\to a_2^0{\pi }^{+}$ and $B\to a_2^{-}{\pi }^{+}$ are of orders ${10}^{-6}$ and ${10}^{-5}$, respectively, while other color-suppressed, tree-dominated decays have very small branching ratios. In general, the branching ratios of most decays are in the range of ${10}^{-5}$ to ${10}^{-8}$, which are bigger by 1 or 2 orders of magnitude than those predictions obtained in the Isgur-Scora-Grinstein-Wise II model and in the covariant light front approach, but consistent with recent experimental measurements and QCD factorization calculations. Since decays with a tensor meson emitted from vacuum are prohibited in naive factorization, the contributions of nonfactorizable and annihilation diagrams are very important to these decays, which are calculable in our perturbative QCD approach. We also give predictions for the direct $CP$ asymmetries, some of which are large enough for the future experiments to measure. Because we consider the mixing between $f_2$ and $f_2^{\prime }$, the decay rates are enhanced significantly for some decays involving $f_2^{\prime }$ mesons, even with a small mixing angle.

We study a generic Higgs boson and a top quark associated production via model-independent flavor-changing neutral-current couplings at the LHC, including complete QCD next-to-leading order (NLO) corrections to the production and decay of the top quark and the Higgs boson. We find that QCD NLO corrections can increase the total production cross sections by about 48.9% and 57.9% for the $Htu$ and $Htc$ coupling induced processes at the LHC, respectively. After kinematic cuts are imposed on the decay products of the top quark and the Higgs boson, the QCD NLO corrections are reduced to 11% for the $Htu$ coupling induced process and almost vanish for the $Htc$ coupling induced process. Moreover, QCD NLO corrections reduce the dependence of the total cross sections on the renormalization and factorization scales. We also discuss signals of the $tH$ associated production with the decay mode $t\to b{l}^{+}{\mathrm{E̸}}_T$, $H\to b\overline{b}$, and $t\overline{t}$ production with the decay mode $\overline{t}\to H\overline{q}$, $t\to b{l}^{+}{\mathrm{E̸}}_T$. Our results show that, in some parameter regions, the LHC may observe the above signals at the $5\sigma$ level. Otherwise, the upper limits on the flavor-changing neutral-current $Htq$ couplings can be set.

We consider hadronic transitions from the $h_b(2P)$ bottomonium resonance to lower states of bottomonium with emission of either a $\omega$ meson, or two pions, or a $\eta$ meson. For the former two transitions the branching ratios are related to similar transitions from ${\chi }_{b1}(2P)$ and the recently measured Belle fractions of the radiative decays of $h_b(2P)$. We argue that the fraction of the $h_b(2P)$ total decay rate remaining for the annihilation rate is on the verge of contradiction with the parton picture of bottomonium annihilation resulting in similarity between the decays of $h_b(1,2P)$ and ${\chi }_{b1}(1,2P)$. The contradiction gets even stronger, if the transition $h_b(2P)\to {\rm Y}(1S)\eta$ has a branching fraction of a few percent or more. We argue that, although quite uncertain, the latter fraction may indeed be that significant.