The $s$-wave pion-kaon ($\pi K$) scattering lengths at zero momentum are calculated in lattice QCD with sufficiently light $u/d$ quarks and strange quark at its physical value by the finite size formula. The light quark masses correspond to $m_{\pi }=0.330–0.466\mathrm{GeV}$. In the Asqtad improved staggered fermion formulation, we measure the $\pi K$ four-point correlators for both the isospin $I=1/2$ and $3/2$ channels, and analyze the lattice simulation data at the next-to-leading order in the continuum three-flavor chiral perturbation theory, which enables a simultaneous extrapolation of $\pi K$ scattering lengths at the physical point. We adopt a technique with the moving wall sources without gauge fixing to obtain substantiable accuracy; moreover, for the $I=1/2$ channel, we employ the variational method to isolate the contamination from the excited states. Extrapolating to the physical point yields the scattering lengths as $m_{\pi }{a}_{3/2}=-0.0512(18)$ and $m_{\pi }{a}_{1/2}=0.1819(35)$ for the $I=3/2$ and $1/2$ channels, respectively. Our simulation results for $\pi K$ scattering lengths are in agreement with the experimental reports and theoretical predictions, and can be comparable with other lattice simulations. These simulations are carried out with MILC $N_f=2+1$ flavor gauge configurations at lattice spacing $a\approx 0.15\mathrm{fm}$.

We demonstrate that it is possible to use the polarization of vector quarkonia, measured from dilepton event samples, as an instrument to study the suppression of ${\chi }_c$ and ${\chi }_b$ in heavy-ion collisions, where a direct determination of signal yields involving the identification of low-energy photons is essentially impossible. A change of the observed $\mathrm{J}/\psi$ and ${\rm Y}(1S)$ polarizations from proton-proton to central nucleus-nucleus collisions would directly reflect differences in the nuclear dissociation patterns of $S$ and $P$ states and may provide a strong indication for quarkonium sequential suppression in the quark-gluon plasma.

We present an extensive study on inhomogeneous chiral condensates in QCD at finite density in the chiral limit using a generalized Ginzburg-Landau (GL) approach. Performing analyses on higher harmonics of one-dimensionally (1D) modulated condensates, we numerically confirm the previous claim that the solitonic chiral condensate characterized by the Jacobi’s elliptic function is the most favorable structure in 1D modulations. We then investigate the possibility of realization of several multidimensional modulations within the same framework. We also study the phase structure far away from the tricritical point by extending the GL functional expanded up to eighth order in the order parameter and its spatial derivative. On the same basis, we explore a new regime in the extended GL parameter space and find that the Lifshitz point is the point where five critical lines meet at once. In particular, the existence of an intriguing triple point is demonstrated, and its trajectory consists of one of those critical lines.

Constituent quark models, while successful, require a great deal of fine-tuning of the short-distance interactions by introducing phenomenological gluonic form factors which are ultimately designed to accurately reproduce the spectrum. We apply and develop renormalization ideas to reduce the short-distance sensitivity and show that, as naively expected, but not explicitly implemented in the models, the physics of binding is entirely linked to the string tension whereas leptonic decays depend more on the gluon exchange potential. We also show how the spectrum of $S$- and $\mathrm{D}\mathrm{\text{−}}{1}^{--}$ states is successfully intertwined through the singular tensor interaction.

Effects of coherence in neutrino production of pions off nuclei are studied employing the color-dipole representation and path integral technique. If the nucleus remains intact, the process is controlled by the interplay of two length scales. One is related to the pion mass and is quite long (at low $Q^2$), while the other, associated with heavy axial-vector states, is much shorter. The Adler relation is found to be broken at all energies, but especially strongly at $\nu \gtrsim 10\mathrm{GeV}$, where the cross section is suppressed by a factor $\sim A^{-1/3}$. On the contrary, in a process where the recoil nucleus breaks up into fragments, the Adler relation turns out to be strongly broken at low energies, where the cross section is enhanced by a factor $\sim A^{1/3}$, but has a reasonable accuracy at higher energies, where all the coherence length scales become long.

The primary motive of parity-violating deep inelastic scattering experiments has been to test the standard model, particularly the axial couplings to the quarks, in the scaling region. The measurements can also test for the validity of models for the off-diagonal structure functions $F_{1,2,3}^{\gamma Z}(x,Q^2)$ in the resonance region. The off-diagonal structure functions are important for the accurate calculation of the $\gamma Z$-box correction to the weak charge of the proton. Currently, with no data to determine $F_{1,2,3}^{\gamma Z}(x,Q^2)$ directly, models are constructed by modifying existing fits to electromagnetic data. We present the asymmetry value for deuteron and proton targets predicted by several different $F_{1,2,3}^{\gamma Z}(x,Q^2)$ models and demonstrate that there are notable disagreements.

