The Drell-Yan mechanism for the production of lepton pairs is one of the most basic processes for physics studies at hadron colliders. It is therefore important to have accurate theoretical predictions. In this work we compute the two-loop virtual mixed $\mathrm{QCD}\times \mathrm{QED}$ corrections to Drell-Yan production. We evaluate the Feynman diagrams by decomposing the amplitudes into a set of known master integrals and their coefficients, which allows us to derive an analytical result. We also perform a detailed study of the ultraviolet and infrared structure of the two-loop amplitude and the corresponding poles in $\epsilon$. Using crossing symmetry, we also determine the corresponding two-loop result for deep inelastic scattering.

We show a TeV-scale seesaw model where Majorana neutrino masses, the dark matter mass, and stability of the dark matter can be all originated from the $U(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by $U(1{)}_{\mathrm{B}-\mathrm{L}}$, and they are induced at the one-loop level by spontaneous $U(1{)}_{\mathrm{B}-\mathrm{L}}$ breaking. The right-handed neutrinos can be naturally at the TeV scale or below because of the induced Dirac mass terms with loop suppression. Such right-handed neutrinos would be discovered at the CERN Large Hadron Collider. On the other hand, stability of the dark matter is guaranteed without introducing an additional $Z_2$ symmetry by a remaining global $U(1)$ symmetry after the $U(1{)}_{\mathrm{B}-\mathrm{L}}$ breaking. A Dirac fermion ${\Psi }_1$ or a complex neutral scalar $s_1^0$ is the dark matter candidate in this model. Since the dark matter (${\Psi }_1$ or $s_1^0$) has its own $\mathrm{B}-\mathrm{L}$ charge, the invisible decay of the $U(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge boson $Z^{\prime }$ is enhanced. Experimental constraints on the model are considered, and the collider phenomenology at the LHC as well as future linear colliders is discussed briefly.

We study supersymmetric structure of the self-isospectral crystalline chains formed by $N$ copies of the mutually displaced one-gap Lamé systems. It is generated by the $N(N-1)$ integrals of motion which are the first order matrix differential operators, by the same number of the nontrivial second order integrals, and by the $N$ third order Lax integrals. We show that the structure admits distinct alternatives for a grading operator, and in dependence on its choice one of the third order matrix integrals plays either the role of the bosonic central charge or the role of the fermionic supercharge to be a square root of the spectral polynomial. Yet another peculiarity is that the set of all the second order integrals of motion generates a nonlinear sub-superalgebra. We also investigate the associated self-isospectral soliton chains, and discuss possible physical applications of the unusual extended supersymmetry.

We show how to compute the coefficients of the double-box basis integrals in a massless four-point amplitude in terms of tree amplitudes. We show how to choose suitable multidimensional contours for performing the required cuts, and derive consistency equations from the requirement that integrals of total derivatives vanish. Our formulas for the coefficients can be used either analytically or numerically.

We adapt a method of matching post-Newtonian and black-hole-perturbation theories on a timelike surface (which proved useful for understanding head-on black-hole-binary collisions) to treat equal-mass, inspiralling black-hole binaries. We first introduce a radiation-reaction potential into this method, and we show that it leads to a self-consistent set of equations that describe the simultaneous evolution of the waveform and of the timelike matching surface. This allows us to produce a full inspiral-merger-ringdown waveform of the $l=2$, $m=\pm 2$ modes of the gravitational waveform of an equal-mass black-hole-binary inspiral. These modes match those of numerical-relativity simulations well in phase, though less well in amplitude for the inspiral. As a second application of this method, we study a merger of black holes with spins antialigned in the orbital plane (the superkick configuration). During the ringdown of the superkick, the phases of the mass- and current-quadrupole radiation become locked together, because they evolve at the same quasinormal-mode frequencies. We argue that this locking begins during the merger, and we show that if the spins of the black holes evolve via geodetic precession in the perturbed black-hole spacetime of our model, then the spins precess at the orbital frequency during the merger. In turn, this gives rise to the correct behavior of the radiation, and produces a kick similar to that observed in numerical simulations.

We extend the discrete Regge action of causal dynamical triangulations to include discrete versions of the curvature squared terms appearing in the continuum action of $(2+1)$-dimensional projectable Hořava-Lifshitz gravity. Focusing on an ensemble of spacetimes whose spacelike hypersurfaces are two-spheres, we employ Markov chain Monte Carlo simulations to study the path integral defined by this extended discrete action. We demonstrate the existence of known and novel macroscopic phases of spacetime geometry, and we present preliminary evidence for the consistency of these phases with solutions to the equations of motion of classical Hořava-Lifshitz gravity. Apparently, the phase diagram contains a phase transition between a time-dependent de Sitter-like phase and a time-independent phase. We speculate that this phase transition may be understood in terms of deconfinement of the global gravitational Hamiltonian integrated over a spatial two-sphere.

