Collider searches for energetic particles recoiling against missing transverse energy $({\cancel{E}}_T)$ allow us to place strong bounds on the interactions between dark matter (DM) and standard model (SM) particles. In this article we update and extend LHC constraints on effective dimension-7 operators involving DM and electroweak gauge bosons. A concise comparison of the sensitivity of the monophoton, mono-$W$, mono-$Z$, mono-$W/Z$, and invisible Higgs-boson decays in the vector boson fusion mode and the monojet channel is presented. Depending on the parameter choices, either the monophoton or the monojet data provide the most stringent bounds at the moment. We furthermore explore the potential of improving the current 8 TeV limits at 14 TeV. Future strategies capable of disentangling the effects of the different effective operators involving electroweak gauge bosons are discussed as well.

A search is performed for top-quark pairs ($t\overline{t}$) produced together with a photon ($\gamma$) with transverse energy greater than 20 GeV using a sample of $t\overline{t}$ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of $4.59{\mathrm{fb}}^{-1}$ of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 $t\overline{t}\gamma$ candidate events are observed in the electron and muon channels, to be compared to the expectation of $79\pm 26$ and $120\pm 39$ non-$t\overline{t}\gamma$ background events, respectively. The production of $t\overline{t}\gamma$ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The $t\overline{t}\gamma$ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is ${\sigma }_{t\overline{t}\gamma }^{\mathrm{fid}}\times \mathrm{BR}=63\pm 8{(\text{stat})}_{-13}^{+17}(\text{syst})\pm 1(\text{lumi})\mathrm{fb}$ per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of $48\pm 10\mathrm{fb}$.

We use the conformal bootstrap to study conformal field theories with $O(N)$ global symmetry in $d=5$ and $d=5.95$ space-time dimensions that have a scalar operator ${\varphi }_i$ transforming as an $O(N)$ vector. The crossing symmetry of the four-point function of this $O(N)$ vector operator, along with unitarity assumptions, determines constraints on the scaling dimensions of conformal primary operators in the ${\varphi }_i\times {\varphi }_j$ operator product expansionİmposing a lower bound on the second smallest scaling dimension of such an $O(N)$-singlet conformal primary, and varying the scaling dimension of the lowest one, we obtain an allowed region that exhibits a kink located very close to the interacting $O(N)$-symmetric conformal field theory conjectured to exist recently by Fei, Giombi, and Klebanov. Under reasonable assumptions on the dimension of the second lowest $O(N)$ singlet in the ${\varphi }_i\times {\varphi }_j$ operator product expansion, we observe that this kink disappears in $d=5$ for small enough $N$, suggesting that in this case an interacting $O(N)$ conformal field theory may cease to exist for $N$ below a certain critical value.

We investigate the effects of the anomalous magnetic moment (AMM) in the equation of state (EOS) of a system of charged fermions at finite density in the presence of a magnetic field. In the region of strong magnetic fields ($eB>m^2$), the AMM is found from the one-loop fermion self-energy. In contrast to the weak-field AMM found by Schwinger, in the strong magnetic field region the AMM depends on the Landau level and decreases with it. The effects of the AMM in the EOS of a dense medium are investigated at strong and weak fields using the appropriate AMM expression for each case. In contrast with what has been reported in other works, we find that the AMM of charged fermions makes no significant contribution to the EOS at any field value.

We study a Skyrme-type model with a quadratic potential for a field with $S^2$ vacua. We consider two flavors of the model, the first is the Skyrme model and the second has a sixth-order derivative term instead of the Skyrme term; both with the added quadratic potential. The model contains molecules of half Skyrmions, each of them is a global (anti)monopole with baryon number $1/2$. We numerically construct solutions with baryon numbers one through six, and find stable solutions which look like beads on rings. We also construct a molecule with fractional Skyrmions having the baryon numbers $1/3+2/3$, by adding a linear potential term.

A coset model based on the hyperbolic Kac-Moody algebra ${\mathrm{E}}_{10}$ has been conjectured to underlie 11-dimensional supergravity and M theory. In this note we study the canonical structure of the bosonic model for finite- and infinite-dimensional groups. In the case of finite-dimensional groups like $GL(n)$ we exhibit a convenient set of variables with Borel-type canonical brackets. The generalization to the Kac-Moody case requires a proper treatment of the imaginary roots that remains elusive. As a second result, we show that the supersymmetry constraint of $D=11$ supergravity can be rewritten in a suggestive way using ${\mathrm{E}}_{10}$ algebra data. Combined with the canonical structure, this rewriting explains the previously observed association of the canonical constraints with null roots of ${\mathrm{E}}_{10}$. We also exhibit a basic incompatibility between local supersymmetry and the $K({\mathrm{E}}_{10})$ “R symmetry” that can be traced back to the presence of imaginary roots and to the unfaithfulness of the spinor representations occurring in the present formulation of the ${\mathrm{E}}_{10}$ worldline model, and that may require a novel type of bosonization/fermionization for its resolution. This appears to be a key challenge for future progress with ${\mathrm{E}}_{10}$.

