We study two types of entropic-force models in a homogeneous, isotropic, spatially flat, matter-dominated universe. The first type is a $\mathrm{\Lambda }(t)$ type similar to $\mathrm{\Lambda }(t)\mathrm{CDM}$ (varying-lambda cold dark matter) models in which both the Friedmann equation and the acceleration equation include an extra driving term. The second type is a BV type similar to bulk viscous models in which the acceleration equation includes an extra driving term but the Friedmann equation does not. In order to examine the two types systematically, we consider an extended entropic-force model that includes a Hubble parameter ($H$) term and a constant term in entropic-force terms. The $H$ term is derived from a volume entropy, whereas the constant term is derived from an entropy proportional to the square of an area entropy. Based on the extended entropic-force model, we examine four models obtained from combining the $H$ and constant terms with the $\mathrm{\Lambda }(t)$ and BV types. The four models agree well with the observed supernova data and describe the background evolution of the late universe properly. However, the evolution of first-order density perturbations is different in each of the four models, especially for low redshift, assuming that an effective sound speed is negligible. The $\mathrm{\Lambda }(t)$ type is found to be consistent with the observed growth rate of clustering, in contrast with the BV type examined in this study. A unified formulation is proposed as well, in order to systematically examine density perturbations of the two types.

We obtain the dipolar anisotropies in the arrival directions of ultrahigh energy cosmic rays diffusing from nearby extragalactic sources. We discuss both the energy regime of spatial diffusion and the quasirectilinear one leading to just angular diffusion at higher energies. We obtain analytic results for the anisotropies from a single source, which are validated using two different numerical simulations. For a scenario with a few sources in the local supercluster (with the closest source at a typical distance of few to tens of Mpc), we discuss the possible transition between the case in which the anisotropies are dominated by a few sources at energies below few EeV towards the regime in which many sources contribute at higher energies. The effect of a nonisotropic source distribution is also discussed, showing that it can significantly affect the observed dipole.

The Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo recently completed searches for gravitational waves at their initial target sensitivities, and soon Advanced LIGO and Advanced Virgo will commence observations with even better capabilities. In the search for short-duration signals, such as coalescing compact binary inspirals or “burst” events, noise transients can be problematic. Interferometric gravitational-wave detectors are highly complex instruments, and, based on the experience from the past, the data often contain a large number of noise transients that are not easily distinguishable from possible gravitational-wave signals. In order to perform a sensitive search for short-duration gravitational-wave signals it is important to identify these noise artifacts, and to “veto” them. Here we describe such a veto, the bilinear-coupling veto, that makes use of an empirical model of the coupling of instrumental noise to the output strain channel of the interferometric gravitational-wave detector. In this method, we check whether the data from the output strain channel at the time of an apparent signal is consistent with the data from a bilinear combination of auxiliary channels. We discuss the results of the application of this veto to recent LIGO data, and its possible utility when used with data from Advanced LIGO and Advanced Virgo.

The exact Foldy-Wouthuysen Hamiltonian is derived for a pointlike spin-1 particle with a normal magnetic moment in a nonuniform magnetic field. For a uniform magnetic field, it is exactly separated into terms linear and quadratic in spin. New unexpected properties of a particle with an anomalous magnetic moment are found. Spin projections of a particle moving in a uniform magnetic field are not integer, and the tensor polarization is asymmetric in the plane orthogonal to the field. Previously described spin-tensor effects caused by the tensor magnetic polarizability exist not only for nuclei but also for pointlike particles.

We study the alignment of the vacuum in gauge theories with $N_f$ Dirac fermions transforming according to a complex representation of the gauge group. The alignment of the vacuum is produced by adding a small mass perturbation to the theory. We study in detail the $N_f=2,3$, and 4 case. For $N_f=2$ and $N_f=3$ we reproduce earlier known results including the Dashen phase with spontaneous violation of the combined charge conjugation and parity symmetry, $CP$. For $N_f=4$ we find regions with and without spontaneous $CP$ violation. We then generalize to an arbitrary number of flavors. Here it is shown that at the point where $N_f-1$ flavors are degenerate with positive mass $m>0$ and the mass of the $N_f$th flavor becomes negative and equal to $-m$, $CP$ breaks spontaneously.

In this paper we present chiral extrapolation formulas for the generalized form factors connected to the first moments of chiral-even generalized parton distributions. For the description of QCD at low energies we employ the framework of two-flavor covariant baryon chiral perturbation theory at full one-loop accuracy. Our results are well suited for the extrapolation of lattice QCD data to physical quark masses.

