Relativistic Hamiltonians, derived from the path integrals, are known to provide a simple and useful formalism for hadron spectroscopy in QCD. The accuracy of this approach is tested using the QED systems, and the calculated spectrum is shown to reproduce exactly that of the Dirac hydrogen atom, while the Breit-Fermi nonrelativistic expansion is obtained using Foldy-Wouthuizen transformation. The calculated positronium spectrum, including spin-dependent terms, coincides with the standard QED perturbation theory to the considered order $O({\alpha }^4)$.

Here, we provide a simple Hubbard-like model of spin-$1/2$ fermions that gives rise to the SU(2)-symmetric Thirring model that is equivalent, in the low-energy limit, to the Yang-Mills-Chern-Simons model. First, we identify the regime that simulates the SU(2) Yang-Mills theory. Then, we suitably extend this model so that it gives rise to the SU(2) Chern-Simons theory with level $k\ge 2$ that can support non-Abelian anyons. This is achieved by introducing multiple fermionic species and modifying the Thirring interactions, while preserving the SU(2) symmetry. Our proposal provides the means to theoretically and experimentally probe non-Abelian SU(2) level $k$ topological phases.

In this paper we consider conformal dynamics for a system of $N$ interacting relativistic massless particles. A detailed study is done for the case of two particles, with a particular attention to the symmetries of the problem. In fact, we show that this analysis could be extended to the case of higher spin symmetries. Always in the two-particle case a formulation in terms of bilocal fields is proposed. For a system of $N$ particles we consider two possible scenarios: (i) the action is invariant under any permutation of the $N$ particles. This case corresponds to completely democratic interactions with each particle interacting with all the others. The action depends on $N-1$ dimensionless coupling constants. (ii) By putting the particles along a one-dimensional lattice (open or closed) with nearest neighbor interactions, one obtains a model with only two-body interactions depending on a single dimensionless coupling. This model can be easily extended to the continuum case, obtaining a conformal stringlike (closed or open) system.

It is shown that the Wahlquist metric, which is a stationary, axially symmetric perfect fluid solution with $\rho +3p=\text{const}$, admits a rank-2 generalized closed conformal Killing-Yano tensor with a skew-symmetric torsion. Taking advantage of the presence of such a tensor, we obtain a higher-dimensional generalization of the Wahlquist metric in arbitrary dimensions, including a family of vacuum black hole solutions with spherical horizon topology such as Schwarzschild-Tangherlini, Myers-Perry and higher-dimensional Kerr-NUT-(A)dS metrics and a family of static, spherically symmetric perfect fluid solutions in higher dimensions.

We treat a model based upon nonlinear optics for the semiclassical gravitational effects of quantum fields upon light propagation. Our model uses a nonlinear material with a nonzero third order polarizability. Here a probe light pulse satisfies a wave equation containing the expectation value of the squared electric field. This expectation value depends upon the presence of lower frequency quanta, the background field, and modifies the effective index of refraction, and hence the speed of the probe pulse. If the mean squared electric field is positive, then the pulse is slowed, which is analogous to the gravitational effects of ordinary matter. Such matter satisfies the null energy condition and produces gravitational lensing and time delay. If the mean squared field is negative, then the pulse has a higher speed than in the absence of the background field. This is analogous to the gravitational effects of exotic matter, such as stress tensor expectation values with locally negative energy densities, which lead to repulsive gravitational effects, such as defocusing and time advance. We give some estimates of the magnitude of the effects in our model and find that they may be large enough to be observable. We also briefly discuss the possibility that the mean squared electric field could be produced by the Casimir vacuum near a reflecting boundary.

We discuss photon and test-particle orbits in the Kehagias-Sfetsos (KS) metric of Hořava’s gravity. For any value of the Hořava parameter $\omega$, there are values of the gravitational mass $M$ for which the metric describes a naked singularity, and this is always accompanied by a vacuum “antigravity sphere” on whose surface a test particle can remain at rest (in a zero angular momentum geodesic), and inside which no circular geodesics exist. The observational appearance of an accreting KS naked singularity in a binary system would be that of a quasistatic spherical fluid shell surrounded by an accretion disk, whose properties depend on the value of $M$, but are always very different from accretion disks familiar from the Kerr-metric solutions. The properties of the corresponding circular orbits are qualitatively similar to those of the Reissner-Nordström naked singularities. When event horizons are present, the orbits outside the Kehagias-Sfetsos black hole are qualitatively similar to those of the Schwarzschild metric.

