We present a new strategy to uncover light, quasidegenerate Higgsinos, a likely ingredient in a natural supersymmetric model. Our strategy focuses on Higgsinos with interstate splittings of $O(5-50)\mathrm{GeV}$ that are produced in association with a hard, initial-state jet and decay via off-shell gauge bosons to two or more leptons and missing energy, $pp\to j+{\cancel{E}}_T+2^{+}\ell$. The additional jet is used for triggering, allowing us to significantly loosen the lepton requirements and gain sensitivity to small inter-Higgsino splittings. Focusing on the two-lepton signal, we find the seemingly large backgrounds from diboson plus jet, $\overline{t}t$ and $Z/{\gamma }^{*}+j$ can be reduced with careful cuts, and that fake backgrounds appear minor. For Higgsino masses $m_{\chi }$ just above the current LEP II bound ($\mu \simeq 110\mathrm{GeV}$) we find the significance can be as high as $3\sigma$ at the LHC using the existing $20{\mathrm{fb}}^{-1}$ of 8 TeV data. Extrapolating to LHC at 14 TeV with $100{\mathrm{fb}}^{-1}$ of data, and as one example $M_1=M_2=500\mathrm{GeV}$, we find $5\sigma$ evidence for $m_{\chi }\lesssim 140\mathrm{GeV}$ and $2\sigma$ evidence for $m_{\chi }\lesssim 200\mathrm{GeV}$. We also present a reinterpretation of ATLAS/CMS monojet bounds in terms of degenerate Higgsino ($\delta m_{\chi }\ll 5\mathrm{GeV}$) plus jet production. We find the current monojet bounds on $m_{\chi }$ are no better than the chargino bounds from LEP II.

Employing scalar QCD we study the gluon emission of heavy quarks created by the interaction with light quarks considered as dynamical scattering centers. We develop approximation formulas for the high-energy limit and study when the full calculation reaches this high-energy limit. For zero quark masses and in the high-energy limit our model reproduces the Gunion-Bertsch results. We justify why scalar QCD represents a good approximation to the full QCD approach for the energy loss of heavy quarks. In the regime of accessible phenomenology we observe that the emission at small transverse momentum (dead cone effect) is less suppressed than originally suggested. We also investigate the influence of a finite gluon mass on the discussed results.

We calculate the scalar, axial, and pseudoscalar charges of the quark in the Schwinger-Dyson formalism of Landau gauge QCD. It is found that the dressed quark-scalar density of the valence quark is significantly enhanced against the bare-quark contribution, and the result explains qualitatively the phenomenologically known value of the pion-nucleon sigma term and also that given by lattice QCD. Moreover, we show that the Richardson’s interquark potential suppresses the quark-scalar density in the Higashjima-Miransky approximation. This fact suggests that the quark-scalar density is an observable that is sensitive to quark confinement. For the quark axial charge, we find that it is suppressed due to the gluon dynamics. The result of the quenched analysis agrees qualitatively with the experimental data of the isovector axial coupling constant $g_A$. We show that the suppression of the quenched axial charge is due to a mechanism similar to that of the quark tensor charge. In the Schwinger-Dyson equation with the leading unquenching quark-loop contribution the quark axial charge is more suppressed, due to the anomaly effect. The quark pseudoscalar density is found to be large, and is divergent as the bare quark becomes massless. This result is in agreement with the phenomenological current algebraic analysis, and explains well the dominance of the pion-pole contribution.

Sterile neutrinos with masses in the range of 1–100 GeV have been searched for in a variety of experiments. Here, we discuss the prospects of searching for sterile neutrinos at the LHC using displaced vertices. Two different cases are discussed: (i) the standard model extended with sterile neutrinos, and (ii) right-handed neutrinos in a left-right symmetric extension of the standard model. A dedicated displaced vertex search will allow us to probe parts of the parameter space not accessible to other searches, but both cases will require a large luminosity.

Temperature dependence of pion and sigma-meson screening masses is evaluated by the Polyakov-loop extended Nambu–Jona-Lasinio (PNJL) model with the entanglement vertex. We propose a practical way of calculating meson screening masses in the NJL-type effective models. The method based on the Pauli-Villars regularization solves the well-known difficulty that the evaluation of screening masses is not easy in the NJL-type effective models. The PNJL model with the entanglement vertex and the Pauli-Villars regularization well reproduces lattice QCD results on temperature dependence of the chiral condensate and the Polyakov loop. The method is applied to analyze temperature dependence of pion screening masses calculated with state-of-the-art lattice simulations with success in reproducing the lattice QCD results.

