We study general properties of the Landau-gauge Gribov ghost form factor $\sigma (p^2)$ for $\mathrm{SU}(N_c)$ Yang-Mills theories in the $d$-dimensional case. We find a qualitatively different behavior for $d=3$, 4 with respect to the $d=2$ case. In particular, considering any (sufficiently regular) gluon propagator $\mathcal{D}(p^2)$ and the one-loop-corrected ghost propagator, we prove in the $2d$ case that the function $\sigma (p^2)$ blows up in the infrared limit $p\to 0$ as $-\mathcal{D}(0)\ln (p^2)$. Thus, for $d=2$, the no-pole condition $\sigma (p^2)<1$ (for $p^2>0$) can be satisfied only if the gluon propagator vanishes at zero momentum, that is, $\mathcal{D}(0)=0$. On the contrary, in $d=3$ and 4, $\sigma (p^2)$ is finite also if $\mathcal{D}(0)>0$. The same results are obtained by evaluating the ghost propagator $\mathcal{G}(p^2)$ explicitly at one loop, using fitting forms for $\mathcal{D}(p^2)$ that describe well the numerical data of the gluon propagator in two, three and four space-time dimensions in the SU(2) case. These evaluations also show that, if one considers the coupling constant $g^2$ as a free parameter, the ghost propagator admits a one-parameter family of behaviors ( labeled by $g^2$), in agreement with previous works by Boucaud et al. In this case the condition $\sigma (0)\le 1$ implies $g^2\le g_c^2$, where $g_c^2$ is a “critical” value. Moreover, a freelike ghost propagator in the infrared limit is obtained for any value of $g^2$ smaller than $g_c^2$, while for $g^2=g_c^2$ one finds an infrared-enhanced ghost propagator. Finally, we analyze the Dyson-Schwinger equation for $\sigma (p^2)$ and show that, for infrared-finite ghost-gluon vertices, one can bound the ghost form factor $\sigma (p^2)$. Using these bounds we find again that only in the $d=2$ case does one need to impose $\mathcal{D}(0)=0$ in order to satisfy the no-pole condition. The $d=2$ result is also supported by an analysis of the Dyson-Schwinger equation using a spectral representation for the ghost propagator. Thus, if the no-pole condition is imposed, solving the $d=2$ Dyson-Schwinger equations cannot lead to a massive behavior for the gluon propagator. These results apply to any Gribov copy inside the so-called first Gribov horizon; i.e., the $2d$ result $\mathcal{D}(0)=0$ is not affected by Gribov noise. These findings are also in agreement with lattice data.

Chern-Simons (CS) forms generalize the minimal coupling between gauge potentials and point charges to sources represented by charged extended objects (branes). The simplest example of such a CS-brane coupling is a domain wall coupled to the electromagnetic CS three-form. This describes a topologically charged interface where the CS form $A\wedge dA$ is supported, separating two three-dimensional spatial regions in $3+1$ spacetime. Electrodynamics at either side of the brane is described by the same Maxwell’s equations, but those two regions have different vacua characterized by a different value of the $\theta$-parameter multiplying the Pontryagin form $F\wedge F$. The $\theta$-term is the Abelian version of the concept introduced by ’t Hooft for the resolution of the $U(1)$ problem in QCD. We point out that CS-generalized classical electrodynamics show new phenomena when two neighboring regions with different $\theta$-vacua are present. These topological effects result from surface effects induced by the boundary, and we explore the consequences of such boundary effects for the propagation of the electromagnetic field in Maxwell theory. Several features including optical and electrostatic/magnetostatic responses, which may be observable in condensed matter systems like topological insulators, are discussed.

All quadratic translation- and gauge-invariant photon operators for Lorentz breakdown are included into the Stueckelberg Lagrangian for massive photons in a generalized $R_{\xi }$ gauge. The corresponding dispersion relation and tree-level propagator are determined exactly, and some leading-order results are derived. The question of how to include such Lorentz-violating effects into a perturbative quantum-field expansion is addressed. Applications of these results within Lorentz-breaking quantum-field theories include the regularization of infrared divergences as well as the free propagation of massive vector bosons.