We consider the two-Higgs-doublet model as a framework in which to evaluate the viability of scenarios in which the sign of the coupling of the observed Higgs boson to down-type fermions (in particular, $b$-quark pairs) is opposite to that of the Standard Model (SM), while at the same time all other tree-level couplings are close to the SM values. We show that, whereas such a scenario is consistent with current LHC observations, both future running at the LHC and a future $e^{+}{e}^{-}$ linear collider could determine the sign of the Higgs coupling to $b$-quark pairs. Discrimination is possible for two reasons. First, the interference between the $b$-quark and the $t$-quark loop contributions to the $ggh$ coupling changes sign. Second, the charged-Higgs loop contribution to the $\gamma \gamma h$ coupling is large and fairly constant up to the largest charged-Higgs mass allowed by tree-level unitarity bounds when the $b$-quark Yukawa coupling has the opposite sign from that of the SM (the change in sign of the interference terms between the $b$-quark loop and the $W$ and $t$ loops having negligible impact).

We extend the Standard Model (SM) by adding a pair of fermionic $SU(2)$ doublets with opposite hypercharge and a fermionic $SU(2)$ triplet with zero hypercharge. We impose a discrete $Z_2$ symmetry that distinguishes the SM fermions from the new ones. Then, gauge invariance allows for two renormalizable Yukawa couplings between the new fermions and the SM Higgs field, as well as for direct masses for the doublet ($M_D$) and the triplet ($M_T$). After electroweak symmetry breaking, this model contains, in addition to SM particles, two charged Dirac fermions and a set of three neutral Majorana fermions, the lightest of which contributes to dark matter (DM). We consider a case where the lightest neutral fermion is an equal admixture of the two doublets with mass $M_D$ close to the $Z$-boson mass. This state remains stable under radiative corrections thanks to a custodial $SU(2)$ symmetry and is consistent with the experimental data from oblique electroweak corrections. Moreover, the amplitudes relevant to spin-dependent or spin-independent nucleus-DM particle scattering cross sections both vanish at tree level. They arise at one loop at a level that may be observed in near future DM direct detection experiments. For Yukawa couplings comparable to the top quark, the DM particle relic abundance is consistent with observation, not relying on coannihilation or resonant effects, and has a mass at the electroweak scale. Furthermore, the heavier fermions decay to the DM particle and to electroweak gauge bosons making this model easily testable at the LHC. In the regime of interest, the charged fermions suppress the Higgs decays to diphotons by 45%–75% relative to SM prediction.

In this paper, we propose the study of the photoproduction of charmoniumlike states in $pp$ collisions at RHIC and LHC energies and estimate the rapidity distribution and total cross sections for the production of the exotic hadrons $Y(3940)$, $X(3915)$, $Z(4430)$, and $Z_c(3900)$. We demonstrate that the experimental analysis of this process can provide complementary and independent checks on these states and help to understand their underlying nature.

The sensitivities to anomalous quartic photon couplings at the Large Hadron Collider are estimated using diphoton production via photon fusion. The tagging of the protons proves to be a very powerful tool to suppress the background and unprecedented sensitivities down to $7\times 10^{-15}{\mathrm{GeV}}^{-4}$ are obtained, providing a new window on extra dimensions and strongly interacting composite states in the multi-TeV range. Generic contributions to quartic photon couplings from charged and neutral particles with arbitrary spin are also presented.

We study the production of charmed mesons ($D$, $D_s$) in antiproton-proton ($\overline{p}p$) annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on $\overline{p}p\to \overline{K}K$ by connecting the processes via SU(4) flavor symmetry. Our predictions for the $D\overline{D}$ production cross section are in the order of ${10}^{-2}-{10}^{-1}\mu b$. They turned out to be comparable to those obtained in other studies. The cross section for a $D_s^{+}{D}_s^{-}$ pair is found to be of the same order of magnitude despite the fact that its production in $\overline{p}p$ scattering requires a two-step process.

We study the uncertainties of the Higgs boson production cross section through the gluon fusion subprocess at the LHC (with $\sqrt{s}=7,8$, and 14 TeV) arising from the uncertainties of the parton distribution functions (PDFs) and of the value of the strong coupling constant ${\alpha }_s(M_Z)$. These uncertainties are computed by two complementary approaches based on the Hessian and the Lagrange multiplier methods within the CTEQ-TEA global analysis framework. We find that their predictions for the Higgs boson cross section are in good agreement. Furthermore, the result of the Lagrange multiplier method supports the prescriptions we have previously provided for using the Hessian method to calculate the combined PDF and ${\alpha }_s$ uncertainties, and to estimate the uncertainties at the 68% confidence level by scaling them from the 90% confidence level.

We present next-to-leading order predictions for the production of triphoton final states at the LHC and the Tevatron. Our results include the effect of photon fragmentation for the first time and we are able to quantify the impact of different isolation prescriptions. We find that calculations accounting for fragmentation effects at leading order, and those employing a smooth cone isolation where no fragmentation contribution is required, are in reasonable agreement with one another. However, larger differences in the predicted rates arise when higher order corrections to the fragmentation functions are included. In addition we present full analytic results for the $\gamma \gamma \gamma$ and $\gamma \gamma +\text{jet}$ one-loop amplitudes. These amplitudes, which are particularly compact, may be useful to future higher-order calculations. Our results are available in the Monte Carlo code mcfm.

