I present the resummation of collinear and soft-gluon corrections to single top quark production in the $t$ channel at next-to-next-to-leading logarithm accuracy using two-loop soft anomalous dimensions. The expansion of the resummed cross section yields approximate next-to-next-to-leading-order cross sections. Numerical results for $t$-channel single top quark (or single antitop) production at the Tevatron and the LHC are presented, including the dependence of the cross sections on the top quark mass and the uncertainties from scale variation and parton distributions. Combined results for all single top quark production channels are also given.

This article develops a computational framework for determining the location of boundary-covariant apparent horizons in the geometry of conformal fluid-gravity duality in arbitrary dimensions. In particular, it is shown up to second order and conjectured to hold to all orders in the gradient expansion that there is a unique apparent horizon which is covariantly expressible in terms of fluid velocity, temperature, and boundary metric. This leads to the first explicit example of an entropy current defined by an apparent horizon and opens the possibility that in the near-equilibrium regime there is preferred foliation of apparent horizons for black holes in asymptotically anti-de Sitter spacetimes.

In this work we analyze the localization of fermions on a brane embedded in five-dimensional, warped and nonwarped, space-time. In both cases we use the same nonlinear theoretical model with a nonpolynomial potential featuring a self-interacting scalar field whose minimum energy solution is a soliton (a kink) which can be continuously deformed into a two-kink. Thus a single brane splits into two branes. The behavior of spin $1/2$ fermions wave functions on the split brane depends on the coupling of fermions to the scalar field and on the geometry of the space-time.

Models with an extra dimension generally contain background scalar fields in a nontrivial configuration, whose stability must be ensured. With gravity present, the extra dimension is warped by the scalars, and the spin-0 degrees of freedom in the metric mix with the scalar perturbations. Where possible, we formally solve the coupled Schrödinger equations for the zero modes of these spin-0 perturbations. When specializing to the case of two scalars with a potential generated by a superpotential, we are able to fully solve the system. We show how these zero modes can be used to construct a solution matrix, whose eigenvalues tell whether a normalizable zero mode exists, and how many negative mass modes exist. These facts are crucial in determining stability of the corresponding background configuration. We provide examples of the general analysis for domain-wall models of an infinite extra dimension and domain-wall soft-wall models. For five-dimensional models with two scalars constructed using a superpotential, we show that a normalizable zero mode survives, even in the presence of warped gravity. Such models, which are widely used in the literature, are therefore phenomenologically unacceptable.

We explore the superhorizon generation of large $f_{\mathrm{NL}}$ of the local form in two-field inflation. We calculate the two- and three-point observables in a general class of potentials which allow for an analytic treatment using the $\delta N$ formalism. Motivated by the conservation of the curvature perturbation outside the horizon in the adiabatic mode and also by the observed adiabaticity of the power spectrum, we follow the evolution of $f_{\mathrm{NL}}^{\mathrm{local}}$ until it is driven into the adiabatic solution by passing through a phase of effectively single-field inflation. We find that, although large $f_{\mathrm{NL}}^{\mathrm{local}}$ may be generated during inflation, such nongaussianities are transitory and will be exponentially damped as the cosmological fluctuations approach adiabaticity.

If the lightest dark matter neutralino has a sufficiently large Higgsino component, its spin-independent and spin-dependent cross sections on nucleons can be sizable enough to be detected soon in direct and indirect surveys. We outline in this paper some characteristic features expected of mixed bino-Higgsino dark matter. If the observed relic density is saturated by the bino-Higgsino dark matter, it fixes the amount of allowable bino-Higgsino mixing and provides predictions for other observables which can be tested at the Large Hadron Collider (LHC). We study the correlation between the cross sections and the branching ratio of $B_s\to {\mu }^{+}{\mu }^{-}$. For a mixed bino-Higgsino dark matter, the mass differences of the neutralinos can be less than $M_Z$. This will cause an excess of lepton pairs, above the standard model predictions, from the decays of the two heavier neutralinos. We discuss implications of the dilepton invariant mass distribution, and outline a way to extract the neutralino parameters for testing gaugino mass unification and deducing the relic density from an interplay of astrophysical detection and LHC measurements.

