Previously we showed that, based only on charge conjugation and isospin invariance of strong interactions, the difference cross sections of hadrons with opposite charge in semi-inclusive deep inelastic scattering (SIDIS) $e+N\to l+h+X$ are expressed solely in terms of the valence-quark densities and certain nonsinglet combinations of fragmentation functions (FFs). This allowed us to determine these quantities in a model-independent way. Now we extend this approach to processes when the transverse momentum of the final hadron is measured as well. We show that the difference cross sections of unpolarized SIDIS on proton and deuterium targets, $d{\sigma }_N^{h^{+}-h^{-}}$, $d{\sigma }_N^{{\pi }^{+}-{\pi }^{-}}$ and $d{\sigma }_N^{K^{+}-K^{-}}$, are expressed solely in terms of the transverse momentum-dependent (TMD) unpolarized valence-quark densities and FFs, and the valence-quark Boer-Mulders and Collins functions. This allows us to determine them separately and study the flavor dependence of the quark transverse momentum. Measurements on the deuterium target, $d{\sigma }_d^{h^{+}-h^{-}}$, $d{\sigma }_d^{{\pi }^{+}-{\pi }^{-}}$ and $d{\sigma }_d^{K^{+}-K^{-}}$, provide three independent measurements for the sum of the TMD valence-quark densities and Boer-Mulders functions: $(u_{1,V}+d_{1,V})$ and $(h_{1,uV}^{\perp }+h_{1,dV}^{\perp })$.

We present next-to-leading-order QCD predictions for cross sections and for a comprehensive set of distributions in $\gamma \gamma +2\text{−}\mathrm{jet}$ production at the Large Hadron Collider. We consider the contributions from loop amplitudes for two photons and four gluons, but we neglect top quarks. We use BlackHat together with SHERPA to carry out the computation. We use a Frixione cone isolation for the photons. We study standard sets of cuts on the jets and the photons and also sets of cuts appropriate for studying backgrounds to Higgs-boson production via vector-boson fusion.

We consider all the dimension-six operators as well as some simple extensions of the standard model that give new contributions to neutrino interactions with matter. Such interactions are usually parametrized by ${\epsilon }_{\alpha \beta }$, where $\alpha$ and $\beta$ are neutrino flavor indices taking the values $e$, $\mu$, and $\tau$. In the simple models we consider the ${\epsilon }_{\alpha \beta }$’s are much more constrained than in the operator-based model-independent approach. Typically the ${\epsilon }_{\alpha \beta }$’s are restricted to be smaller in magnitude than around ${10}^{-3}$. In some of the leptoquark models, a specific pattern for the leptoquark Yukawa couplings allows the diagonal element ${\epsilon }_{\tau \tau }$ to be as large as $\sim 0.1$, or one of ${\epsilon }_{ee}$, ${\epsilon }_{\mu \mu }\sim 0.01$. We discuss the interplay between neutrino physics and leptoquark searches at the LHC.

Results from a search for supersymmetry in events with four or more leptons including electrons, muons and taus are presented. The analysis uses a data sample corresponding to $20.3{\mathrm{fb}}^{-1}$ of proton-proton collisions delivered by the Large Hadron Collider at $\sqrt{s}=8\mathrm{TeV}$ and recorded by the ATLAS detector. Signal regions are designed to target supersymmetric scenarios that can be either enriched in or depleted of events involving the production of a $Z$ boson. No significant deviations are observed in data from standard model predictions and results are used to set upper limits on the event yields from processes beyond the standard model. Exclusion limits at the 95% confidence level on the masses of relevant supersymmetric particles are obtained. In $R$-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 and 750 GeV are placed on gluino and chargino masses, respectively. In $R$-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios.

The probability of spin flip of an electron due to a torsional wave is calculated. It is compared to the electromagnetic case, and ways to detect torsion are discussed.

We calculate the coefficients of the leading nonglobal logarithms for the hemisphere mass distribution analytically at 3, 4, and 5 loops at large $N_c$. We confirm that the integrand derived with the strong-energy-ordering approximation and fixed-order iteration of the Banfi-Marchesini-Syme (BMS) equation agree. Our calculation exploits a hidden $\mathrm{PSL}(2,\mathbb{R})$ symmetry associated with the jet directions, apparent in the BMS equation after a stereographic projection to the Poincaré disk. The required integrals have an iterated form, leading to functions of uniform transcendentality. This allows us to extract the coefficients, and some functional dependence on the jet directions, by computing the symbols and coproducts of appropriate expressions involving classical and Goncharov polylogarithms. Convergence of the series to a numerical solution of the BMS equation is also discussed.

