We report on the calculation of the next-to-leading order QCD corrections to the production of $t\overline{t}$ pairs in association with two hard jets at the Fermilab Tevatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our next-to-leading order predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the Tevatron and 15% for the LHC. In the case of the Tevatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to ${\mathcal{A}}_{\mathrm{FB},\mathrm{LO}}^{\mathrm{t}}=-10.3\%$ at leading order and ${\mathcal{A}}_{\mathrm{FB},\mathrm{NLO}}^{\mathrm{t}}=-4.6\%$ at next-to-leading order. All results presented in this paper have been obtained with the help of the Helac-Nlo package.

The spontaneous breaking of chiral symmetry and the $U(1)$ axial anomaly in QCD can be phenomenologically understood by considering instantons as the gauge configurations mediating quark-quark interaction. The existence of an exact zero-mode solution of the Dirac equation in the field of a single instanton is the fundamental ingredient. Explicit expressions for ${\psi }_0$ are available for $T\ne 0$ and $\mu =0$, and $\mu \ne 0$ and $T=0$. In this paper we derive the solution for the most general case $T\ne 0$ and $\mu \ne 0$. This opens the possibility of investigating the QCD dynamics associated with instantons in the full phase diagram. As a first step in this direction, we will study the dependence of the instanton density from the thermodynamic coordinates.

Because of their small electromagnetic corrections, the isospin-breaking decays $\eta \to 3\pi$ seem to be good candidates for extracting isospin-breaking parameters $\sim (m_d-m_u)$. This task is unfortunately complicated by large chiral corrections and the discrepancy between the experimentally measured values of the Dalitz parameters describing the energy dependence of the amplitudes of these decays and those predicted from chiral perturbation theory. We present two methods based on an analytic dispersive representation that use the information from the NNLO chiral result and the one from the measurement of the charged $\eta \to 3\pi$ decay by KLOE together in a harmonized way in order to determine the value of the quark mass ratio $R$. Our final result is $R=37.7\pm 2.2$. This value supplemented by values of $m_s/\widehat{m}$ or even $\widehat{m}$ and $m_s$ from other methods (as sum-rules or lattice) enables us to obtain further quark mass characteristics. For instance the recent lattice value for $m_s/\widehat{m}\sim 27.5$ leads to $Q=23.1\pm 0.7$. We also quote the corresponding values of the current masses $m_u$ and $m_d$.

We consider central exclusive production of $gg$ dijets in proton-proton (proton-antiproton) collisions at LHC and Tevatron for different intermediate and final gluon polarizations. The amplitude for the process is derived within the $k_{\perp }$-factorization approach (with both the standard QCD and the Lipatov’s effective three-gluon vertices) and is considered in various kinematical asymptotia, in particular, in the important limit of high-$p_{\perp }$ jets. Compared to earlier works we include emissions of gluons from different gluonic $t$-channel lines as well as emission of quark-antiquark dijets. Rapidity distributions, gluon jet $p_{\perp }$ distributions and invariant dijet mass distributions are presented. We explore the competition of the standard diagram with both jets emitted from a single $t$-channel gluon and the one with the emission from both $t$-channel gluons. The second mechanism requires a special treatment. We propose two different approaches. Including special kinematics and using properties of off-diagonal gluons at small $x$ and $\xi$, we arrive to correlations in two-dimensional distributions in rapidity of one and second jet. We find that the second contribution is much smaller than that known from the literature. The digluon production constitutes an important background to exclusive Higgs production.

Recently the Belle collaboration discovered two resonances, $Z_b(10610)$ and $Z_b(10650)$, that lie very close to the $B{\overline{B}}^{*}$ and $B^{*}{\overline{B}}^{*}$ thresholds, respectively. It is natural to suppose that these are molecular states of bottom and antibottom mesons. Under this assumption, we introduce an effective field theory for the $Z_b(10610)$ and $Z_b(10650)$, as well as similar unobserved states that are expected on the basis of heavy quark spin symmetry. The molecules are assumed to arise from short-range interactions that respect heavy quark spin symmetry. We use the theory to calculate line shapes in the vicinity of $B^{(*)}{\overline{B}}^{(*)}$ thresholds as well as two-body decay rates of the new bottom meson bound states. We derive new heavy quark spin symmetry predictions for the parameters appearing in the line shapes as well as the total and partial widths of the states.

