We evaluate differential distributions for the four-body $pp\to pp{K}^{+}{K}^{-}$ reaction at high energies, which constitutes an irreducible background to three-body processes $pp\to ppM$, where $M=\varphi ,f_2(1275),f_0(1500),f_2^{\prime }(1525),{\chi }_{c0}$. We consider the central diffractive contribution mediated by Pomeron and Reggeon exchanges as well as a completely new mechanism of emission of kaons from the proton lines. We include absorption effects due to proton-proton interaction and kaon-kaon rescattering. We compare our results with measured cross sections for the CERN Intersecting Storage Rings experiment. We make predictions for future experiments at RHIC, Tevatron, and LHC. Differential distributions in invariant two-kaon mass, kaon rapidities, and transverse momenta of kaons are presented. Two-dimensional distribution in $(y_{K^{+}},y_{K^{-}})$ is particularly interesting. The higher the incident energy, the higher preference for the same-hemisphere emission of kaons. We find that the kaons from the new mechanism of emission directly from proton lines are produced rather forward and backward but the corresponding cross section is rather small. The processes considered here constitute a sizeable contribution to the total proton-proton cross section as well as to the kaon inclusive cross section. We consider a measurement of exclusive production of a scalar ${\chi }_{c0}$ meson in the proton-proton collisions via ${\chi }_{c0}\to K^{+}{K}^{-}$ decay. The corresponding amplitude for exclusive central diffractive ${\chi }_{c0}$ meson production is calculated within the $k_t$-factorization approach. The influence of kinematical cuts on the signal-to-background ratio is discussed.

As a top quark factory, the LHC can test new physics models used to explain the top quark forward-backward asymmetry $A_{\mathrm{FB}}^t$ measured at the Tevatron. In this work we perform a comparative study for two such models: the $W^{\prime }$ model and the color triplet diquark ($\varphi$) model. Requiring these models to explain $A_{\mathrm{FB}}^t$ and also satisfy the top pair production rate measured at the Tevatron, we examine their contributions to the LHC observables such as the polarizations and charge asymmetries in top quark productions and the charge asymmetry in $W^{\prime }$ (or $\varphi$) pair production. We find that these observables can be enhanced to their observable levels and current LHC measurement on the top charge asymmetry has already tightly constrained the $W^{\prime }$ model. We also find that each observable shows different characteristics in different models, which can be utilized to discriminate the models.

A simple renormalizable $U(1)$ gauge model is constructed to explain the smallness of the active neutrino masses and provide the stable cold dark matter candidate simultaneously. The local $U(1)$ symmetry is assumed to be spontaneously broken by a scalar field around the TeV scale. The active neutrino masses are then generated at one-loop level. This model contains several cold dark matter candidates whose stability is guaranteed by a residual discrete gauge $Z_2$ symmetry à la the Krauss-Wilczek mechanism. Unlike the other dark matter models, no further global discrete or continuous symmetry is introduced. Moreover, the masses of all fermionic degrees of freedom beyond the standard model are closely related to the scale of spontaneous breaking of $U(1)$; thus they could be probed at or below the TeV scale. The possible cosmological and phenomenological consequences are briefly discussed.

In this paper we derive Schwarzschild and Kerr-like noncommutative acoustic black hole metrics in the ($3+1$)-dimensional noncommutative Abelian Higgs model. We have found that the changing $\Delta T_{\mathrm{H}}$ in the Hawking temperature $T_{\mathrm{H}}$ due to spacetime noncommutativity accounts for supersonic velocities $v_g$, whose deviation with respect to the sound speed $c_s$ is given in the form $(v_g-c_s)/c_s=\Delta T_{\mathrm{H}}/8T_{\mathrm{H}}$.

