We apply Schrödinger functional methods to two gauge theories with fermions in two-index representations: the SU(3) theory with $N_f=2$ adjoint fermions, and the SU(4) theory with $N_f=6$ fermions in the two-index antisymmetric representation. Each theory is believed to lie near the bottom of the conformal window for its respective representation. In the SU(3) theory we find a small beta function in strong coupling but we cannot confirm or rule out an infrared fixed point. In the SU(4) theory we find a hint of walking—a beta function that approaches the axis and then turns away from it. In both theories the mass anomalous dimension remains small even at the strongest couplings, much like the theories with fermions in the two-index symmetric representation investigated earlier.

We present the first practical Monte Carlo calculations of the recently proposed Lefschetz thimble formulation of quantum field theories. Our results provide strong evidence that the numerical sign problem that afflicts Monte Carlo calculations of models with complex actions can be softened significantly by changing the domain of integration to the Lefschetz thimble or approximations thereof. We study the interacting complex scalar field theory (relativistic Bose gas) in lattices of size up to $8^4$ using a computationally inexpensive approximation of the Lefschetz thimble. Our results are in excellent agreement with known results. We show that—at least in the case of the relativistic Bose gas—the thimble can be systematically approached and the remaining residual phase leads to a much more tractable sign problem (if at all) than the original formulation. This is especially encouraging in view of the wide applicability—in principle—of our method to quantum field theories with a sign problem. We believe that this opens up new possibilities for accurate Monte Carlo calculations in strongly interacting systems of sizes much larger that previously possible.

We present time-dependent exact solutions composed of F-strings intersecting D2-branes in type IIA supergravity. The F-strings tend to approach each other with time in the six-dimensional space transverse to both F-strings and D2-branes. In general, a singularity appears before collision. An exceptional case is that the charges are the same and five directions in the transverse space are smeared out. Then we argue some applications of the solutions in building cosmological models. The possible models are classified based on compactifications of the internal space. All of them give rise to the Friedmann-Robertson-Walker universe with a power-law expansion.

We develop a general set of methods for computing the oblique electroweak parameters $S$ and $T$ for bottom-up and top-down motivated scenarios in which the Higgs weakly mixes with a superconformal extra sector. In addition to their utility in phenomenological studies, the observables $S$ and $T$ are also of purely theoretical interest as they are defined by correlation functions of broken symmetries. We show that in the limit where the extra sector enjoys an approximate custodial symmetry, the leading contributions to $S$ and $T$ can be recast as calculable data of the theory in the conformal phase. Using this result, we also obtain model-independent bounds on the sign and size of oblique electroweak corrections from unitary superconformal theories.

Wave propagation in nonlinear theories of the electromagnetism described by Lagrangian densities dependent upon its two local invariants $L(F,G)$ is revisited. On the light of the recent findings in metamaterials, it is here shown that trirefringence is also a possible phenomenon to occur in the realm of such nonlinear theories. A specific model exhibiting this effect is investigated in terms of both phase and group velocities. It is claimed that wave propagation in some well known nonlinear models for spin-one fields, like QED and QCD in certain regimes, may exhibit trirefringence.

We investigate nonperturbative infrared effects for the $O(N)$ linear sigma model in de Sitter space using the two-particle irreducible effective action at the Hartree truncation level. This approximation resums the infinite series of so-called superdaisy diagrams. For the proper treatment of ultraviolet divergences, we first study the renormalization of this approximation on a general curved background. Then, we calculate radiatively corrected masses and the effective potential. As a result, spontaneous symmetry breaking is possible; on the other hand, the Goldstone modes acquire a positive definite mass term due to the screening effects of interaction. Possible infrared divergence is self-regulated by the mass term. Furthermore, there is a symmetry-restoring phase transition as a function of the Hubble parameter. In our approximation, the phase transition is of first order.

We analyze quantized scalar, spinor, and photon fields in a mechanically rigid cavity that is accelerated in Minkowski spacetime, in a recently introduced perturbative small-acceleration formalism that allows the velocities to become relativistic, with a view to applications in relativistic quantum information. A scalar field is analyzed with both Dirichlet and Neumann boundary conditions, and a photon field under perfect conductor boundary conditions is shown to decompose into Dirichlet-like and Neumann-like polarization modes. The Dirac spinor is analyzed with a nonvanishing mass and with dimensions transverse to the acceleration, and the MIT bag boundary condition is shown to exclude zero modes. Unitarity of time evolution holds for smooth accelerations but fails for discontinuous accelerations in spacetime dimensions ($3+1$) and higher. As an application, the experimental desktop mode-mixing scenario proposed for a scalar field by Bruschi et al. [New. J. Phys. 15, 073052 (2013)] is shown to apply also to the photon field.

We derive the simplest traversable wormhole solutions in $n$-dimensional general relativity, assuming static and spherically symmetric space-time with a ghost scalar field. This is the generalization of the Ellis solution (or the so-called Morris-Thorne’s traversable wormhole) into a higher dimension. We also study their stability using linear perturbation analysis. We obtain the master equation for the perturbed gauge-invariant variable and search their eigenvalues. Our analysis shows that all higher dimensional wormholes have an unstable mode against the perturbations with which the throat radius is changed. The instability is consistent with the earlier numerical analysis in the four-dimensional solution.