We calculate the single transverse spin asymmetry $A_N(t)$, for inclusive neutron production in $pp$ collisions at forward rapidities relative to the polarized proton in the energy range of RHIC. Absorptive corrections to the pion pole generate a relative phase between the spin-flip and nonflip amplitudes, leading to a transverse spin asymmetry which is found to be far too small to explain the magnitude of $A_N$ observed in the PHENIX experiment. A larger contribution, which does not vanish at high energies, comes from the interference of pion and $a_1$-Reggeon exchanges. The unnatural parity of $a_1$ guarantees a substantial phase shift, although the magnitude is strongly suppressed by the smallness of diffractive $\pi p\to a_{1}p$ cross section. We replace the Regge $a_1$ pole by the Regge cut corresponding to the $\pi \rho$ exchange in the $1^{+}S$ state. The production of such a state, which we treat as an effective pole $a$, forms a narrow peak in the $3\pi$ invariant mass distribution in diffractive $\pi p$ interactions. The cross section is large, so one can assume that this state saturates the spectral function of the axial current and we can determine its coupling to nucleons via the partially conserved axial-vector-current constraint Goldberger-Treiman relation and the second Weinberg sum rule. The numerical results of the parameter-free calculation of $A_N$ are in excellent agreement with the PHENIX data.

In this paper we study nonstandard neutrino interactions as an example of physics beyond the standard model using atmospheric neutrino data collected during the Super-Kamiokande I (1996–2001) and II (2003–2005) periods. We focus on flavor-changing-neutral-currents (FCNC), which allow neutrino flavor transitions via neutral current interactions, and effects which violate lepton nonuniversality and give rise to different neutral-current interaction-amplitudes for different neutrino flavors. We obtain a limit on the FCNC coupling parameter, ${\epsilon }_{\mu \tau }$, $|{\epsilon }_{\mu \tau }|<1.1\times {10}^{-2}$ at 90% C.L. and various constraints on other FCNC parameters as a function of the nonuniversality coupling, ${\epsilon }_{ee}$. We find no evidence of nonstandard neutrino interactions in the Super-Kamiokande atmospheric data.

Harrison, Perkins and Scott have proposed simple charged lepton and neutrino mass matrices that lead to the tribimaximal mixing $U_{\mathrm{TBM}}$. We consider in this work an extension of the mass matrices so that the leptonic mixing matrix becomes $U_{\mathrm{PMNS}}=V_L^{\ell †}{U}_{\mathrm{TBM}}W$, where $V_L^{\ell }$ is a unitary matrix needed to diagonalize the charged lepton mass matrix and $W$ measures the deviation of the neutrino mixing matrix from the bimaximal form. Hence, corrections to $U_{\mathrm{TBM}}$ arise from both charged lepton and neutrino sectors. Following our previous work to assume a Qin-Ma-like parametrization $V_{\mathrm{QM}}$ for the charged lepton mixing matrix $V_L^{\ell }$ in which the $CP$-odd phase is approximately maximal, we study the phenomenological implications in two different scenarios: $V_L^{\ell }=V_{\mathrm{QM}}^{†}$ and $V_L^{\ell }=V_{\mathrm{QM}}$. We find that the latter is more preferable, though both scenarios are consistent with the data within $3\sigma$ ranges. The predicted reactor neutrino mixing angle ${\theta }_{13}$ in both scenarios is consistent with the recent T2K and MINOS data. The leptonic $CP$ violation characterized by the Jarlskog invariant $J$ is generally of order ${10}^{-2}$.

The $Z\to \tau \tau$ cross section is measured with the ATLAS experiment at the LHC in four different final states determined by the decay modes of the $\tau$ leptons: muon-hadron, electron-hadron, electron-muon, and muon-muon. The analysis is based on a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$, at a proton-proton center-of-mass energy of $\sqrt{s}=7\mathrm{TeV}$. Cross sections are measured separately for each final state in fiducial regions of high detector acceptance, as well as in the full phase space, over the mass region 66–116 GeV. The individual cross sections are combined and the product of the total $Z$ production cross section and $Z\to \tau \tau$ branching fraction is measured to be $0.97\pm 0.07(\mathrm{stat})\pm 0.06(\mathrm{syst})\pm 0.03(\mathrm{lumi})\mathrm{nb}$, in agreement with next-to-next-to-leading order calculations.

We report on the high statistics two-pion correlation functions from $pp$ collisions at $\sqrt{s}=0.9\mathrm{TeV}$ and $\sqrt{s}=7\mathrm{TeV}$, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of “mini-jet”-like structures extending to low $p_t$. They are well reproduced by the Monte-Carlo generators and seen also in ${\pi }^{+}{\pi }^{-}$ correlations.

We investigate the scalar perturbations in an anti-de Sitter soliton background coupled to a Maxwell field via marginally stable modes. In the probe limit, we study the magnetic field effect on the holographic insulator/superconductor phase transition numerically and analytically. The condensate will be localized in a finite circular region for any finite constant magnetic field. Near the critical point, we find that there exists a simple relation among the critical chemical potential, magnetic field, the charge, and mass of the scalar field. This relation indicates that the presence of the magnetic field causes the transition from insulator to superconductor to be difficult.