Asymptotic single-particle states in quantum field theories with small departures from Lorentz symmetry are investigated perturbatively with focus on potential phenomenological ramifications. To this end, one-loop radiative corrections for a sample Lorentz-violating Lagrangian contained in the Standard-Model Extension are studied at linear order in Lorentz breakdown. It is found that the spinor kinetic operator, and thus the free-particle physics, is modified by Lorentz-violating operators absent from the original Lagrangian. As a consequence of this result, both the standard renormalization procedure as well as the Lehmann-Symanzik-Zimmermann reduction formalism need to be adapted. The necessary adaptations are worked out explicitly at first order in Lorentz-breaking coefficients.

We study Yang Mills theory in $2+1$ dimensions, as an array of coupled ($1+1$)-dimensional principal chiral sigma models. This can be understood as an anisotropic limit where one of the space-time dimensions is discrete and the others are continuous. The $SU(N)\times SU(N)$ principal chiral sigma model in $1+1$ dimensions is integrable, asymptotically free and has massive excitations. New exact form factors and correlation functions of the sigma model have recently been found by the author and P. Orland. In this paper, we use these new results to calculate physical quantities in ($2+1$)-dimensional Yang-Mills theory, generalizing previous $SU(2)$ results by Orland, which include the string tensions and the low-lying glueball spectrum. We also present a new approach to calculate two-point correlation functions of operators using the light glueball states. The anisotropy of the theory yields different correlation functions for operators separated in the $x^1$ and $x^2$ directions.

Several recent developments point to the fact that rational maps from $n$-punctured spheres to the null cone of $D$-dimensional momentum space provide a natural language for describing the scattering of massless particles in $D$ dimensions. In this paper we identify and study equations relating the kinematic invariants $s_{ab}$ and the puncture locations ${\sigma }_c$, which we call the scattering equations. We provide an inductive algorithm in the number of particles for their solutions and prove a remarkable property which we call Kawai–Lewellen–Tye (KLT) orthogonality. In a nutshell, KLT orthogonality means that “Parke–Taylor” vectors constructed from the solutions to the scattering equations are mutually orthogonal with respect to the KLT bilinear form. We end with comments on possible connections to gauge theory and gravity amplitudes in any dimension and to the high-energy limit of string theory amplitudes.

We develop a method to compute low-eccentricity initial data of binary neutron stars required to perform realistic simulations in numerical relativity. The orbital eccentricity is controlled by adjusting the orbital angular velocity of a binary and incorporating an approaching relative velocity of the neutron stars. These modifications improve the solution primarily through the hydrostatic equilibrium equation for the binary initial data. The orbital angular velocity and approaching velocity of initial data are updated iteratively by performing time evolutions over $\sim 3$ orbits. We find that the eccentricity can be reduced by an order of magnitude compared to standard quasicircular initial data, specifically from $\sim 0.01$ to $\lesssim 0.001$, by three successive iterations for equal-mass binaries leaving $\sim 10$ orbits before the merger.

Galileon interactions represent a class of effective field theories that have received much attention since their inception. They can be treated in their own right as scalar field theories with a specific global shift and Galilean symmetry or as a descendant of a more fundamental theory like massive gravity. It is well known that the Galileon theories are stable under quantum corrections thanks to the nonrenormalization theorem which is not due to the symmetry. We consider different covariant couplings of this Galileon scalar field with the matter field: the conformal coupling, the disformal coupling and the longitudinal coupling. We compute the one-loop quantum corrections to the Galileon interactions from the coupling to the external matter fields. In all the considered cases of covariant couplings we show that the terms generated by one-loop matter corrections not only renormalize the Galileon interactions but also give rise to higher order derivative ghost interactions. However, the renormalized version of the Galileon interactions as well as the new interactions come at a scale suppressed by the original classical coupling scale and hence are harmless within the regime of the effective field theory.

Massive scalar test fields around Kerr black holes can form quasibound states with complex frequencies. Some of these states decay in time, but some others—in the superradiant regime—grow, causing a superradiant instability. Precisely at the threshold between decaying and growing modes, there exist bound states with real frequency, known as scalar clouds. Fully nonlinear counterparts of these clouds have been shown to yield Kerr black holes with scalar hair. Here, we consider massive, (electrically) charged, test scalar, and Proca fields on the background of Reissner-Nordström black holes. By computing the quasibound state frequencies, we establish that no such states exist in the superradiant regime for the Proca field—a similar behavior to that known for scalar fields. But decaying quasibound states with an arbitrarily small imaginary part of the frequency exist and thus are arbitrarily long lived. In the limit of a vanishing imaginary part of the frequency, the field does not trivialize, and we dub the corresponding configurations as marginal (charged) scalar or Proca clouds, since they are only marginally bound. We comment on the possible existence of nonlinear counterparts to these marginal clouds.