Three dark matter direct detection experiments (DAMA/LIBRA, CoGeNT, and CRESST-II) have each reported signals which are not consistent with known backgrounds, but resemble that predicted for a dark matter particle with a mass of roughly $\sim 10\mathrm{GeV}$ and an elastic scattering cross section with nucleons of $\sim {10}^{-41}–{10}^{-40}{\mathrm{cm}}^2$. In this article, we compare the signals of these experiments and discuss whether they can be explained by a single species of dark matter particle, without conflicting with the constraints of other experiments. We find that the spectrum of events reported by CoGeNT and CRESST-II are consistent with each other and with the constraints from CDMS-II, although some tension with xenon-based experiments remains. Similarly, the modulation signals reported by DAMA/LIBRA and CoGeNT appear to be compatible, although the corresponding amplitude of the observed modulations are a factor of at least a few higher than would be naively expected, based on the event spectra reported by CoGeNT and CRESST-II. This apparent discrepancy could potentially be resolved if tidal streams or other non-Maxwellian structures are present in the local distribution of dark matter.

We derive general and explicit expressions for the unrenormalized and renormalized dressed propagators of fermions in parity-nonconserving theories with intergeneration mixing. The mass eigenvalues, the corresponding mass counterterms, and the effect of intergeneration mixing on their determination are discussed. Invoking the Aoki-Hioki-Kawabe-Konuma-Muta renormalization conditions and employing a number of very useful relations from matrix algebra, we show explicitly that the renormalized dressed propagators satisfy important physical properties.

We analyze $F_{\pi }(Q^2)$ and $F_{P\gamma }(Q^2)$, $P=\pi$, $\eta$, ${\eta }^{\prime }$, within the local-duality (LD) version of QCD sum rules, which allows one to obtain predictions for hadron form factors in a broad range of momentum transfers. To probe the accuracy of this approximate method, we consider, in parallel to QCD, a potential model: in this case, the exact form factors may be calculated from the solutions of the Schrödinger equation and confronted with the results from the quantum-mechanical LD sum rule. On the basis of our quantum-mechanical analysis we conclude that the LD sum rule is expected to give reliable predictions for $F_{\pi }(Q^2)$ and $F_{\pi \gamma }(Q^2)$ in the region $Q^2\ge 5–6{\mathrm{GeV}}^2$. Moreover, the accuracy of the method improves rather fast with growing $Q^2$ in this region. For the pion elastic form factor, the data at small $Q^2$ indicate that the LD limit may be reached already at relatively low values of momentum transfers, $Q^2\approx 4–8{\mathrm{GeV}}^2$; we therefore conclude that large deviations from LD in the region $Q^2=20–50{\mathrm{GeV}}^2$ reported in some recent theoretical analyses seem unlikely. The data on the $(\eta ,{\eta }^{\prime })\to \gamma {\gamma }^{*}$ form factors meet very well the expectations from the LD model. Surprisingly, the BABAR results for the ${\pi }^0\to \gamma {\gamma }^{*}$ form factor imply a violation of LD growing with $Q^2$ even at $Q^2\approx 40{\mathrm{GeV}}^2$, at odds with the $\eta$, ${\eta }^{\prime }$ case and the experience from quantum mechanics.

We consider the vertex function of two vector and one axial-vector currents using the soft-wall holographic model of QCD with the Chern-Simons term. Two structure functions $w_L$ and $w_T$ describe such a vertex in the special case in which one of the two vector currents corresponds to an on-shell soft photon. We briefly review the QCD results for these functions, obtained from triangular loop diagrams with quarks having mass $m_q=0$ or $m_q\ne 0$, we compute $w_L$ and $w_T$ in the soft-wall model and compare the outcome to the QCD findings. We also calculate and discuss the two-point ${\Pi }_{VV}-{\Pi }_{AA}$ correlation function, together with a few low-energy constants, which turn out to be close to the QCD results. Finally, we comment on a relation proposed by Son and Yamamoto between $w_T$ and ${\Pi }_{VV}-{\Pi }_{AA}$.