Physical effects in brane world models emerge by the incorporation of field modes coming from extra dimensions with the usual four-dimensional ones. Such effects can be tested with well-established experiments to set bounds on the parameters of the brane models. In this work we extend a previous result which gave finite electromagnetic potentials and self-energies for a source looking pointlike to an observer sitting in a 4D Minkowski subspace of a single brane of a Randall-Sundrum spacetime including compact dimensions, and along which the source stretches uniformly. We show that a scalar particle produces a nonsingular static potential, possesses a finite self-energy, and that technically its analysis is very similar to the electrostatic case. As for the latter, we use the deviations from the Coulomb potential to set bounds on the anti–de Sitter radius of the brane model on the basis of two experiments, namely, one of the Cavendish type and the other being the scattering of electrons by helium atoms. We found these are less stringent than others previously obtained using the Lamb shift in hydrogen.

In this paper, we investigate the recently developed lattice Boltzmann model for relativistic hydrodynamics. To this purpose, we perform simulations of shock waves in quark-gluon plasma in the low and high viscosities regime, using three different computational models, the relativistic lattice Boltzmann (RLB), the Boltzmann Approach Multi-Parton Scattering (BAMPS), and the viscous sharp and smooth transport algorithm (vSHASTA). From the results, we conclude that the RLB model departs from BAMPS in the case of high speeds and high temperature (viscosities), the departure being due to the fact that the RLB is based on a quadratic approximation of the Maxwell-Jüttner distribution, which is only valid for sufficiently low temperature and velocity. Furthermore, we have investigated the influence of the lattice speed on the results, and shown that inclusion of quadratic terms in the equilibrium distribution improves the stability of the method within its domain of applicability. Finally, we assess the viability of the RLB model in the various parameter regimes relevant to ultrarelativistic fluid dynamics.

We construct a new static spherically symmetric configuration composed of interior and exterior Brans-Dicke vacua matched at a thin matter shell. Both vacua correspond to the same Brans-Dicke coupling parameter $\omega$; however, they are described by the Brans class I solution with different sets of parameters of integration. In particular, the exterior vacuum solution has $C_{\mathrm{ext}}(\omega )\equiv 0$. In this case the Brans class I solution for any $\omega$ reduces to the Schwarzschild one being consistent with restrictions on the post-Newtonian parameters following from recent Cassini data. The interior region possesses a strong gravitational field, and so the interior vacuum solution has $C_{\mathrm{int}}(\omega )=-1/(\omega +2)$. In this case the Brans class I solution describes a wormhole spacetime provided $\omega$ lies in the narrow interval $-2-\frac{\sqrt{3}}{3}<\omega <-2$. The interior and exterior regions are matched at a thin shell made from an ordinary perfect fluid with positive energy density and pressure obeying the barotropic equation of state $p=k\sigma$ with $0\le k\le 1$. The resulting configuration represents a composite wormhole, i.e. the thin matter shell with the Schwarzschild-like exterior region and the interior region containing the wormhole throat.

The discovery of the unexpected dimness of type Ia supernovae, apparently due to accelerated expansion driven by some form of dark energy or modified gravity, has led to attempts to explain the observations using only general relativity with baryonic and cold dark matter, but by dropping the standard assumption of homogeneity on Hubble scales. In particular, the supernova data can be explained if we live near the center of a Hubble-scale void. However, such void models have been shown to be inconsistent with various observations, assuming the void consists of a pure growing mode. Here it is shown that models with significant decaying mode contribution today can be ruled out on the basis of the expected cosmic microwave background spectral distortion. This essentially closes one of the very few remaining loopholes in attempts to rule out void models, and strengthens the evidence for Hubble-scale homogeneity.

Volume modifications to the binding of two-body systems in large cubic volumes of extent $L$ depend upon the total momentum and exponentially upon the ratio of $L$ to the size of the boosted system. Recent work by Bour et al. determined the momentum dependence of the leading volume modifications to nonrelativistic systems with periodic boundary conditions imposed on the single-particle wave functions, enabling them to numerically determine the scattering of such bound states using a low-energy effective field theory and Lüscher’s finite-volume method. The calculation of bound nuclear systems directly from QCD using lattice QCD has begun, and it is important to reduce the systematic uncertainty introduced into such calculations by the finite spatial extent of the gauge-field configurations. We extend the work of Bour et al. from nonrelativistic quantum mechanics to quantum field theory by generalizing the work of Lüscher and of Gottlieb and Rummukainen to boosted two-body bound states. The volume modifications to binding energies can be exponentially reduced from $\mathcal{O}(e^{-\kappa L}/L)$ to $\mathcal{O}(e^{-2\kappa L}/L)$ in nonrelativistic systems (where $\kappa$ is the binding momentum of the state) by forming particular combinations of the binding energies determined in the four lowest-lying boosted systems. Relativistic corrections to this combination, and others, that violate the exponential reduction are determined. An analysis of what can be expected from lattice QCD calculations of the deuteron is performed, the results of which are representative of a generic loosely bound system.