The leitmotif of this paper is the question of whether four- and higher even-dimensional conformal gravities do have a Chern-Simons pedigree. We show that Weyl gravity can be obtained as the dimensional reduction of a five-dimensional Chern-Simons action for a suitable (gauge-fixed, tractorlike) five-dimensional anti–de Sitter connection. The gauge-fixing and dimensional reduction program readily admits a generalization to higher dimensions for the case of certain conformal gravities obtained by contractions of the Weyl tensor.

We show the existence of physical superluminal modes and acausality in the Brans-Dicke type of extension of teleparallel gravity that includes $F(T)$ gravity and teleparallel dark energy as special cases. We derive the characteristic hypersurface for the extra degrees of freedom in the theory, thereby showing that the time evolution is not unique and closed causal curves can appear. Furthermore, we present a concrete disastrous solution in Bianchi type I spacetime, in which the anisotropy in expansion can be any function of time, and thus anisotropy can emerge suddenly, a simple demonstration that the theory is physically problematic.

Kastor–Traschen-type solution in a cosmological setup is studied in this article. We examine a hybrid of a Kastor–Traschen metric and a Friedmann–Robertson–Walker–Lemaitre solution. The problem is treated in a general number of dimensions $D\ge 4$, and we include the cosmological constant $\mathrm{\Lambda }$ parameter into the Einstein–Maxwell equations. The matter source consists of two fluids—charged dust and neutral fluid with nonvanishing pressure. The equations of motion for the fluid and electromagnetic field are written down, and an exact solution generalizing the extremely charged Reissner–Nordström black hole to an arbitrary spatial curvature parameter is presented. We examine metric and singularities of curvature scalars, trapped horizons, and energy conditions.

In the context of scalar tensor theories for gravity, there is a universally adopted hypothesis when running $N$-body simulations that time derivatives in the equation of motion for the scalar field are negligible. In this work we propose to test this assumption for one specific scalar-tensor model with a gravity screening mechanism: the symmetron. To this end, we implemented the necessary modifications to include the nonstatic terms in the $N$-body code Ramses. We present test cases and results from cosmological simulations. Our main finding when comparing static vs nonstatic simulations is that the global power spectrum is only slightly modified when taking into account the inclusion of nonstatic terms. On the contrary, we find that the calculation of the local power spectrum gives different measurements. Such results imply one must be careful when assuming the quasistatic approximation when investigating the environmental effects of modified gravity and screening mechanisms in structure formation of halos and voids distributions.

In this paper, we first propose a universal coupling between the gravity and matter in the framework of the Hořava-Lifshitz (HL) theory of gravity with an extra U(1) symmetry for both the projectable and nonprojectable cases. Then, using this universal coupling we study the post-Newtonian approximations and obtain the parametrized post-Newtonian (PPN) parameters in terms of the coupling constants of the theory. Contrary to the previous works in which only two PPN parameters were calculated, we obtain all PPN parameters. We then, for the first time in either projectable or nonprojectable cases, find that all the solar system tests carried out so far are satisfied in a large region of the parameter space. In particular, the same results obtained in general relativity can be easily realized here. A remarkable feature is that the solar system tests impose no constraint on the parameter $\lambda$ appearing in the kinetic part of the action. As a result, the solar system tests, when combined with the condition for avoidance of strong coupling, do not lead to an upper bound on the energy scale $M_{*}$ that suppresses higher-dimensional operators in the theory. This is in sharp contrast to other versions of the HL theory.