One possibility for avoiding constraint violation in numerical relativity simulations adopting free-evolution schemes is to modify the continuum evolution equations so that constraint violations are damped away. Gundlach et al. demonstrated that such a scheme damps low-amplitude, high-frequency constraint-violating modes exponentially for the Z4 formulation of general relativity. Here we analyze the effect of the damping scheme in numerical applications on a conformal decomposition of Z4. After reproducing the theoretically predicted damping rates of constraint violations in the linear regime, we explore numerical solutions not covered by the theoretical analysis. In particular we examine the effect of the damping scheme on low-frequency and on high-amplitude perturbations of flat spacetime as well and on the long-term dynamics of puncture and compact star initial data in the context of spherical symmetry. We find that the damping scheme is effective provided that the constraint violation is resolved on the numerical grid. On grid noise the combination of artificial dissipation and damping helps to suppress constraint violations. We find that care must be taken in choosing the damping parameter in simulations of puncture black holes. Otherwise the damping scheme can cause undesirable growth of the constraints, and even qualitatively incorrect evolutions. In the numerical evolution of a compact static star we find that the choice of the damping parameter is even more delicate, but may lead to a small decrease of constraint violation. For a large range of values it results in unphysical behavior.

A supermassive black hole can disrupt a star when its tidal field exceeds the star’s self-gravity, and can directly capture stars that cross its event horizon. For black holes with mass $M\gtrsim {10}^7{M}_{\odot }$, tidal disruption of main-sequence stars occurs close enough to the event horizon that a Newtonian treatment of the tidal field is no longer valid. The fraction of stars that are directly captured is also no longer negligible. We calculate generically oriented stellar orbits in the Kerr metric, and evaluate the relativistic tidal tensor at the pericenter for those stars not directly captured by the black hole. We combine this relativistic analysis with previous calculations of how these orbits are populated to determine tidal-disruption rates for spinning black holes. We find, consistent with previous results, that black-hole spin increases the upper limit on the mass of a black hole capable of tidally disrupting solarlike stars to $\sim 7\times {10}^8{M}_{\odot }$. More quantitatively, we find that direct stellar capture reduces tidal-disruption rates by a factor $\sim 2/3(1/10)$ at $M\simeq {10}^7({10}^8)M_{\odot }$. The strong dependence of tidal-disruption rates on black-hole spin for $M\gtrsim {10}^8{M}_{\odot }$ implies that future surveys like the Large Synoptic Survey Telescope that discover thousands of tidal-disruption events can constrain supermassive black-hole spin demographics.

In this work we investigate the effect of a kind of scalar field, called chameleon, on the evolution of the Universe. We put this scalar field in the bulk. It is displayed that this scalar field gives us an exponential expansion in early time which may concern inflation. Interaction between the scalar field and matter brings some complications to our analysis; however, it is shown that by defining an effective potential, we could recover a conventional equation at the inflation era. After inflation, and entering the Universe in the radiation era, the exponential expansion is omitted. Also, in late time the Universe possesses an accelerated expansion. In the last section, the validity of the generalized second law of thermodynamics, with the assumption of the validity of the first law, is considered.

The use of Lagrange multipliers in the context of quintessence/phantom scalar fields allows us to constrain the behavior of the scalar field, which provides a powerful tool, not only for the reconstruction of cosmological solutions but also for the study of some problems in cosmology and gravitational physics. In the present paper, we focus on the reconstruction of cosmological solutions capable of controlling the cosmological constant value by imposing a constraint on the scalar field, providing a relaxation mechanism of the value of the cosmological constant. The formalism is also extended to the study of phantom scalar fields with a future singularity and their conformal transformation to the Jordan frame, where a type of modified gravity, constrained by the Lagrange multiplier, can be constructed.