We carry out a comprehensive analysis of the simplest curvaton model, which is based on two noninteracting massive fields. Our analysis encompasses cases where the inflaton and curvaton both contribute to observable perturbations, and where the curvaton itself drives a second period of inflation. We consider both power spectrum and non-Gaussianity observables, and focus on presenting constraints in model parameter space. The fully curvaton-dominated regime is in some tension with observational data, while an admixture of inflaton-generated perturbations improves the fit. The inflating curvaton regime mimics the predictions of Nflation. Some parts of parameter space permitted by power spectrum data are excluded by non-Gaussianity constraints. The recent BICEP2 results [P. A. R. Ade et al. (BICEP2 Collaboration), Phys. Rev. Lett. 112, 241101 (2014)], if confirmed as of predominantly primordial origin, require that the inflaton perturbations provide a significant fraction of the total perturbation, ruling out the usual curvaton scenario in which the inflaton perturbations are negligible, though not the admixture regime where both inflaton and curvaton contribute to the spectrum.

We study resonant gravitino production in the early Universe in the presence of SUSY flat directions whose large vacuum expectation values (VEVs) break some but not all gauge symmetries. We find that for a large region of parameter space, the gravitino abundance is several orders of magnitude larger than the cosmological upper bound. Since flat directions with large VEVs are generically expected in supersymmetric theories, this result further exacerbates the gravitino problem.

We study the evolution of various types of biased domain wall networks in the early universe. We carry out larger numerical simulations than those currently available in the literature and provide a more detailed study of the decay of these networks, in particular by explicitly measuring velocities in the simulations. We also use the larger dynamic range of our simulations to test previously suggested decay laws for these networks, including an ad hoc phenomenological fit to earlier simulations and a decay law obtained by Hindmarsh through analytic arguments. We find the latter to be in good agreement with simulations in the case of a biased potential, but not in the case of biased initial conditions.

We investigate potential systematic effects in constraining the amplitude of primordial fluctuations ${\sigma }_8$ arising from the choice of halo mass function in the likelihood analysis of current and upcoming galaxy cluster surveys. We study the widely used $N$-body simulation fit of Tinker et al. (T08) and, as an alternative, the recently proposed analytical model of excursion set peaks (ESP). We first assess the relative bias between these prescriptions when constraining ${\sigma }_8$ by sampling the ESP mass function to generate mock catalogs and using the T08 fit to analyze them, for various choices of survey selection threshold, mass definition and statistical priors. To assess the level of absolute bias in each prescription, we then repeat the analysis on dark matter halo catalogs in $N$-body simulations designed to mimic the mass distribution in the current data release of Planck Sunyaev-Zel’dovich clusters. This $N$-body analysis shows that using the T08 fit without accounting for the scatter introduced when converting between mass definitions (alternatively, the scatter induced by errors on the parameters of the fit) can systematically overestimate the value of ${\sigma }_8$ by as much as $2\sigma$ for current data, while analyses that account for this scatter should be close to unbiased in ${\sigma }_8$. With an increased number of objects as expected in upcoming data releases, regardless of accounting for scatter, the T08 fit could overestimate the value of ${\sigma }_8$ by $\sim 1.5\sigma$. The ESP mass function leads to systematically more biased but comparable results. A strength of the ESP model is its natural prediction of a weak nonuniversality in the mass function which closely tracks the one measured in simulations and described by the T08 fit. We suggest that it might now be prudent to build new unbiased ESP-based fitting functions for use with the larger data sets of the near future.