We present novel methods to numerically address the problem of characterizing the response of particle detectors in curved spacetimes. These methods allow for the integration of the Wightman function, at least in principle, in rather general backgrounds. In particular we will use this tool to further understand the nature of conformal massless scalar Hawking radiation from a Schwarzschild black hole in anti–de Sitter space. We do that by studying an Unruh-DeWitt detector at rest above the horizon and in circular-geodesic orbit. The method allows us to see that the response rate shows peaks at certain characteristic frequencies, which correspond to the quasinormal modes of the spacetime. It is in principle possible to apply these techniques to more complicated and interesting physical scenarios, e.g., geodesic infall or multiple detector entanglement evolution, or the study of the behavior of quantum correlations in spacetimes with black hole horizons.

The spins of a number of supermassive and stellar-mass black holes have been measured based on detections of thermal continuum emission and relativistically broadened iron lines in their x-ray spectra. Likewise, quasiperiodic variability has been observed in several sources. Such measurements commonly make the assumption that black holes are described by the Kerr metric, which according to the no-hair theorem characterizes black holes uniquely in terms of their masses and spins. This fundamental property of black holes can be tested observationally by measuring potential deviations from the Kerr metric introduced by a parametrically deformed Kerr-like spacetime. Thermal spectra, iron lines, and variability have already been studied extensively in several such metrics, which usually depend on only one particular type of deviation or contain unphysical regions outside of the compact object. In this paper, I study these x-ray probes in the background of a new Kerr-like metric which depends on four independent deviation functions and is free of pathological regions outside of the event horizon. I show that the observed signals depend significantly on primarily two types of deviations and that the strong correlation between the spin and the deviation parameters found previously in other Kerr-like metrics is partially broken for rapidly spinning black holes. This suggests that high-spin sources are the best candidates for tests of the no-hair theorem with x rays and I obtain first constraints on such deviations from the stellar-mass black hole Cygnus X-1.

We demonstrate that for a cosmic variance limited experiment, cosmic microwave background (CMB) $E$ polarization alone places stronger constraints on cosmological parameters than CMB temperature. For example, we show that $C_{\ell }^{\mathrm{EE}}$ can constrain parameters better than $C_{\ell }^{\mathrm{TT}}$ by up to a factor 2.8 when a multipole range of $\ell =30–2500$ is considered. We expose the physical effects at play behind this remarkable result and study how it depends on the multipole range included in the analysis. In most relevant cases, $C_{\ell }^{\mathrm{TE}}$ or $C_{\ell }^{\mathrm{EE}}$ surpass the $C_{\ell }^{\mathrm{TT}}$-based cosmological constraints. This result is important as the small-scale astrophysical foregrounds are expected to have a much reduced impact on polarization, thus opening the possibility of building cleaner and more stringent constraints of the $\mathrm{\Lambda }\mathrm{CDM}$ model. This is relevant especially for proposed future CMB satellite missions, such as CORE or PRISM, that are designed to be cosmic variance limited in polarization till very large multipoles. We perform the same analysis for a Planck-like experiment, and conclude that even in this case $C_{\ell }^{\mathrm{TE}}$ alone should determine the constraint on ${\mathrm{\Omega }}_c{h}^2$ better than $C_{\ell }^{\mathrm{TT}}$ by $\sim 15\%$, while determining ${\mathrm{\Omega }}_b{h}^2$, $n_s$ and $\theta$ with comparable accuracy. Finally, we explore a few classical extensions of the $\mathrm{\Lambda }\mathrm{CDM}$ model and show again that CMB polarization alone provides more stringent constraints than CMB temperature in the case of a cosmic variance limited experiment.

The uniform asymptotic approximation method provides a powerful, systematically improved, and error-controlled approach to construct accurate analytical approximate solutions of mode functions of perturbations of the Friedmann-Robertson-Walker universe, designed especially for the cases where the relativistic linear dispersion relation is modified after gravitational quantum effects are taken into account. These include models from string/M Theory, loop quantum cosmology and Hořava-Lifshitz quantum gravity. In this paper, we extend our previous studies of the first-order approximations to high orders for the cases where the modified dispersion relation (linear or nonlinear) has only one turning point (or zero). We obtain the general expressions for the power spectra and spectral indices of both scalar and tensor perturbations up to the third order, at which the error bounds are $\lesssim 0.15\%$. As an application of these formulas, we calculate the power spectra and spectral indices in the slow-roll inflation with a nonlinear power-law dispersion relation. To check the consistency of our formulas, we further restrict ourselves to the relativistic case, and calculate the corresponding power spectra, spectral indices and runnings to the second order. Then, we compare our results with the ones obtained by the Green function method and show explicitly that the results obtained by these two different methods are consistent within the allowed errors.