A PNJL model is built, in which the Polyakov-loop potential is explicitly $Z_{N_c}$-symmetric in order to mimic a Yang-Mills theory with gauge group $\mathrm{SU}(N_c)$. The physically expected large-$N_c$ and large-$T$ behaviors of the thermodynamic observables computed from the Polyakov-loop potential are used to constrain its free parameters. The effective potential is eventually U(1)-symmetric when $N_c$ is infinite. Light quark flavours are added by using a Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (the PNJL model), and the different phases of the resulting PNJL model are discussed in ’t Hooft’s large-$N_c$ limit. Three phases are found, in agreement with previous studies resorting to effective approaches of QCD. When the temperature $T$ is larger than some deconfinement temperature $T_d$, the system is in a deconfined, chirally symmetric, phase for any quark chemical potential $\mu$. When $T<T_d$ however, the system is in a confined phase in which chiral symmetry is either broken or not. The critical line $T_{\chi }(\mu )$, signalling the restoration of chiral symmetry, has the same qualitative features than what can be obtained within a standard $N_c=3$ PNJL model.

In the framework of the large extra dimensions (LED) model, we investigate the effects induced by the Kaluza-Klein gravitons up to the QCD next-to-leading order (NLO) on the $W$-pair production followed by a subsequential $W$-decay at the CERN LHC. We depict the regions in the $\mathcal{L}-M_S$ parameter space where the LED effect can and cannot be observed from the analyses of the $pp\to W^{+}{W}^{-}+X$ and $pp\to W^{+}{W}^{-}\to W^{\pm }{l}^{\mp }\stackrel{(-)}{\nu }+X$ processes. We find that the ability of probing the LED effects can be improved by taking the cutoffs for the invariant mass of the $W$-pair and the transverse momentum of the final lepton. Our results demonstrate that the NLO QCD corrections to observables are significant, and do not show any improvement for the renormalization/factorization scale uncertainty on the QCD NLO corrected cross section, because the leading-order result underestimates the scale dependence.

The observation of jets in a variety of hard-scattering processes has allowed the quantitative study of perturbative quantum chromodynamics (PQCD) by comparing detailed theoretical predictions with a wide range of experimental data. This paper examines how some important, nonperturbative, facets of QCD involving the internal dynamical structure of jets can be studied by measuring the spin orientation of ${\Lambda }_0$ particles produced in these jets. The measurement of the transverse polarization for an individual ${\Lambda }_0$ within a QCD jet permits the definition of spin-directed asymmetries for quantum number densities in rapidity space (such as charge, strangeness and baryon number densities) involving neighboring hadrons in the jet. These asymmetries can only be generated by soft, nonperturbative dynamical mechanisms and such measurements can provide insight not otherwise accessible into the color rearrangement that occurs during the hadronization stage of fragmentation process.

The energy loss of hard jets produced in the deep-inelastic scattering off a large nucleus is considered in the collinear limit. In particular, the single gluon emission cross section due to multiple scattering in the medium is calculated. Calculations are carried out in the higher-twist scheme, which is extended to include contributions from multiple transverse scatterings on both the produced quark and the radiated gluon. The leading length-enhanced parts of these power suppressed contributions are resummed. Various interferences between such diagrams lead to the Landau-Pomeranchuk-Migdal effect. We resum the corrections from an arbitrary number of scatterings and isolate the leading contributions which are suppressed by one extra power of the hard scale $Q^2$. All powers of the emitted gluon forward momentum fraction $y$ are retained. We compare our results with the previous calculation of single scattering per emission in the higher-twist scheme as well as with multiple scattering resummations in other schemes. It is found that the leading ($1/Q^2$) contribution to the double differential gluon production cross section, in this approach, is equivalent to that obtained from the single scattering calculation once the transverse momentum of the final quark is integrated out. We comment on the generalization of this formalism to Monte Carlo routines.

We search for high-mass resonances decaying into $Z$ boson pairs using data corresponding to $6{\mathrm{fb}}^{-1}$ collected by the CDF experiment in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The search is performed in three distinct final states: $ZZ\to {\ell }^{+}{\ell }^{-}{\ell }^{+}{\ell }^{-}$, $ZZ\to {\ell }^{+}{\ell }^{-}\nu \nu$, and $ZZ\to {\ell }^{+}{\ell }^{-}jj$. For a Randall-Sundrum graviton $G^{*}$, the 95% CL upper limits on the production cross section times branching ratio to $ZZ$, $\sigma (p\overline{p}\to G^{*}\to ZZ)$, vary between 0.26 pb and 0.045 pb in the mass range $300<M_{G^{*}}<1000\mathrm{GeV}/c^2$.