We present a new framework for the extraction of the strong coupling from hadronic $\tau$ decays through finite-energy sum rules. Our focus is on the small, but still significant nonperturbative effects that, in principle, affect both the central value and the systematic error. We employ a quantitative model in order to accommodate violations of quark-hadron duality, and enforce a consistent treatment of the higher-dimensional contributions of the operator product expansion to our sum rules. Using 1998 OPAL data for the nonstrange isovector vector and axial-vector spectral functions, we find the $n_f=3$ values ${\alpha }_s(m_{\tau }^2)=0.307\pm 0.019$ in fixed-order perturbation theory, and $0.322\pm 0.026$ in contour-improved perturbation theory. For comparison, the original OPAL analysis of the same data led to the values $0.324\pm 0.014$ (fixed order) and $0.348\pm 0.021$ (contour improved).

We have studied a $(1+2)$-dimensional Lorentz-violating model which is obtained from the dimensional reduction of the nonbirefringent sector of the $CPT$-even electrodynamics of the standard model extension. The planar theory contains a gauge sector and a scalar sector which are linearly coupled by means of a Lorentz-invariance violating (LIV) vector, $S^{\mu }$, while the kinetic terms of both sectors are affected by the components of a Lorentz-violating symmetric tensor, ${\kappa }^{\mu \nu }$. The energy-momentum tensor reveals that both sectors present energy stability for sufficiently small values of the Lorentz-violating parameters. The full dispersion relation equations are exactly determined and analyzed for some special configurations of the LIV backgrounds, showing that the planar model is entirely nonbirefringent at any order in the LIV parameters. At first order, the gauge and scalar sectors are described by the same dispersion relations. Finally, the equations of motion have been solved in the stationary regime and at first order in the LIV parameters. It is observed that the Lorentz-violating parameters do not alter the asymptotical behavior of the electric and magnetic fields but induce an angular dependence which is not present in Maxwell’s planar theory.

In three spacetime dimensions, the world volume of a magnetic source is a single point, a magnetically charged event. It has been shown long ago that in three-dimensional spacetime, the Chern-Simons coupling is quantized, because the magnetic event emits an electric charge which must be quantized according to the standard Dirac rule. Recently, the concept of dynamical extended charged events has been introduced, and it has been argued that they should play as central a role as that played by particles or ordinary branes. In this article, we show that in the presence of a Chern-Simons coupling, a magnetically charged extended event emits an extended object, which geometrically is just like a Dirac string, but it is observable, obeys equations of motion, and may be electrically charged. We write a complete action principle which accounts for this effect. The action involves two Chern-Simons terms, one integrated over spacetime and the other integrated over the world volume of the submanifold that is the union of the Dirac world sheet and the history of the emitted physical object. By demanding that the total charge emitted by a composite extended magnetic event be quantized according to Dirac’s rule, we find a quantization condition for the Chern-Simons coupling. For a 1-form electric potential in $D=2n+1$ spacetime dimensions, the composite event is formed by $n$ elementary extended magnetic events separated in time such that the product of their transverse spaces, together with the time axis, is the entire spacetime. We show that the emitted electric charge is given by the integral of the ($n-1$)-th exterior power of the electromagnetic field strength over the last elementary event, or, equivalently, over an appropriate closed surface. The extension to more general $p$-form potentials and higher dimensions is also discussed. For the case $D=11$, $p=3$, our result for the quantization of the Chern-Simons coupling was obtained previously in the context of M theory, an agreement that makes the existence of extended charged events all the more cogent.

The bubble wall velocity in an electroweak first order phase transition is a key quantity both for electroweak baryogenesis and for the production of a stochastic background of gravitational waves that may be probed in the future through gravitational wave experiments like LISA or BBO. We show that, contrary to the conclusion drawn from previous studies, it is actually possible to generate a potentially large gravitational wave signal while satisfying the requirements for viable electroweak baryogenesis, once the effects of the hydrodynamics of bubble growth are taken into account. Then, the observation of a large gravitational wave background from the electroweak phase transition would not necessarily rule out electroweak baryogenesis as the mechanism having generated the observed baryon asymmetry of the Universe.