We present a measurement of the $ZZ$-boson pair-production cross section in 1.96 TeV center-of-mass energy $p\overline{p}$ collisions. We reconstruct final states incorporating four charged leptons or two charged leptons and two neutrinos from the full data set collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity. Combining the results obtained from each final state, we measure a cross section of ${1.04}_{-0.25}^{+0.32}\mathrm{pb}$, in good agreement with the standard model prediction at next-to-leading order in the strong-interaction coupling.

In the present paper, we make a detailed analysis for the QCD corrections to the electroweak $\rho$ parameter by applying the principle of maximum conformality (PMC). As a comparison, we show that under the conventional scale setting, we have $\mathrm{\Delta }\rho {|}_{{\mathrm{N}}^3\mathrm{LO}}=(8.257_{-0.012}^{+0.045})\times {10}^{-3}$ by varying the scale ${\mu }_r\in [M_t/2,2M_t]$. By defining a ratio, $\mathrm{\Delta }R=\mathrm{\Delta }\rho /3X_t-1$, which shows the relative importance of the QCD corrections, it is found that its scale error is $\sim \pm 9\%$ at the two-loop level, which changes to $\sim \pm 4\%$ at the three-loop level, and $\sim \pm 2.5\%$ at the four-loop level, respectively. These facts well explain why the conventional scale uncertainty constitutes an important error for estimating the $\rho$ parameter. On the other hand, by applying the principle of maximum conformality scale setting, the four-loop estimation $\mathrm{\Delta }\rho {|}_{{\mathrm{N}}^3\mathrm{LO}}$ shall be almost fixed to $8.228\times {10}^{-3}$, which indicates that the conventional scale error has been eliminated. We observe that the pQCD convergence for the $\rho$ parameter has also been greatly improved due to the elimination of the divergent renormalon terms. As applications of the present QCD improved $\rho$ parameter, we show the shifts of the $W$-boson mass and the effective leptonic weak-mixing angle due to $\mathrm{\Delta }\rho$ can be reduced to $\delta M_W{|}_{{\mathrm{N}}^3\mathrm{LO}}=0.7\mathrm{MeV}$ and $\delta {\sin }^2{\theta }_{\text{eff}}{|}_{{\mathrm{N}}^3\mathrm{LO}}=-0.4\times {10}^{-5}$.

We study dark matter (DM) models in which there are two dark sector particles, ${\chi }_1$ and ${\chi }_2$, of near mass. In such models, co-annihilation of ${\chi }_1$ and ${\chi }_2$ may be the dominant process controlling the DM relic density during freeze-out in the early Universe. In this scenario, there is no significant contribution to direct and indirect detection signals, unless there exists an extreme degeneracy in the masses of the lightest dark sector particles. Therefore, relic density constraints and collider searches provide the most relevant information about these models. We consider Dirac fermion dark matter which couples to standard model (SM) particles via an effective operator. For the collider phenomenology, where an effective field theory may not be valid, we adopt a simple Z’ model to provide an appropriate UV completion. We explore the interesting LHC signals that arise from the dark matter production process $pp\to \overline{{\chi }_1}+{\chi }_2+\text{jet}$, followed by the decay ${\chi }_2\to {\chi }_1+\mathrm{SM}$.

We study jet substructures of a boosted polarized top quark, which undergoes the semileptonic decay $t\to b\ell \nu$, in the perturbative QCD framework. The jet mass distribution (energy profile) is factorized into the convolution of a hard top-quark decay kernel with the bottom-quark jet function (jet energy function). Computing the hard kernel to the leading order in QCD and inputting the latter functions from the resummation formalism, we observe that the jet mass distribution is not sensitive to the helicity of the top quark, but the energy profile is: energy is accumulated faster within a left-hand top jet than within a right-hand one, a feature related to the $V-A$ structure of weak interaction. It is pointed out that the energy profile is a simple and useful jet observable for helicity discrimination of a boosted top quark, which helps identification of physics beyond the standard model at the Large Hadron Collider. The extension of our analysis to other jet substructures, including those associated with a hadronically decaying polarized top quark, is proposed.

Based on the dual representation in terms of the recently established eigenfunctions of the evolution kernel in heavy-quark effective theory, we investigate the description of the $B$-meson light-cone distribution amplitude (LCDA) beyond tree level. In particular, in dual space, small and large momenta do not mix under renormalization, and therefore perturbative constraints from a short-distance expansion in the parton picture can be implemented independently from nonperturbative modelling of long-distance effects. It also allows us to (locally) resum perturbative logarithms from large dual momenta at fixed values of the renormalization scale. We construct a generic procedure to combine perturbative and nonperturbative information on the $B$-meson LCDA and compare different model functions and the resulting logarithmic moments which are the relevant hadronic parameters in QCD factorization theorems for exclusive $B$-meson decays.