We consider a quantum field which is in a Hartle-Hawking state propagating in a spherically symmetric black hole space-time. We calculate the components of the stress tensor, renormalized using the Hadamard form of the Green’s function, in the exterior region of this space-time. We then specialize these results to the case of the “lukewarm” Riessner-Nordstrom-de Sitter black hole.

We calculate graviton $n$-point functions in an anti-de Sitter black brane background for effective gravity theories whose linearized equations of motion have at most two time derivatives. We compare the $n$-point functions in Einstein gravity to those in theories whose leading correction is quadratic in the Riemann tensor. The comparison is made for any number of gravitons and for all physical graviton modes in a kinematic region for which the leading correction can significantly modify the Einstein result. We find that the $n$-point functions of Einstein gravity depend on at most a single angle, whereas those of the corrected theories may depend on two angles. For the four-point functions, Einstein gravity exhibits linear dependence on the Mandelstam variable $s$ versus a quadratic dependence on $s$ for the corrected theory.

We show that a quantum scalar particle in the gravitational field of a massive body of radius $R$ which slightly exceeds the Schwarzschild radius $r_s$, possesses a dense spectrum of narrow resonances. Their lifetimes and density tend to infinity in the limit $R\to r_s$. We determine the cross section of the particle capture into these resonances and show that it is equal to the absorption cross section for a Schwarzschild black hole. Thus, a nonsingular static metric acquires black-hole properties before the actual formation of a black hole.

Cosmological measurements are affected by the energy density of massive neutrinos. We extend here a recent analysis of current cosmological data to nonminimal cosmologies. Several possible scenarios are examined: a constant $w\ne -1$ dark energy equation of state, a nonflat universe, a time-varying dark energy component and coupled dark matter-dark energy universes or modified gravity scenarios. When considering cosmological data only, ($3+2$) massive neutrino models with $\sim 0.5\mathrm{eV}$ sterile species are allowed at 95% confidence level. This scenario has been shown to reconcile reactor, LSND and MiniBooNE positive signals with null results from other searches. Big bang nucleosynthesis bounds could compromise the viability of ($3+2$) models if the two sterile species are fully thermalized states at decoupling.

The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse emission measured by the Fermi Large Area Telescope at Galactic latitudes $|b|>30°$ in four energy bins spanning 1–50 GeV. At multipoles $\ell \ge 155$, corresponding to angular scales $\lesssim 2°$, angular power above the photon noise level is detected at $>99.99\%$ confidence level in the 1–2 GeV, 2–5 GeV, and 5–10 GeV energy bins, and at $>99\%$ confidence level at 10–50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles $\ell \ge 155$, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, $C_{\mathrm{P}}/⟨I{⟩}^2=9.05\pm 0.84\times {10}^{-6}\mathrm{sr}$, while the energy dependence of $C_{\mathrm{P}}$ is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index ${\Gamma }_{\mathrm{s}}=2.40\pm 0.07$. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background.

The absolute neutrino mass scale is currently unknown, but can be constrained by cosmology. The WiggleZ high redshift, star-forming, and blue galaxy sample offers a complementary data set to previous surveys for performing these measurements, with potentially different systematics from nonlinear structure formation, redshift-space distortions, and galaxy bias. We obtain a limit of $\sum _{}^{}{m}_{\nu }<0.60\mathrm{eV}$ (95% confidence) for $\mathrm{WiggleZ}+\mathrm{Wilkinson}\mathrm{Microwave}\mathrm{Anisotropy}\mathrm{Probe}$. Combining with priors on the Hubble parameter and the baryon acoustic oscillation scale gives $\sum _{}^{}{m}_{\nu }<0.29\mathrm{eV}$, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.

We suggest trying to count the number of invisible particles produced in missing energy events at the LHC, arguing that multiple production of such particles provides evidence that they constitute stable dark matter and that counting them could yield further insights into the nature of dark matter. We propose a method to count invisible particles, based on fitting the shapes of certain transverse- or invariant-mass distributions, discuss various effects that may affect the measurement, and simulate the use of the method to count neutrinos in standard model processes and dark matter candidates in new physics processes.