We report an analysis of the ${\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ decay in a data sample collected by the CDF II detector at the Fermilab Tevatron corresponding to $2.4{\mathrm{fb}}^{-1}$ of integrated luminosity. We reconstruct the currently largest samples of the decay modes ${\Lambda }_b^0\to {\Lambda }_c(2595{)}^{+}{\pi }^{-}$ (with ${\Lambda }_c(2595{)}^{+}\to {\Lambda }_c^{+}{\pi }^{+}{\pi }^{-}$), ${\Lambda }_b^0\to {\Lambda }_c(2625{)}^{+}{\pi }^{-}$ (with ${\Lambda }_c(2625{)}^{+}\to {\Lambda }_c^{+}{\pi }^{+}{\pi }^{-}$), ${\Lambda }_b^0\to {\Sigma }_c(2455{)}^{++}{\pi }^{-}{\pi }^{-}$ (with ${\Sigma }_c(2455{)}^{++}\to {\Lambda }_c^{+}{\pi }^{+}$), and ${\Lambda }_b^0\to {\Sigma }_c(2455{)}^0{\pi }^{+}{\pi }^{-}$ (with ${\Sigma }_c(2455{)}^0\to {\Lambda }_c^{+}{\pi }^{-}$) and measure the branching fractions relative to the ${\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}$ branching fraction. We measure the ratio $\mathcal{B}({\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})/\mathcal{B}({\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-})=3.04\pm 0.33(\mathrm{stat}{)}_{-0.55}^{+0.70}(\mathrm{syst})$ which is used to derive $\mathcal{B}({\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})=({26.8}_{-11.2}^{+11.9})\times {10}^{-3}$.

We report a search for $CP$ violation in the decay ${\tau }^{-}\to {\pi }^{-}{K}_S^0(\ge 0{\pi }^0){\nu }_{\tau }$ using a data set of $437\times {10}^6$ $\tau$-lepton pairs, corresponding to an integrated luminosity of $476{\mathrm{fb}}^{-1}$, collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage rings. The $CP$-violating decay-rate asymmetry is determined to be $(-0.36\pm 0.23\pm 0.11)\%$ approximately 2.8 standard deviations from the standard model prediction of $(0.36\pm 0.01)\%$.

The vacuum expectation value (VEV) of the energy-momentum tensor for a massive fermionic field is investigated in a ($2+1$)-dimensional conical spacetime in the presence of a circular boundary and an infinitely thin magnetic flux located at the cone apex. The MIT bag boundary condition is assumed on the circle. At the cone apex we consider a special case of boundary conditions for irregular modes, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. The presence of the magnetic flux leads to the Aharonov-Bohm-like effect on the VEV of the energy-momentum tensor. For both exterior and interior regions, the VEV is decomposed into boundary-free and boundary-induced parts. Both these parts are even periodic functions of the magnetic flux with the period equal to the flux quantum. The boundary-free part in the radial stress is equal to the energy density. Near the circle, the boundary-induced part in the VEV dominates and for a massless field the vacuum energy density is negative inside the circle and positive in the exterior region. Various special cases are considered.

Starting from a low energy effective chiral Lagrangian with a gauged Wess-Zumino-Witten term, we have derived a hydrodynamic theory for chiral superfluid. It is a non-Abelian hydrodynamics at zero temperature with only superfluid components. With an external electromagnetic field and baryonic and axial baryonic chemical potentials turned on, we are able to identify analogs of various anomaly induced terms in normal hydrodynamics, including a chiral vortical effect, a chiral magnetic effect, and a chiral electric effect. As an example, we solved the hydrodynamic equations for the ground state and observed the chiral magnetic effect and chiral separation in the confined phase.

In this paper we consider some aspects of the relativistic dynamics of a cylindrical shell of counterrotating particles. In some sense these are the simplest systems with a physically acceptable matter content that display in a well-defined sense an interaction with the radiative modes of the gravitational field. These systems have been analyzed previously, but in most cases resorting to approximations, or considering a particular form for the initial value data. Here we show that there exists a family of solutions where the space time inside the shell is flat and the equation of motion of the shell decouples completely from the gravitational modes. The motion of the shell is governed by an equation of the same form as that of a particle in a time-independent one-dimensional potential. We find that under appropriate initial conditions one can have collapsing, bounded periodic, and unbounded motions. We analyze and solve also the linearized equations that describe the dynamics of the system near a stable static solutions, keeping a regular interior. The surprising result here is that the motion of the shell is completely determined by the configuration of the radiative modes of the gravitational field. In particular, there are oscillating solutions for any chosen period, in contrast with the “approximately Newtonian plus small radiative corrections” motion expectation. We comment on the physical meaning of these results and provide some explicit examples. We also discuss the relation of our results to the initial value problem for the linearized dynamics of the shell.