The anomalously large like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays recently measured by the D0 Collaboration may be hinting at the presence of $CP$-violating new physics in the mixing of $B_s$ mesons. It has been suggested that the effect of a nonstandard spin-1 particle lighter than the $b$ quark with flavor-changing couplings to $b$ and $s$ quarks can reproduce the D0 result within its one-sigma range. Here we explore the possibility that the new particle also couples to charged leptons $\ell =e,\mu$ and thus contributes to rare $b\to s$ processes involving the leptons. We consider in particular constraints on its couplings from existing experimental data on the inclusive $B\to X_s{\ell }^{+}{\ell }^{-}$ and exclusive $B\to K^{(*)}{\ell }^{+}{\ell }^{-}$ decays, as well as the anomalous magnetic moments of the leptons. We find that there is parameter space of the particle that is allowed by the current data. We discuss how future measurements of these $B$ transitions and the rare decays of the $B_s$ meson, such as $B_s\to (\varphi ,\eta ,{\eta }^{\prime }){\ell }^{+}{\ell }^{-}$ and $B_s\to {\ell }^{+}{\ell }^{-}$, at LHCb and next-generation $B$ factories may probe its presence or couplings more stringently.

We work out the basic analysis on dynamics near the QCD critical point ($CP$) by the dynamic renormalization group (RG). In addition to the RG analysis by coarse-graining, we construct the nonlinear Langevin equation as a basic equation for the critical dynamics. Our construction is based on the generalized Langevin theory and the relativistic hydrodynamics. Applying the dynamic RG to the constructed equation, we derive the RG equation for the transport coefficients and analyze their critical behaviors. We find that the resulting RG equation turns out to be the same as that for the liquid-gas $CP$ except for an insignificant constant. Therefore, the bulk viscosity and the thermal conductivity strongly diverge at the QCD $CP$. We also show that the thermal and viscous diffusion modes exhibit critical slowing down with the dynamic critical exponents $z_{\mathrm{thermal}}\sim 3$ and $z_{\mathrm{viscous}}\sim 2$, respectively. In contrast, the sound propagating mode shows critical speeding up with the negative exponent $z_{\mathrm{sound}}\sim -0.8$.

Higgs bosons can be produced copiously at the LHC via gluon fusion induced by top and bottom quark loops, and can be enhanced strongly if extra heavy quarks exist. We present results for $\mathrm{\text{Higgs}}+\mathrm{\text{zero}}$-, one- and two-jet production at the LHC operating at 7 and 14 TeV collision energy, in both the standard model and the 4th generation model, by evaluating the corresponding heavy quark triangle, box, and pentagon Feynman diagrams. We compare the results by using the effective Higgs-gluon interactions in the limit of heavy quarks with the cross sections including the full mass dependences. NLO effects on $\mathrm{\text{Higgs}}+\mathrm{\text{zero}}$-jet production rate with full mass dependence are presented for the first time consistently in the 4th generation model. Our results improve the theoretical basis for fourth generation effects on the Higgs boson search at the LHC.

We provide a consistent description of the kinetic equation with a triangle anomaly which is compatible with the entropy principle of the second law of thermodynamics and the charge/energy-momentum conservation equations. In general an anomalous source term is necessary to ensure that the equations for the charge and energy-momentum conservation are satisfied and that the correction terms of distribution functions are compatible to these equations. The constraining equations from the entropy principle are derived for the anomaly-induced leading order corrections to the particle distribution functions. The correction terms can be determined for the minimum number of unknown coefficients in one charge and two charge cases by solving the constraining equations.