We improve the sphaleron decoupling condition in the real singlet-extended standard model (SM). The sphaleron energy is obtained using the finite-temperature one-loop effective potential with daisy resummation. For moderate values of the model parameters, the sphaleron decoupling condition is found to be $v_C/T_C>(1.1-1.2)$, where $T_C$ denotes a critical temperature and $v_C$ is the corresponding vacuum expectation value of the doublet Higgs field at $T_C$. We also investigate the deviation of the triple Higgs boson coupling from its standard model value in the region where the improved sphaleron decoupling condition is satisfied. As a result of the improvement, the deviation of the triple Higgs boson coupling gets more enhanced. In a typical case, if the Higgs couplings to the gauge bosons/fermions deviate from the SM values by about 3 (10)%, the deviation of the triple Higgs boson coupling can be as large as about 16 (50)%, which is about 4 (8)% larger than that based on the conventional criterion $v_C/T_C>1$.

Many extensions of the standard model postulate the existence of new weakly coupled particles, the top partners, at or below the TeV scale. The role of the top partners is to cancel the quadratic divergence in the Higgs mass parameter due to top loops. We point out the generic correlation between naturalness (the degree of fine-tuning required to obtain the observed electroweak scale), and the size of top partner loop contributions to Higgs couplings to photons and gluons. If the fine-tuning is required to be at or below a certain level, a model-independent lower bound on the deviations of these Higgs couplings from the standard model can be placed (assuming no cancellations between contributions from various sources). Conversely, if a precise measurement of the Higgs couplings shows no deviation from the standard model, a certain amount of fine-tuning would be required. We quantify this connection, and argue that a measurement of the Higgs couplings at the per cent level would provide a serious and robust test of naturalness.

We discuss the properties and LHC phenomenology of a potentially discoverable heavy scalar boson ($s$) that arises in the context of the renormalizable coloron model; the model also contains a light scalar, $h$, identifiable with the 125 GeV state discovered by the LHC. These two scalar mass eigenstates are admixtures of a weak doublet gauge eigenstate and a weak singlet gauge eigenstate. A previous study set exclusion limits on the heavy $s$ scalar, using the stability of the scalar potential, unitarity, electroweak precision tests, and LHC searches for the 125 GeV Higgs; it also briefly discussed the $\sqrt{s}=7$, 8 TeV LHC searches for a heavy Higgs. In this work, we show how the projected LHC sensitivity at $\sqrt{s}=14\mathrm{TeV}$ to the presence of a heavy Higgs and to the detailed properties of the 125 GeV Higgs will further constrain the properties of the new heavy $s$ scalar. Since the renormalizable coloron model may contain spectator fermions to remove anomalies, we examine several representative scenarios with different numbers of spectator fermions. Our results are summarized in plots that overlay the current exclusion limits on the $s$ boson with the projected sensitivity of the $\sqrt{s}=14\mathrm{TeV}$ LHC to the new state. We find that the upcoming LHC searches should be sensitive to an $s$ scalar of mass less than 1 TeV for essentially all of the model parameter space in which the $h$ state differs from the Higgs boson of the SM. More precisely, unless the mixing between the weak doublet and weak singlet gauge-eigenstate scalars is zero, the 14 TeV LHC will be sensitive to the presence of the nonstandard heavy $s$ state that is characteristic of the renormalizable coloron model.

Pseudoscalar couplings between Standard-Model quarks and dark matter are normally not considered relevant for dark-matter direct-detection experiments because they lead to velocity-suppressed scattering cross sections in the nonrelativistic limit. However, at the nucleon level, such couplings are effectively enhanced by factors of order $\mathcal{O}(m_N/m_q)\sim 10^3$, where $m_N$ and $m_q$ are appropriate nucleon and quark masses, respectively. This enhancement can thus be sufficient to overcome the corresponding velocity suppression, implying—contrary to common lore—that direct-detection experiments can indeed be sensitive to pseudoscalar couplings. In this work, we explain how this enhancement arises, and present a model-independent analysis of pseudoscalar interactions at direct-detection experiments. We also identify those portions of the corresponding dark-matter parameter space which can be probed at current and future experiments of this type, and discuss the role of isospin violation in enhancing the corresponding experimental reach.