The production cross sections of the inclusive Drell-Yan processes $W^{\pm }\to \ell \nu$ and $Z/{\gamma }^{*}\to \ell \ell$ ($\ell =e$, $\mu$) are measured in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector. The cross sections are reported integrated over a fiducial kinematic range, extrapolated to the full range, and also evaluated differentially as a function of the $W$ decay lepton pseudorapidity and the $Z$ boson rapidity, respectively. Based on an integrated luminosity of about $35{\mathrm{pb}}^{-1}$ collected in 2010, the precision of these measurements reaches a few percent. The integrated and the differential $W^{\pm }$ and $Z/{\gamma }^{*}$ cross sections in the $e$ and $\mu$ channels are combined, and compared with perturbative QCD calculations, based on a number of different parton distribution sets available at next-to-next-to-leading order.

We present a measurement of the $CP$-violating parameter ${\beta }_s^{J/\psi \varphi }$ using approximately 6500 $B_s^0\to J/\psi \varphi$ decays reconstructed with the CDF II detector in a sample of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $5.2{\mathrm{fb}}^{-1}$ integrated luminosity produced by the Tevatron collider at Fermilab. We find the $CP$-violating phase to be within the range ${\beta }_s^{J/\psi \varphi }\in [0.02,0.52]\cup [1.08,1.55]$ at 68% confidence level where the coverage property of the quoted interval is guaranteed using a frequentist statistical analysis. This result is in agreement with the standard model expectation at the level of about one Gaussian standard deviation. We consider the inclusion of a potential $S$-wave contribution to the $B_s^0\to J/\psi K^{+}{K}^{-}$ final state which is found to be negligible over the mass interval $1.009<m(K^{+}{K}^{-})<1.028\mathrm{GeV}/c^2$. Assuming the standard model prediction for the $CP$-violating phase ${\beta }_s^{J/\psi \varphi }$, we find the $B_s^0$ decay width difference to be $\Delta {\Gamma }_s=0.075\pm 0.035(\mathrm{stat})\pm 0.006(\mathrm{syst}){\mathrm{ps}}^{-1}$. We also present the most precise measurements of the $B_s^0$ mean lifetime $\tau (B_s^0)=1.529\pm 0.025(\mathrm{stat})\pm 0.012(\mathrm{syst})\mathrm{ps}$, the polarization fractions $|A_0(0){|}^2=0.524\pm 0.013(\mathrm{stat})\pm 0.015(\mathrm{syst})$ and $|A_{\parallel }(0){|}^2=0.231\pm 0.014(\mathrm{stat})\pm 0.015(\mathrm{syst})$, as well as the strong phase ${\delta }_{\perp }=2.95\pm 0.64(\mathrm{stat})\pm 0.07(\mathrm{syst})\mathrm{rad}$. In addition, we report an alternative Bayesian analysis that gives results consistent with the frequentist approach.

The two Higgs doublets model (2HDM) has provided a very useful way to describe a minimal extension of the scalar sector of the standard model. In this work, it is shown a scheme that we call partial aligned two Higgs doublet model which allows a description of the distinct versions of the 2HDM in a simple way, including those with flavor symmetries. In addition, it is shown a method to diagonalize Yukawa matrices of four-zero texture coming from the 2HDM-III. We provide some phenomenological applications in order to show the model’s predictive power.

We present a new approach to Reggeization of gauge amplitudes, based on the universal properties of their infrared singularities. Using the dipole formula, a compact ansatz for infrared singularities of massless amplitudes, we study Reggeization of singular contributions to high-energy amplitudes for arbitrary color representations, and any logarithmic accuracy. We derive leading-logarithmic Reggeization for general cross-channel exchanges, and we show that the simplest form of Regge factorization breaks down for imaginary parts of amplitudes at next-to-leading logarithms and for real parts at next-to-next-to-leading logarithms. Our formalism applies to multiparticle amplitudes in multi-Regge kinematics, and constrains possible corrections to the dipole formula at three loops and beyond.