Light tensor mesons ($T=a_2$, $f_2$ and $K_2^{*}$) can be produced in decays of $\tau$ leptons. In this paper we compute the branching ratios of $\tau \to T\pi \nu$ decays by assuming the dominance of intermediate virtual states to model the form factors involved in the relevant hadronic matrix elements. The exclusive $f_2(1270){\pi }^{-}$ decay mode turns out to have the largest branching ratio, of $O({10}^{-4})$. Our results indicate that the contribution of tensor meson intermediate states to the three-pseudoscalar channels of $\tau$ decays are rather small.

We have investigated the existence of the $J^p=1/2^{+}$ narrow resonance predicted by the chiral soliton model by utilizing the kaon photoproduction process $\gamma +p\to K^{+}+\Lambda$. For this purpose we have constructed two phenomenological models based on our previous effective Lagrangian model, which are able to describe kaon photoproduction from threshold up to $W=1730\mathrm{MeV}$. By varying the mass (width) of an inserted $P_{11}$ resonance from 1620 to 1730 MeV (0.1 to 1 MeV and 1 to 10 MeV) a number of fits have been performed in order to search for the resonance mass. Our result indicates that the most promising candidate mass (width) of this resonance is 1650 MeV (5 MeV). Although our calculation does not exclude the possibility of narrow resonances with masses of 1680, 1700, and 1720 MeV, the mass of 1650 MeV is obtained for all phenomenological models used in this investigation. Variations of the resonance width and $K\Lambda$ branching ratio are found to have a mild effect on the ${\chi }^2$. The possibility that the obtained result originates from other resonance states is also discussed.

We study the effects of temporal UV-cutoff on the chiral critical surface in hot and dense QCD using a chiral effective model. Recent lattice QCD simulations indicate that the curvature of the critical surface might change toward the direction in which the first-order phase transition becomes stronger on increasing the number of lattice sites. To investigate this effect on the critical surface in an effective model approach, we use the Nambu–Jona-Lasinio model with finite Matsubara frequency summation. We find that the nature of the curvature of the critical surface does not alter appreciably as we decrease the summation number, which is unlike the case that was observed in recent lattice QCD studies. This may suggest that the dependence of chemical potential on the coupling strength or some additional interacting terms such as vector interactions could play an important role at finite density.

In minimal trinification models light neutrino masses can be generated via a radiative seesaw mechanism, where the masses of the right-handed neutrinos originate from loops involving Higgs and fermion fields at the unification scale. This mechanism is absent in models aiming at solving or ameliorating the hierarchy problem, such as low-energy supersymmetry, since the large seesaw scale disappears. In this case, neutrino masses need to be generated via a TeV-scale mechanism. In this paper, we investigate an inverse seesaw mechanism and discuss some phenomenological consequences.

Searches for $B$ mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either ${\Lambda }_c$ or $\Lambda$ and the lepton is a muon or an electron. These decays violate both baryon and lepton number and would be a signature of physics beyond the standard model. No significant signal is observed in any of the decay modes, and upper limits in the range $(3.2–520)\times {10}^{-8}$ are set on the branching fractions at the 90% confidence level.