The lattice Weinberg-Salam model at zero temperature is investigated numerically. We consider the model for the following values of the coupling constants: the Weinberg angle ${\theta }_W\sim 30°$, the fine structure constant $\alpha \sim (1/150)$, and the Higgs mass $M_H\sim 150\mathrm{GeV}$. We find that the fluctuational region begins at the values of the cutoff $\Lambda$ above about 0.8 TeV. In this region the average distance between Nambu monopoles is close to their sizes. At $\Lambda >1.1\mathrm{TeV}$ the Nambu monopole currents percolate. Within the fluctuational region the considered definitions of the scalar field condensate give values that differ from the expected one $2M_z/g_z$. We consider the given results as an indication that the nonperturbative effects may be present in the Weinberg-Salam model at the large values of the cutoff. Our numerical results were obtained on the lattices of sizes up to ${16}^3\times 32$.

This paper presents a search for standard model Higgs boson production in association with a $W$ boson using events recorded by the CDF experiment in a data set corresponding to an integrated luminosity of $5.6{\mathrm{fb}}^{-1}$. The search is performed using a matrix element technique in which the signal and background hypotheses are used to create a powerful discriminator. The discriminant output distributions for signal and background are fit to the observed events using a binned likelihood approach to search for the Higgs boson signal. We find no evidence for a Higgs boson, and 95% confidence level (C.L.) upper limits are set on $\sigma (p\overline{p}\to WH)\times \mathcal{B}(H\to b\overline{b})$. The observed limits range from 3.5 to 37.6 relative to the standard model expectation for Higgs boson masses between $m_H=100\mathrm{GeV}/c^2$ and $m_H=150\mathrm{GeV}/c^2$. The 95% C.L. expected limit is estimated from the median of an ensemble of simulated experiments and varies between 2.9 and 32.7 relative to the production rate predicted by the standard model over the Higgs boson mass range studied.

It has been shown that very light or even massless neutralinos are consistent with all current experiments, given nonuniversal gaugino masses. Furthermore, a very light neutralino is consistent with astrophysical bounds from supernovae and cosmological bounds on dark matter. Here we study the cosmological constraints on this scenario from big bang nucleosynthesis (taking gravitinos into account) and find that a very light neutralino is even favored by current observations.

We consider the quark-meson model with two quark flavors in a constant external magnetic field $B$ at finite-temperature $T$ and finite baryon chemical potential ${\mu }_B$. We calculate the full renormalized effective potential to one-loop order in perturbation theory. We study the system in the large-$N_c$ limit, where we treat the bosonic modes at tree level. It is shown that the system exhibits dynamical chiral symmetry breaking, i.e. that an arbitrarily weak magnetic field breaks chiral symmetry dynamically, in agreement with earlier calculations using the Nambu–Jona-Lasinio model. We study the influence on the phase transition of the fermionic vacuum fluctuations. For strong magnetic fields, $|qB|\sim 5m_{\pi }^2$ and in the chiral limit, the transition is first order in the entire ${\mu }_B\mathrm{\text{−}}T$ plane if vacuum fluctuations are not included and second order if they are included. At the physical point, the transition is a crossover for ${\mu }_B=0$ with and without vacuum fluctuations.

We show that the symplectic current obtained from the boundary term, which arises in the first variation of a local diffeomorphism invariant action, is covariantly conserved for any gravity theory described by that action. Therefore, a Poincaré invariant two-form can be constructed on the phase space, which is shown to be closed without reference to a specific theory. Finally, we show that one can obtain a charge expression for gravity theories in various dimensions, which plays the role of the Abbott-Deser-Tekin charge for spacetimes with nonconstant curvature backgrounds, by using the diffeomorphism invariance of the symplectic two-form. As an example, we calculate the conserved charges of some solutions of new massive gravity and compare the results with previous works.

We study the gravitational action which is a linear combination of the Hilbert-Palatini term and a term quadratic in torsion and possessing local Poincaré invariance. Although this action yields the same equations of motion as General Relativity, the detailed Hamiltonian analysis without gauge fixing reveals some new points never shown in the Hilbert-Palatini formalism. These include that an additional term containing torsion appears in the spatial diffeomorphism constraint and that the primary second-class constraints have to be imposed in a manner different from that in the Hilbert-Palatini case. These results may provide valuable lessons for further study of Hamiltonian systems with torsion.

We give an exact solution for the static force between two black holes at the turning points in their binary motion. The results are derived by Gibbs’ principle and the Bekenstein-Hawking entropy applied to the apparent horizon surfaces in time-symmetric initial data. New power laws are derived for the entropy jump in mergers, while Newton’s law is shown to derive from a new adiabatic variational principle for the Hilbert action in the presence of apparent horizon surfaces. In this approach, entropy is strictly monotonic such that gravity is attractive for all separations including mergers, and the Bekenstein entropy bound is satisfied also at arbitrarily large separations, where gravity reduces to Newton’s law. The latter is generalized to point particles in the Newtonian limit by application of Gibbs’ principle to world-lines crossing light cones.

In this paper we investigate gravitationally bound, spherically symmetric equilibrium configurations consisting of ordinary (polytropic) matter nonminimally coupled to an external chameleon scalar field. We show that this system has static, regular, asymptotically flat general relativistic solutions. The properties of these spherical configurations, such as total mass, distribution of matter, and size, depend strongly on the surrounding scalar field. The mass is found in terms of the parameter $\sigma$, which is proportional to the central mass density of the ordinary matter. We perform a stability analysis of these spherical solutions and find an upper bound for $\sigma$ where dynamical instability occurs.