We propose, within the effective-one-body approach, a new, resummed analytical representation of the gravitational-wave energy flux absorbed by a system of two circularized (nonspinning) black holes. This expression is such that it is well-behaved in the strong-field, fast-motion regime, notably up to the effective-one-body-defined last unstable orbit. Building conceptually upon the procedure adopted to resum the multipolar asymptotic energy flux, we introduce a multiplicative decomposition of the multipolar absorbed flux made by three factors: (i) the leading-order contribution, (ii) an “effective source” and (iii) a new residual amplitude correction $({\tilde{\rho }}_{\ell m}^H{)}^{2\ell }$. In the test-mass limit, we use a frequency-domain perturbative approach to accurately compute numerically the horizon-absorbed fluxes along a sequence of stable and unstable circular orbits, and we extract from them the functions ${\tilde{\rho }}_{\ell m}^H$. These quantities are then fitted via rational functions. The resulting analytically represented test-mass knowledge is then suitably hybridized with lower-order analytical information that is valid for any mass ratio. This yields a resummed representation of the absorbed flux for a generic, circularized, nonspinning black-hole binary. Our result adds new information to the state-of-the-art calculation of the absorbed flux at fractional 5 post-Newtonian order [S. Taylor and E. Poisson, Phys. Rev. D 78, 084016 (2008)], which is recovered in the weak-field limit approximation by construction.

In massive gravity, the black hole solutions found so far on Minkowski space happen to convert horizons into a certain type of singularities. Here, we explore whether these singularities can be avoided if space-time is not asymptotically Minkowskian. We find an exact analytic black hole (BH) solution, which evades the above problem by a transition at large scales to self-induced de Sitter space-time, with the curvature scale set by the graviton mass. This solution is similar to the ones discovered by Koyama, Niz, and Tasinato, and by Nieuwenhuizen, but differs in detail. The solution demonstrates that in massive general relativity, in the Schwarzschild coordinate system, a BH metric has to be accompanied by the Stückelberg fields with nontrivial backgrounds to prevent the horizons to convert into the singularities. We also find an analogous solution for a Reissner-Nordström BH on de Sitter space. A limitation of our approach is that we find the solutions only for specific values of the two free parameters of the theory, for which both the vector and scalar fluctuations lose their kinetic terms; however, we hope our solutions represent a broader class with better-behaved perturbations.

The fully constrained formulation (FCF) of general relativity is a framework introduced as an alternative to the hyperbolic formulations traditionally used in numerical relativity. The FCF equations form a hybrid elliptic-hyperbolic system of equations including explicitly the constraints. We present an implicit-explicit numerical algorithm to solve the hyperbolic part, whereas the elliptic sector shares the form and properties with the well-known conformally flat condition approximation. We show the stability and convergence properties of the numerical scheme with numerical simulations of vacuum solutions. We have performed the first numerical evolutions of the coupled system of hydrodynamics and Einstein equations within FCF. As a proof of principle of the viability of the formalism, we present 2D axisymmetric simulations of an oscillating neutron star. In order to simplify the analysis we have neglected the backreaction of the gravitational waves into the dynamics, which is small ($<2\%$) for the system considered in this work. We use spherical coordinates grids which are well adapted for simulations of stars and allow for extended grids that marginally reach the wave zone. We have extracted the gravitational wave signature and compared it to the Newtonian quadrupole and hexadecapole formulas. Both extraction methods show agreement within the numerical errors and the approximations used ($\sim 30\%$).

We carry out a thorough analysis on a class of cosmological space-times which admit three spacelike Killing vectors of Bianchi class B and contain electromagnetic fields. Using dynamical system analysis, we show that a family of electro-vacuum plane-wave solutions of the Einstein-Maxwell equations is the stable attractor for expanding universes. Phase dynamics are investigated in detail for particular symmetric models. We integrate the system exactly for some special cases to confirm the qualitative features. Some of the obtained solutions have not been presented previously to the best of our knowledge. Finally, based on those analyses, we discuss the relation between those homogeneous models and perturbations of open Friedmann-Lemaitre-Robertson-Walker universes. We argue that the electro-vacuum plane-wave modes correspond to a certain long-wavelength limit of electromagnetic perturbations.

We perform a detailed examination of current constraints on annihilating and decaying dark matter models from both prompt and inverse-Compton emission photons, including both model-dependent and model-independent bounds. We also show that the observed isotropic diffuse gamma-ray background (DGRB), which provides one of the most conservative constraints on models of annihilating weak-scale dark matter particles, may enhance its sensitivity by a factor of $\sim 2$ to 3 (95% C.L.) as the Fermi-LAT experiment resolves DGRB contributing blazar sources with five years of observation. For our forecasts, we employ the results of constraints to the luminosity-dependent density evolution plus blazar spectral energy distribution sequence model, which is constrained by the DGRB and blazar source count distribution function.