A thermal relic, often referred to as a weakly interacting massive particle (WIMP), is a particle produced during the early evolution of the Universe whose present (relic) abundance depends only on its mass and its thermally averaged annihilation cross section (annihilation rate factor) $⟨\sigma v{⟩}_{\text{ann}}$. Late time WIMP annihilation has the potential to affect the cosmic microwave background (CMB) power spectrum. Current observational constraints on the absence of such effects provide bounds on the mass and the annihilation cross section of relic particles that may be, but need not be, dark matter candidates. For a WIMP that is a dark matter candidate, the CMB constraint sets an upper bound to the annihilation cross section, leading to a lower bound to its mass that depends on whether or not the WIMP is its own antiparticle. For a self-conjugate WIMP, $m_{\min }=50f\mathrm{GeV}$, where $f\le 1$ is an electromagnetic energy efficiency factor. For a non–self-conjugate WIMP, the minimum mass is a factor of two larger. For a WIMP that is a subdominant component of the dark matter density there is no bound on its mass and the upper bound to its annihilation cross section imposed by the CMB transforms into a lower bound to its annihilation cross section. These results are outlined and quantified here using the latest CMB constraints for a stable, symmetric (equal number of particles and antiparticles), WIMP whose annihilation is s-wave dominated, and for particles that are, or are not, their own antiparticle.

The $\mathrm{\Lambda }\mathrm{CDM}$ framework offers a remarkably good description of our Universe with a very small number of free parameters, which can be determined with high accuracy from currently available data. However, this does not mean that the associated physical quantities, such as the curvature of the Universe, have been directly measured. Similarly, general relativity is assumed, but not tested. Testing the relevance of general relativity for cosmology at the background level includes a verification of the relation between its energy contents and the curvature of space. Using an extended Newtonian formulation, we propose an approach where this relation can be tested. Using the recent measurements on cosmic microwave background, baryonic acoustic oscillations and the supernova Hubble diagram, we show that the prediction of general relativity is well verified in the framework of standard $\mathrm{\Lambda }\mathrm{CDM}$ assumptions, i.e. an energy content only composed of matter and dark energy, in the form of a cosmological constant or equivalently a vacuum contribution. However, the actual equation of state of dark fluids cannot be directly obtained from cosmological observations. We find that relaxing the equation of state of dark energy opens a large region of possibilities, revealing a new type of degeneracy between the curvature and the total energy content of the Universe.

We explore thick accretion disks around rotating attractors. We detail the configurations analyzing the fluid angular momentum and finally provide a characterization of the disk morphology and different possible topologies. Investigating the properties of orbiting disks, a classification of attractors, possibly identifiable in terms of their spin-mass ratio, is introduced; then an attempt to characterize dynamically a series of different disk topologies is discussed, showing that some of the toroidal configuration features are determined by the ratio of the angular momentum of the orbiting matter and the spin-mass ratio of the attractor. Then we focus on “multistructured” disks constituted by two or more rings of matter orbiting the same attractor, and we prove that some structures are constrained in the dimension of rings, spacing, location, and an upper limit of ring number is provided. Finally, assuming a polytropic equation of state, we study some specific cases.

The single integral form of the Pasquier inversion representation of the Khuri–Treiman equation presents great advantages for describing the final-state interaction of three-body decay or production processes. However, the original form of the Pasquier inversion representation is only given in the decay region and regions below. For the regions above, analytic continuation of original form is required. Because of the nontrivial nature of the analytic continuation procedure, it is the purpose of this work to obtain a well-defined Pasquier inversion representation of the Khuri–Treiman equation for the entire energy range.

The Bethe-Salpeter equation in the diquark channel is investigated by employing the Dyson-Schwinger method together with the Munczek-Nemirovsky model. The novelty of our study is a resummation of completely crossed ladder diagrams in the Bethe-Salpeter kernel. These diagrams are enhanced due to their color factors in the diquark channel, but not in the meson channel. In our analysis, diquark bound-state solutions exist in the Bethe-Salpeter equation.

The transition form factor for electrodisintegration of a two-body bound system is calculated in the Bethe–Salpeter framework. For the initial (bound) and the final (scattering) states, we use our solutions of the Bethe–Salpeter equation in Minkowski space which were first obtained recently. The gauge invariance, which manifests itself in the conservation of the transition electromagnetic current $J·q=0$, is studied numerically. It results from a cancellation between the plane wave and the final state interaction contributions. This cancellation takes place only if the initial bound state Bethe–Salpeter amplitude, the final scattering state, and the operator of electromagnetic current are strictly consistent with each other, that is if they are found in the same dynamical framework. A reliable result for the transition form factor can be obtained in this case only.

The holographic soft-wall model is successful in the phenomenology of hadrons. Here, with the use of generalized parton distributions (GPDs) obtained from AdS/QCD, perturbative effects are entered into the formalism. Perturbations are incorporated in the formalism through the evolution of GPDs according to the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi-like (DGLAP) equations. Evolved proton GPDs are compared with a phenomenological model to show that we can get good improvements of the holographic model. In this paper we show that combining the holographic soft-wall model and perturbative effects, can give the correct physics of phenomenological GPDs.