A compact object moving in curved spacetime interacts with its own gravitational field. This leads to both dissipative and conservative corrections to the motion, which can be interpreted as a self-force acting on the object. The original formalism describing this self-force relied heavily on the Green function of the linear differential operator that governs gravitational perturbations. However, because the global calculation of Green functions in nontrivial black-hole spacetimes has been an open problem until recently, alternative methods were established to calculate self-force effects using sophisticated regularization techniques that avoid the computation of the global Green function. We present a method for calculating the self-force that employs the global Green function and is therefore closely modeled after the original self-force expressions. Our quantitative method involves two stages: (i) numerical approximation of the retarded Green function in the background spacetime; (ii) evaluation of convolution integrals along the worldline of the object. This novel approach can be used along arbitrary worldlines, including those currently inaccessible to more established computational techniques. Furthermore, it yields geometrical insight into the contributions to self-interaction from curved geometry (backscattering) and trapping of null geodesics. We demonstrate the method on the motion of a scalar charge in Schwarzschild spacetime. This toy model retains the physical history dependence of the self-force but avoids gauge issues and allows us to focus on basic principles. We compute the self-field and self-force for many worldlines including accelerated circular orbits, eccentric orbits at the separatrix, and radial infall. This method, closely modeled after the original formalism, provides a promising complementary approach to the self-force problem.

We determine the full $C_{\ell }$ spectra and correlation functions of the temperature and polarization anisotropies in the cosmic microwave background (CMB), generated by a source modeled by the large-$N$ limit of spontaneously broken global $O(N)$-theories. We point out a problem in the standard approach of treating the radiation-matter transition by interpolating the eigenvectors of the unequal-time correlators of the source energy-momentum tensor. This affects the CMB predictions from all types of cosmic defects. We propose a method to overcome this difficulty. We find that in the large-$N$ global model that we study, differences in the final CMB power spectra amplitudes reach $\sim 10\%–20\%$ in all channels (TT, EE, BB and TE) when compared to implementations of the eigenvector interpolation technique. We also discuss how to optimally search for the contribution in the CMB from active sources such as cosmic defects in experiments like Planck, COrE and PRISM.

Very recently the IceCube Collaboration has reported an observation of 28 neutrino candidates with energies between 50 TeV and 2 PeV, constituting a $4.1\sigma$ excess compared to the atmospheric background. In this article we investigate the compatibility between the data and a hypothesized unbroken power-law neutrino spectrum for various values of spectral index $\mathrm{\Gamma }\ge 2$. We show that $\mathrm{\Gamma }\sim 2.3$ is consistent at the $\sim 1.5\sigma$ level with the observed events up to 2 PeV and to the null observation of events at higher energies. We then assume that the sources of this unbroken spectrum are Galactic, and deduce (i) an energy-transfer fraction from parent protons to pions (finding ${\epsilon }_{{\pi }^{\pm }}$ and ${\epsilon }_{\pi }$), and (ii) a way of discriminating among models which have been put forth to explain the “knee” and “ankle” features of the cosmic ray spectrum. Future IceCube data will test the unbroken power-law hypothesis and provide a multimessenger approach to explaining features of the cosmic ray spectrum, including the transition from Galactic to extragalactic dominance.

The direct detection of gravitational waves with upcoming second-generation gravitational wave observatories such as Advanced LIGO and Advanced Virgo will allow us to probe the genuinely strong-field dynamics of general relativity (GR) for the first time. We have developed a data analysis pipeline called TIGER (test infrastructure for general relativity), which uses signals from compact binary coalescences to perform a model-independent test of GR. In this paper we focus on signals from coalescing binary neutron stars, for which sufficiently accurate waveform models are already available which can be generated fast enough on a computer that they can be used in Bayesian inference. By performing numerical experiments in stationary, Gaussian noise, we show that for such systems, TIGER is robust against a number of unmodeled fundamental, astrophysical, and instrumental effects, such as differences between waveform approximants, a limited number of post-Newtonian phase contributions being known, the effects of neutron star tidal deformability on the orbital motion, neutron star spins, and instrumental calibration errors.

We have calculated the potentials of the heavy (charmed or bottomed) pseudoscalar mesons up to $O({\epsilon }^2)$ with the heavy meson chiral perturbation theory. We take into account the contributions from the football, triangle, box, and crossed diagrams with the $2\varphi$ exchange and one-loop corrections to the contact terms. We notice that the total $2\varphi$-exchange potential alone is attractive in the small momentum region in the channel ${\overline{B}\overline{B}}^{I=1}$, ${{\overline{B}}_s{\overline{B}}_s}^{I=0}$, or ${\overline{B}{\overline{B}}_s}^{I=1/2}$, while repulsive in the channel ${\overline{B}\overline{B}}^{I=0}$. Hopefully the analytical chiral structures of the potentials may be useful in the extrapolation of the heavy meson interaction from lattice QCD simulation.