Following an earlier suggestion by Dolgov, we present a model of two massless vector fields which dynamically cancel a cosmological constant of arbitrary magnitude and sign. Flat Minkowski spacetime appears asymptotically as an attractor of the field equations. Unlike the original model, the new model does not upset the local Newtonian gravitational dynamics.

We study the spherical, top-hat collapse model for a mixed dark matter model including cold dark matter (CDM) and massive neutrinos of mass scales ranging from $m_{\nu }\simeq 0.05$ to a few 0.1 eV, the range of lower and upper bounds implied from the neutrino oscillation experiments and the cosmological constraints. To develop this model, we properly take into account relative differences between the density perturbation amplitudes of different components (radiation, baryon, CDM, and neutrinos) around the top-hat CDM overdensity region assuming the adiabatic initial conditions. Furthermore, we solve the linearized Boltzmann hierarchy equations to obtain time evolution of the linearized neutrino perturbations, yet including the effect of nonlinear gravitational potential due to the nonlinear CDM and baryon overdensities in the late stage. We find that the presence of massive neutrinos slows down the collapse of CDM (plus baryon) overdensity; however, the neutrinos cannot fully catch up with the nonlinear CDM perturbation due to its large free-streaming velocity for the ranges of neutrino masses and halo masses we consider. We find that, just like CDM models, the collapse time of CDM overdensity is well monitored by the linear theory extrapolated overdensity of CDM plus baryon perturbation, smoothed with a given halo mass scale, if taking into account the suppression effect of the massive neutrinos on the linear growth rate. Using these findings, we argue that the presence of massive neutrinos of mass scales 0.05 or 0.1 eV may cause a significant decrease in the abundance of massive halos compared to the model without the massive neutrinos, e.g., by 25% or factor 2, respectively, for halos with ${10}^{15}{M}_{\odot }$ and at $z=1$.

We use ATLAS and CMS searches in the monojet $+$ missing energy and monophoton $+$ missing energy final state to set limits on the couplings of dark matter to quarks and gluons. Working in an effective field theory framework we compare several existing monojet analyses and find that searches with high $p_T$ cuts are more sensitive to dark matter. We constrain the suppression scale of the effective dark matter–standard model interactions and convert these limits into bounds on the cross sections relevant to direct and indirect detection. We find that, for certain types of operators, in particular, spin-independent dark matter–gluon couplings and spin-dependent dark matter–quark couplings, LHC constraints from the monojet channel are competitive with, or superior to, limits from direct searches up to dark matter masses of order 1 TeV. Comparing to indirect searches, we exclude, at 90% C.L., dark matter annihilating to quarks with the annihilation cross section of a thermal relic for masses below $\sim 15–70\mathrm{GeV}$, depending on the Lorentz structure of the effective couplings. Monophoton limits are somewhat weaker than monojet bounds but still provide an important cross check in the case of a discovery in monojets. We also discuss the possibility that dark matter–standard model interactions at LHC energies cannot be described by effective operators, in which case we find that constraints can become either significantly stronger, or considerably weaker, depending on the mass and width of the intermediate particle. Further, we discuss the special case of dark matter coupling to the Higgs boson, and we show that searches for invisible Higgs decays would provide superior sensitivity, particularly for a light Higgs mass and light dark matter.

We present high-accuracy calculations of the density of states using multicanonical methods for lattice gauge theory with a compact gauge group $U(1)$ on $4^4$, $6^4$, and $8^4$ lattices. We show that the results are consistent with weak and strong coupling expansions. We present methods based on Chebyshev interpolations and Cauchy theorem to find the (Fisher’s) zeros of the partition function in the complex $\beta =1/g^2$ plane. The results are consistent with reweighting methods whenever the latter are accurate. We discuss the volume dependence of the imaginary part of the Fisher’s zeros, the width and depth of the plaquette distribution at the value of $\beta$ where the two peaks have equal height. We discuss strategies to discriminate between first- and second-order transitions and explore them with data at larger volume but lower statistics. Higher statistics and even larger lattices are necessary to draw strong conclusions regarding the order of the transition.

A spin-1 weakly interacting vector boson, $Z^{\prime }$, is predicted by many new physics theories. Searches at colliders for such a $Z^{\prime }$ resonance typically focus on lepton-antilepton or top-antitop events. Here we present a novel channel with a $Z^{\prime }$ resonance that decays to 4 leptons, but not to 2 leptons, and discuss its possible discovery at the Large Hadron Collider. This baryonic gauge boson is well motivated in a supersymmetry framework.

This article introduces a new class of searches for physics beyond the standard model that improves the sensitivity to signals with high jet multiplicity. The proposed searches gain access to high-multiplicity signals by reclustering events into large-radius, or “fat,” jets and by requiring that each event has multiple massive jets. This technique is applied to supersymmetric scenarios in which gluinos are pair-produced and then subsequently decay to final states with either moderate quantities of missing energy or final states without missing energy. In each of these scenarios, the use of jet mass improves the estimated reach in gluino mass by 20% to 50% over current LHC searches.