A search is performed for heavy metastable particles that decay into jet pairs with a macroscopic lifetime ($c\tau \sim 1\mathrm{cm}$) in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using data from the CDF II detector at Fermilab corresponding to an integrated luminosity of $3.2{\mathrm{fb}}^{-1}$. To estimate the standard model background, a data-driven approach is used. Probability-density functions are constructed to model secondary vertices from known processes. No statistically significant excess is observed above the background. Limits on the production cross section in a hidden valley benchmark phenomenology are set for various Higgs boson masses as well as metastable particle masses and lifetimes.

We study the classical dynamics of $SU(2)$-Higgs field theory using multiple-scale perturbation theory. In the spontaneously broken phase, assuming small perturbations of the Higgs field around its vacuum expectation value, we derive a nonlinear Schrödinger equation and study the stability of its nonlinear plane wave solutions. The latter turn out to be stable only if the Higgs amplitude is an order of magnitude smaller than that of the gauge field. In this case, the Higgs field mass possesses some bounds which may be relevant to the search for the Higgs particle at ongoing experiments.

We study again the phenomenon of charge fractionalization at finite temperature. Our calculations are done in a framework in which the connection between the induced fermion number and the chiral anomaly is manifest. We find that the fractional fermion number induced on a soliton decreases as temperature rises and vanishes at infinite temperature at one-loop level. These results are consistent with previous studies. As an application of our approach, we have also studied the behavior of the induced Chern-Simons term in the ($2+1$)-dimensional QED at finite temperature.

We analyze the entanglement and the nonlocality of a ($1+1$)-dimensional massless Dirac field confined to a cavity on a world tube that consists of inertial and uniformly accelerated segments, for small accelerations but arbitrarily long travel times. The correlations between the accelerated field modes and the modes in an inertial reference cavity are periodic in the durations of the individual trajectory segments, and degradation of the correlations can be entirely avoided by fine-tuning the individual or relative durations of the segments. Analytic results for selected trajectories are presented. Differences from the corresponding bosonic correlations are identified, and extensions to massive fermions are discussed.

We discuss the notion of an effective, average, quantum mechanical path which is a solution of the dynamical equations obtained by extremizing the quantum effective action. Since the effective action can, in general, be complex, the effective path will also, in general, be complex. The imaginary part of the effective action is known to be related to the probability of particle creation by an external source and hence we expect the imaginary part of the effective path also to contain information about particle creation. We try to identify such features using simple examples including that of an effective path through the black hole horizon leading to thermal radiation. Implications of this approach are discussed.

In this paper we track the nonlinear spherical evolution of a massless scalar field onto a Schwarzschild black hole space-time as a first approximation to the accretion of cosmologically motivated classical scalar fields. We perform an analysis related to wave packets described by wave number and width. We study various values of the wave number $k$ and find that for $k=0$ and width packets bigger than the Schwarzschild radius, the absorption is not total. In the cases we study for $k>0$, the black hole absorbs the total amount of energy density of the scalar field moving toward the horizon. Our results indicate that assuming spherical symmetry in the nonlinear regime, there are cases for which scalar fields are allowed to survive outside black holes and may eventually have lifetimes consistent with cosmological time scales.

The motion of a (quasi-)plane wave in a uniform gravitational field is studied. It is shown that the energy of an elliptically polarized wave does not propagate along a geodesic, but in a direction that is rotated with respect to the gravitational force. The similarity with the walk-off effect in anisotropic crystals or the optical Magnus effect in inhomogeneous media is pointed out.