Baryon masses at varying values of $N_c$ and light quark masses are studied with lattice QCD and the results are analyzed in a low-energy effective theory based on a combined framework of the $1/N_c$ and heavy baryon chiral perturbation theory expansions. Lattice QCD results for $N_c=3$, 5 and 7 obtained in quenched calculations, as well as results for unquenched calculations for $N_c=3$, are used for the analysis. The results are consistent with a previous analysis of $N_c=3$ lattice QCD results, and in addition permit the determination of subleading in $1/N_c$ effects in the spin-flavor singlet component of the baryon masses, as well as in the hyperfine splittings.

We reinvestigate $K^{*}\mathrm{\Lambda }(1116)$ photoproduction off the nucleon target, based on an effective Lagrangian approach. We include higher nucleon resonances such as $N(2000)5/2^{+}$, $N(2060)5/2^{-}$, $N(2120)3/2^{-}$, and $N(2190)7/2^{-}$, of which the data are taken from the 2012 edition of Review of Particle Physics, in addition to the $t$-channel diagrams ($K$, $K^{*}$, and $\kappa$), the $s$-channel nucleon, and $u$-channel hyperon ($\mathrm{\Lambda }$, $\mathrm{\Sigma }$, and ${\mathrm{\Sigma }}^{*}$) contributions. We find that the $N(2120)3/2^{-}$ and $N(2190)7/2^{-}$ resonances are essential in describing the new CLAS Collaboration data for charged $K^{*}$ photoproduction. On the other hand, they rarely affect neutral $K^{*}$ photoproduction.

We use atmospheric neutrino data and MINOS data to constrain the MaVaN (mass varying neutrinos) mechanism. The MaVaN model was largely studied in cosmology scenarios and comes from the coupling of the neutrinos with a neutral scalar depending on the local matter density. For atmospheric neutrinos, this new interaction affects the neutrino propagation inside the Earth, and as consequence, induces modifications in their oscillation pattern. To perform such test for a nonstandard oscillation mechanism with a nondiagonal neutrino coupling in the mass basis, we analyze the angular distribution of atmospheric neutrino events as seen by the Super-Kamiokande experiment for the events in the sub-GeV and multi-GeV range and muon neutrinos (antineutrinos) in the MINOS experiment. From the combined analysis of these two sets of data we obtain the best fit for $\mathrm{\Delta }{m}_{32}^2=2.45\times {10}^{-3}{\mathrm{eV}}^2$, ${\sin }^2({\theta }_{23})=0.42$ and MaVaN parameter ${\alpha }_{32}=0.28$ with modest improvement, $\mathrm{\Delta }{\chi }^2=1.8$, over the standard oscillation scenario. The combination of MINOS data and Super-Kamiokande data prefers small values of MaVaN parameter ${\alpha }_{32}<0.31$ at 90% C. L.

Responses of surface and underground scintillation detectors of Yakutsk array are calculated for showers initiated by primary particles with energy $E_0\ge 10^{17}\mathrm{eV}$ within the frameworks of QGSJet01d, QGSJet-II-04, SIBYLL-2.1, and EPOS-LHC hadron interaction models. A new estimation of $E_0$ is obtained with the use of various methods. The resulting energy is lower compared to the obtained with earlier method by a factor of $\sim 1.33$.

The hydrodynamic vortex, an effective spacetime geometry for propagating sound waves, is studied analytically. In contrast with the familiar Kerr black hole spacetime, the hydrodynamic vortex model is described by an effective acoustic geometry which has no horizons. However, this acoustic spacetime possesses an ergoregion, a property which it shares with the rotating Kerr spacetime. It has recently been shown numerically that this physical system is linearly unstable due to the superradiant scattering of sound waves in the ergoregion of the effective spacetime. In the present study we use analytical tools in order to explore the onset of these superradiant instabilities which characterize the effective spacetime geometry. In particular, we derive a simple analytical formula which describes the physical properties of the hydrodynamic vortex system in its critical (marginally stable) state, the state which marks the boundary between stable and unstable fluid configurations. The analytically derived formula is shown to agree with the recently published numerical data for the hydrodynamic vortex system.