Subhorizon approximation is often used in cosmological perturbation theory. In this paper, however, it is shown that the subhorizon approximation is not always a good approximation at least in the case of the $k$-essence model. We also show that the sound speed given by the $k$-essence model exerts a huge influence on the time evolution of the matter density perturbation, and future observations could clarify the differences between the $\Lambda \mathrm{CDM}$ model and the $k$-essence model.

We study the implications for two-Higgs-doublet models of the recent announcement at the LHC giving a tantalizing hint for a Higgs boson of mass 125 GeV decaying into two photons. We require that the experimental result be within a factor of 2 of the theoretical standard model prediction, and analyze the type I and type II models as well as the lepton-specific and flipped models, subject to this requirement. It is assumed that there is no new physics other than two Higgs doublets. In all of the models, we display the allowed region of parameter space taking the recent LHC announcement at face value, and we analyze the $W^{+}{W}^{-}$, $ZZ$, $\overline{b}b$, and ${\tau }^{+}{\tau }^{-}$ expectations in these allowed regions. Throughout the entire range of parameter space allowed by the $\gamma \gamma$ constraint, the numbers of events for Higgs decays into $WW$, $ZZ$, and $b\overline{b}$ are not changed from the standard model by more than a factor of 2. In contrast, in the lepton-specific model, decays to ${\tau }^{+}{\tau }^{-}$ are very sensitive across the entire $\gamma \gamma$-allowed region.

Motivated by recent anomalous CDF data on $Wjj$ events, we study a possible explanation within the framework of the two-Higgs doublet model. We find that a charged Higgs boson of mass $\sim 140\mathrm{GeV}$ with appropriate couplings can account for the observed excess. In addition, we consider the flavor-changing neutral current effects induced at loop level by the charged Higgs boson on the $B$ meson system to further constrain the model. Our study shows that the like-sign charge asymmetry $A_{s\ell }^b$ can be of $\mathcal{O}({10}^{-3})$ in this scenario.

We complete a program of study of $\mathrm{SU}(N)$ gauge theories coupled to two flavors of fermions in the two-index symmetric representation by performing numerical simulations in SU(4). The beta function, defined and calculated via the Schrödinger functional, runs more slowly than the two-loop perturbative result. The mass anomalous dimension levels off in strong coupling at a value of about 0.45, rendering this theory unsuitable for walking technicolor. A large-$N$ comparison of these data with results from SU(2) and SU(3) reveals striking regularities.

Inspired by the observed $Y(2175)$ state, we predict its nonstrange partner $Y(1915)$, which has a resonance structure with mass around 1915 MeV and width about 317–354 MeV. Experimental search for $Y(1915)$ is proposed by analyzing the $\omega f_0(980)$ or $\omega \pi \pi$ invariant mass spectrum of the $e^{+}{e}^{-}\to \omega f_0(980)$, $\omega \pi \pi$, and $J/\psi \to \eta \omega f_0(980)$ processes, which are accessible at Belle, BABAR, BESIII and forthcoming BelleII. Considering similarity between two families, the comparison of the mass spectra of $\omega$ and $\varphi$ families can provide important information on the $1D$ state of $\varphi$ family, $\varphi (1910)$, which has a very broad resonance structure with mass around 1910 MeV regarded as the strangeonium partner of $\omega (1650)$. This also answers the question why the $1D$ state $\varphi (1910)$ is still missing in experiment. This is supported by our former study on the properties of $Y(2175)$, which explains $Y(2175)$ as the $2D$ strangeonium because our theoretical total width is comparable with the Belle data.

We show that the type III seesaw mechanism opens up a promising possibility of searching the Higgs boson in the $b\overline{b}$ channel through the Higgs production associated with a charged lepton coming from the decay of the triplet seesaw particle. In particular we look for the $2b$ signals with trileptons or same-sign dileptons to construct the Higgs and the triplet fermion mass and calculate the reach with the integrated luminosity of $10{\mathrm{fb}}^{-1}$ at the 14 TeV LHC.