Sufficient control of transition form factors is a vital ingredient for the precision flavor programs including the nearer term searches at the Large Hadron Collider and the forthcoming Belle II experiment. We improve on existing methods to extract $B\to K^{*}$ form factor ratios at low hadronic recoil from $B\to K^{*}{\ell }^{+}{\ell }^{-}$ data on the angular observables $F_L$, $A_T^{(2)}$ and $P_4^{\prime }$ by adding heavy quark symmetry-based constraints and by investigating the cross talk between low and large recoil. The data-extracted form factor ratios (i) provide benchmarks for the lattice and light-cone sum rule predictions, the latter of which have been updated including improved uncertainty estimations, and (ii) allow us to improve the predictions for benchmark observables. We find that present data on the forward-backward asymmetry $A_{\mathrm{FB}}$ and the angular observable $P_5^{\prime }$ at low recoil are in good agreement with the Standard Model.

We study the QCD evolution of the Sivers effect in both semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan production (DY). We pay close attention to the nonperturbative spin-independent Sudakov factor in the evolution formalism and find a universal form which can describe reasonably well the experimental data on the transverse momentum distributions in SIDIS, DY lepton pair and $W/Z$ production. With this Sudakov factor at hand, we perform a global fitting of all the experimental data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab. We then make predictions for the Sivers asymmetry in DY lepton pair and $W$ production that can be compared to the future experimental measurements to test the sign change of the Sivers functions between SIDIS and DY processes and constrain the sea quark Sivers functions.

The Higgs mechanism may be a quantum phenomenon, i.e., a Coleman-Weinberg potential generated by the explicit breaking of scale symmetry in Feynman loops. We review the relationship of scale symmetry and trace anomalies, and we show that the Coleman-Weinberg potential can be defined as the solution to a differential renormalization group equation that follows from the trace of the improved stress tensor. We propose a simple phenomenological model with “maximal visibility” at the LHC containing a “dormant” Higgs doublet [no VEV, coupled to standard model gauge interactions $SU(2)\times U(1)$] with a mass of $\sim 380\mathrm{GeV}$. We discuss the LHC phenomenology and UV challenges of such a model. We also give a schematic model in which new heavy fermions, with masses $\sim 230\mathrm{GeV}$, can drive a Coleman-Weinberg potential at two loops. The role of the “improved stress tensor” is emphasized, and we propose a nongravitational term, analogous to the $\theta$ term in QCD, which generates it from a scalar action.

Drell-Yan lepton pairs are produced in the process $p\overline{p}\to {\mu }^{+}{\mu }^{-}+X$ through an intermediate ${\gamma }^{*}/Z$boson. The forward-backward asymmetry in the polar-angle distribution of the ${\mu }^{-}$ as a function of the invariant mass of the ${\mu }^{+}{\mu }^{-}$ pair is used to obtain the effective leptonic determination ${\sin }^2{\theta }_{\text{eff}}^{\text{lept}}$ of the electroweak-mixing parameter ${\sin }^2{\theta }_W$, from which the value of ${\sin }^2{\theta }_W$ is derived assuming the standard model. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to $9.2{\mathrm{fb}}^{-1}$ of integrated luminosity from $p\overline{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of ${\sin }^2{\theta }_{\text{eff}}^{\text{lept}}$ is found to be $0.2315\pm 0.0010$, where statistical and systematic uncertainties are combined in quadrature. When interpreted within the context of the standard model using the on-shell renormalization scheme, where ${\sin }^2{\theta }_W=1-M_W^2/M_Z^2$, the measurement yields ${\sin }^2{\theta }_W=0.2233\pm 0.0009$, or equivalently a $W$-boson mass of $80.365\pm 0.047\mathrm{GeV}/c^2$. The value of the $W$-boson mass is in agreement with previous determinations in electron-positron collisions and at the Tevatron collider.

We study the behavior of out of equilibrium retarded, advanced and correlated Green’s functions within the context of an exactly soluble (quenched) model. We show, to the lowest order, that even though the pinch singularities cancel, there is a residual linear dependence on the time interval (after the quench) in the correlated Green’s function which may invalidate perturbation theory. We sum the perturbation series to all orders in this simple model and show explicitly that the complete Green’s functions are well behaved even for large time intervals. The exact form of the correlated Green’s function allows us to extract a manifestly positive distribution function, for large times after the quench, which has a memory of the frequency of the initial system before the quench.