We present the first measurement of the cross correlation of weak gravitational lensing and the extragalactic $\gamma$-ray background emission using data from the Canada-France-Hawaii Lensing Survey and the Fermi Large Area Telescope. The cross correlation is a powerful probe of signatures of dark matter annihilation, because both cosmic shear and gamma-ray emission originate directly from the same dark matter distribution in the Universe, and it can be used to derive constraints on the dark matter annihilation cross section. We show that the measured lensing-$\gamma$ correlation is consistent with a null signal. Comparing the result to theoretical predictions, we exclude dark matter annihilation cross sections of $⟨\sigma v⟩={10}^{-24}–{10}^{-25}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for a 100 GeV dark matter. If dark matter halos exist down to the mass scale of ${10}^{-6}{M}_{\odot }$, we are able to place constraints on the thermal cross sections $⟨\sigma v⟩\sim 5\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for a 10 GeV dark matter annihilation into ${\tau }^{+}{\tau }^{-}$. Future gravitational lensing surveys will increase sensitivity to probe annihilation cross sections of $⟨\sigma v⟩\sim 3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ even for a 100 GeV dark matter. Detailed modeling of the contributions from astrophysical sources to the cross correlation signal could further improve the constraints by $\sim 40\%–70\%$.

We present a class of supersymmetric models in which symmetry considerations alone dictate the form of the soft SUSY breaking Lagrangian. We develop a class of minimal models, denoted as sMSSM—for flavor symmetry-based minimal supersymmetric standard model—that respect a grand unified symmetry such as $SO(10)$ and a non-Abelian flavor symmetry $H$ which suppresses SUSY-induced flavor violation. Explicit examples are constructed with the flavor symmetry being gauged $SU(2{)}_H$ and $SO(3{)}_H$ with the three families transforming as $\mathbf{2}+\mathbf{1}$ and $\mathbf{3}$ representations, respectively. A simple solution is found in the case of $SU(2{)}_H$ for suppressing the flavor violating $D$–terms based on an exchange symmetry. Explicit models based on $SO(3{)}_H$ without the $D$–term problem are developed. In addition, models based on discrete non-Abelian flavor groups are presented which are automatically free from $D$–term issues. The permutation group $S_3$ with a $\mathbf{2}+\mathbf{1}$ family assignment, as well as the tetrahedral group $A_4$ with a $\mathbf{3}$ assignment are studied. In all cases, a simple solution to the SUSY $CP$ problem is found, based on spontaneous $CP$ violation leading to a complex quark mixing matrix. We develop the phenomenology of the resulting sMSSM, which is controlled by seven soft SUSY breaking parameters for both the $\mathbf{2}+\mathbf{1}$ assignment and the $\mathbf{3}$ assignment of fermion families. These models are special cases of the phenomenological MSSM (pMSSM), but with symmetry restrictions. We discuss the parameter space of sMSSM compatible with LHC searches, $B$-physics constraints and dark matter relic abundance. Fine-tuning in these models is relatively mild, since all SUSY particles can have masses below about 3 TeV.

Normalized hypercubic smearing improves the behavior of dynamical Wilson-clover fermions, but has the unwanted side effect that it can occasionally produce spikes in the fermion force. These spikes originate in the chain rule connecting the derivative with respect to the smeared links to the derivative with respect to the dynamical links, and are associated with the presence of dislocations in the dynamical gauge field. We propose and study an action designed to suppress these dislocations. We present evidence for improved performance of the hybrid Monte Carlo algorithm. A side benefit is improvement in the properties of valence chiral fermions.

We systematically study exclusiv2 diffractive (photo)production of vector mesons ($J/\psi$, $\psi (2s)$, $\varphi$, and $\rho$) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive $\psi (2s)$ and $\rho$ production at HERA and $J/\psi$ photoproduction with all available data, including recent work from HERA, ALICE, and LHCb, finding good agreement. In particular, we show that the $t$ distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and nonsaturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the $t$ distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible $|t|$ that can be traced back to the unitarity features of color dipole amplitude in the saturation regime. We show that in saturation models the dips in $t$ distribution recede towards lower $|t|$ with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-$x$, and decreasing virtuality $Q$. We provide various predictions for exclusive (photo)production of different vector mesons including the ratio of $\psi (2s)/J/\psi$ at HERA, the LHC, and future colliders.