We consider the effective potential $V$ in the standard model with a single Higgs doublet in the limit that the only mass scale $\mu$ present is radiatively generated. Using a technique that has been shown to determine $V$ completely in terms of the renormalization group (RG) functions when using the Coleman-Weinberg renormalization scheme, we first sum leading-log (LL) contributions to $V$ using the one loop RG functions, associated with five couplings (the top quark Yukawa coupling $x$, the quartic coupling of the Higgs field $y$, the $SU(3)$ gauge coupling $z$, and the $SU(2)\times U(1)$ couplings $r$ and $s$). We then employ the two loop RG functions with the three couplings $x$, $y$, $z$ to sum the next-to-leading-log (NLL) contributions to $V$ and then the three to five loop RG functions with one coupling $y$ to sum all the $N^{2}LL\dots N^{4}LL$ contributions to $V$. In order to compute these sums, it is necessary to convert those RG functions that have been originally computed explicitly in the minimal subtraction scheme to their form in the Coleman-Weinberg scheme. The Higgs mass can then be determined from the effective potential: the $LL$ result is $m_H=219\mathrm{GeV}/c^2$ and decreases to $m_H=188\mathrm{GeV}/c^2$ at $N^{2}LL$ order and $m_H=163\mathrm{GeV}/c^2$ at $N^{4}LL$ order. No reasonable estimate of $m_H$ can be made at orders $V_{NLL}$ or $V_{N^{3}LL}$ since the method employed gives either negative or imaginary values for the quartic scalar coupling. The fact that we get reasonable values for $m_H$ from the $LL$, $N^{2}LL$, and $N^{4}LL$ approximations is taken to be an indication that this mechanism for spontaneous symmetry breaking is in fact viable, though one in which there is slow convergence towards the actual value of $m_H$. The mass $163\mathrm{GeV}/c^2$ is argued to be an upper bound on $m_H$.

The inspiral and merger of a binary black hole system generally leads to an asymmetric distribution of emitted radiation, and hence a recoil of the remnant black hole directed opposite to the net linear momentum radiated. The recoil velocity is generally largest for comparable mass black holes and particular spin configurations, and approaches zero in the extreme mass ratio limit. It is generally believed that for extreme mass ratios $\eta \ll 1$, the scaling of the recoil velocity is $|\mathbf{V}|\propto {\eta }^2$, where the proportionality coefficient depends on the spin of the larger hole and the geometry of the system (e.g. orbital inclination). The small recoil velocity is due to cancellations; while the fraction of the total binary mass radiated away in gravitational waves is $O(\eta )$, most of this energy is emitted during the inspiral phase where the momentum radiated integrates to zero over an orbit. Here, we show that for low but nonzero inclination prograde orbits and very rapidly spinning large holes (spin parameter $a_{\star }>0.9678$) the inspiralling binary can pass through resonances where the orbit-averaged radiation-reaction force is nonzero. These resonance crossings lead to a new contribution to the kick, $|\mathbf{V}|\propto {\eta }^{3/2}$. For these configurations and sufficiently extreme mass ratios, this resonant recoil is dominant. While it seems doubtful that the resonant recoil will be astrophysically significant, its existence suggests caution when extrapolating the results of numerical kick results to extreme mass ratios and near-maximal spins.

We study nondegenerate and degenerate (extremal) Killing horizons of arbitrary geometry and topology within the Einstein-Maxwell-dilaton model with a Liouville potential (the EMdL model) in $d$-dimensional ($d\ge 4$) static space-times. Using Israel’s description of a static space-time, we construct the EMdL equations and the space-time curvature invariants: the Ricci scalar, the square of the Ricci tensor, and the Kretschmann scalar. Assuming that space-time metric functions and the model fields are real analytic functions in the vicinity of a space-time horizon, we study the behavior of the space-time metric and the fields near the horizon and derive relations between the space-time curvature invariants calculated on the horizon and geometric invariants of the horizon surface. The derived relations generalize similar relations known for horizons of static four- and five-dimensional vacuum and four-dimensional electrovacuum space-times. Our analysis shows that all the extremal horizon surfaces are Einstein spaces. We present the necessary conditions for the existence of static extremal horizons within the EMdL model.

The real time formalism at finite temperature and chemical potential for the nonlocal Nambu–Jona-Lasinio model is developed in the presence of a Gaussian covariant regulator. We construct the most general thermal propagator, by means of the spectral function. As a result, the model involves the propagation of massive quasiparticles. The appearance of complex poles is interpreted as a confinement signal, and, in this case, we have unstable quasiparticles with a finite decay width. An expression for the propagator along the critical line, where complex poles start to appear, is also obtained. A generalization to other covariant regulators is proposed.