We show that a neutral scalar field, $\sigma$, of two-Higgs-doublet extensions of the Standard Model incorporating the seesaw mechanism for neutrino masses can be identified as a consistent warm dark matter candidate with a mass of order keV. The relic density of $\sigma$ is correctly reproduced by virtue of the late decay of a right-handed neutrino $N$ participating in the seesaw mechanism. Constraints from cosmology determine the mass and lifetime of $N$ to be $M_N\approx 25\mathrm{GeV}–20\mathrm{TeV}$ and ${\tau }_N\approx (10^{-4}-1)\sec$. These models can also explain the 3.5 keV X-ray anomaly in the extragalactic spectrum that has been recently reported in terms of the decay $\sigma \to \gamma \gamma$. Future tests of these models at colliders and in astrophysical settings are outlined.

If the electroweak symmetry breaking sector turns out to be strongly interacting, the actively investigated effective theory for longitudinal gauge bosons plus Higgs can be efficiently extended to cover the regime of saturation of unitarity (where the perturbative expansion breaks down). This is achieved by dispersion relations, whose subtraction constants and left cut contribution can be approximately obtained in different ways, giving rise to different unitarization procedures. We illustrate the ideas with the inverse amplitude method, one version of the N/D method, and another improved version of the $K$ matrix. In the three cases we get partial waves which are unitary, analytical with the proper left and right cuts, and in some cases poles in the second Riemann sheet that can be understood as dynamically generated resonances. In addition, they reproduce at next to leading order the perturbative expansion for the five partial waves not vanishing (up to $J=2$), and they are renormalization scale ($\mu$) independent. Also the unitarization formalisms are extended to the coupled channel case. Then we apply the results to the elastic scattering amplitude for the longitudinal components of the gauge bosons $V=W,Z$ at high energy. We also compute $hh\to hh$ and the inelastic process $VV\to hh$ which are coupled to the elastic $VV$ channel for custodial isospin $I=0$. We numerically compare the three methods for various values of the low-energy couplings and explain the reasons for the differences found in the $I=J=1$ partial wave. Then we study the resonances appearing in the different elastic and coupled channels in terms of the effective Lagrangian parameters.

Evolution of quark-gluon plasma near equilibrium can be described by the second-order relativistic viscous hydrodynamic equations. Consistent and analytically verifiable numerical solutions are critical for phenomenological studies of the collective behavior of quark-gluon plasma in high-energy heavy-ion collisions. A novel analytical solution based on the conformal Gubser flow that is a boost-invariant solution with transverse fluid velocity is presented. Because of the nonlinear nature of the equation, the analytical solution is nonperturbative and exhibits features that are rather distinct from solutions to usual linear hydrodynamic equations. It is used to verify with high precision the numerical solution with a newly developed state-of-the-art $(3+1)$-dimensional second-order viscous hydro code (CLVisc). The perfect agreement between the analytical and numerical solutions demonstrates the reliability of the numerical simulations with the second-order viscous corrections. This lays the foundation for future phenomenological studies that allow one to gain access to the second-order transport coefficients.

We measure the forward-backward asymmetry in the production of ${\mathrm{\Lambda }}_b^0$ and ${\overline{\mathrm{\Lambda }}}_b^0$ baryons as a function of rapidity in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using $10.4{\mathrm{fb}}^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. The asymmetry is determined by the preference of ${\mathrm{\Lambda }}_b^0$ or ${\overline{\mathrm{\Lambda }}}_b^0$ particles to be produced in the direction of the beam protons or antiprotons, respectively. The measured asymmetry integrated over rapidity $y$ in the range $0.1<|y|<2.0$ is $A=0.04\pm 0.07(\text{stat})\pm 0.02(\text{syst})$.

Within the Dirac model for the electronic excitations of graphene, we calculate the full polarization tensor with finite mass and chemical potential. It has, besides the (00)-component, a second form factor, which must be accounted for. We obtain explicit formulas for both form factors and for the reflection coefficients. Using these, we discuss the regions in the momentum-frequency plane where plasmons may exist and give numeric solutions for the plasmon dispersion relations. It turns out that plasmons exist for both, transverse electric and transverse magnetic polarizations over the whole range of the ratio of mass to chemical potential, except for zero chemical potential, where only a TE plasmon exists.

We analyze the critical exponents relating to the quark mass anomalous dimension and $\beta$-function at the Banks-Zaks fixed point in quantum chromodynamics in a variety of representations for the quark in the momentum subtraction schemes of Celmaster and Gonsalves. For a specific range of values of the number of quark flavors, estimates of the exponents appear to be scheme independent. Using the recent five-loop modified minimal subtraction scheme, quark mass anomalous dimension, and estimates of the fixed point location, we estimate the associated exponent as 0.263–0.268 for the $SU(3)$ color group and 12 flavors when the quarks are in the fundamental representation.