We present a coupled channel unitary approach to obtain states dynamically generated from the meson-baryon interaction with hidden charm, using constraints of heavy quark spin symmetry. As a basis of states, we use $\overline{D}B$, ${\overline{D}}^{*}B$ states, with $B$ baryon charmed states belonging to the 20 representations of SU(4) with $J^P=1/2^{+}$, $3/2^{+}$. In addition we also include the ${\eta }_{c}N$ and $J/\psi N$ states. The inclusion of these coupled channels is demanded by heavy quark spin symmetry, since in the large $m_Q$ limit the $D$ and $D^{*}$ states are degenerate and are obtained from each other by means of a spin rotation, under which QCD is invariant. The novelty in the work is that we use dynamics from the extrapolation of the local hidden gauge model to SU(4), and we show that this dynamics fully respects the constraints of heavy quark spin symmetry. With the full space of states demanded by the heavy quark spin symmetry and the dynamics of the local hidden gauge, we look for states dynamically generated and find four basic states that are bound, corresponding to $\overline{D}{\Sigma }_c$, $\overline{D}{\Sigma }_c^{*}$, ${\overline{D}}^{*}{\Sigma }_c$, and ${\overline{D}}^{*}{\Sigma }_c^{*}$, decaying mostly into ${\eta }_{c}N$ and $J/\psi N$. All the states appear in isospin $I=1/2$, and we find no bound states or resonances in $I=3/2$. The $\overline{D}{\Sigma }_c$ state appears in $J=1/2$ and the $\overline{D}{\Sigma }_c^{*}$ in $J=3/2$; the ${\overline{D}}^{*}{\Sigma }_c$ appears nearly degenerate in $J=1/2$, $3/2$ and the ${\overline{D}}^{*}{\Sigma }_c^{*}$ appears nearly degenerate in $J=1/2$, $3/2$, $5/2$, with the peculiarity that in $J=5/2$ the state has zero width in the space of states chosen. All the states are bound with about 50 MeV with respect to the corresponding $\overline{D}B$ thresholds, and the width, except for the $J=5/2$ state, is also of the same order of magnitude. Finally, we discuss the uncertainties stemming from the expected breaking of SU(4) and the heavy quark spin symmetry.

We prove that Borel QCD sum rules for heavy–light currents yield very strong correlations between the $b$-quark mass $m_b$ and the $B$-meson decay constant $f_B$, namely, $\delta f_B/f_B\approx -8\delta m_b/m_b$. This fact opens the possibility of an accurate sum-rule extraction of $m_b$ by using $f_B$ as input. Combining precise lattice QCD determinations of $f_B$ with our sum-rule analysis based on the three-loop $O({\alpha }_s^2)$ heavy–light correlation function leads to ${\overline{m}}_b({\overline{m}}_b)=(4.247\pm 0.034)\mathrm{GeV}$.

We explore the MSSM with nine free parameters (p9MSSM) that have been selected as a minimum set that allows an investigation of neutralino dark matter and collider signatures while maintaining consistency with several constraints. These include measurement of the dark matter relic density from PLANCK, main properties of the discovered Higgs boson, LHC direct supersymmetry searches, recent evidence for a Standard Model–like $\mathrm{\text{branching ratio}}\mathrm{BR}(B_s\to {\mu }^{+}{\mu }^{-})$, and the measurement of $\delta (g-2{)}_{\mu }$, plus a number of other electroweak and flavor physics constraints. We perform a simulation of two LHC direct supersymmetry searches at $\sqrt{s}=8\mathrm{TeV}$: the CMS inclusive ${\alpha }_T$ search for squarks and gluinos and the CMS electroweak production search with $3l+E_T^{\mathrm{miss}}$ in the final state. We use the latter to identify the regions of the parameter space, consistent at $2\sigma$ with $\delta (g-2{)}_{\mu }$, that are not excluded by the direct limits from the electroweak production. We find that they correspond to a neutralino mass in the window $200\mathrm{GeV}\lesssim m_{\chi }\lesssim 500\mathrm{GeV}$. We also implement the likelihood for the XENON100 exclusion bound, in which we consider for the first time the impact of a recent determination of the ${\Sigma }_{\pi N}$ term from CHAOS data, ${\Sigma }_{\pi N}=43\pm 12\mathrm{MeV}$. We show that in light of this measurement, the present statistical impact of the XENON100 bound is greatly reduced, although future sensitivities of the LUX and XENON1T experiments will have decisive impact on the mixed bino/Higgsino composition of the neutralino. We point out some tension between the constraints from $\delta (g-2{)}_{\mu }$ and XENON100. Finally, we present prospects for various indirect searches of dark matter, namely $\gamma$-ray fluxes from dSphs and the Galactic Center at Fermi-LAT, and the positron flux at AMS02. We also show the five-year sensitivity on the spin-dependent neutralino-proton cross section due to neutrino fluxes from the Sun at IceCube.

In lattice QCD, color confinement manifests in flux tubes. We compute in detail the quark-antiquark flux tube for pure gauge SU(3) dimension $D=3+1$ for quark-antiquark distances $R$ ranging from 0.4 to 1.4 fm. To increase the signal-to-noise ratio, we apply the improved multihit and extended smearing techniques. We detail the gauge-invariant squared components of the color electric and color magnetic fields both in the mediator plane between the static quark and static antiquark and in the planes of the charges. We fit the field densities with appropriate Ansätze, and we observe the screening of the color fields in all studied planes together with the quantum widening of the flux tube in the mediator plane. All components squared of the color fields are nonvanishing and are consistent with a penetration length $\lambda \sim 0.22$ to 0.24 fm and an effective screening mass $\mu \sim 0.8$ to 0.9 GeV. The quantum widening of the flux tube is well fitted with a logarithmic law in $R$.

We introduce a nonperturbative, first-principles numerical approach for solving time-dependent problems in quantum field theory, using light-front quantization. As a first application we consider QED in a strong background field, and the process of nonlinear Compton scattering in which an electron is excited by the background and emits a photon. We track the evolution of the quantum state as a function of time. Observables, such as the invariant mass of the electron-photon pair, are first checked against results from perturbation theory, for suitable parameters. We then proceed to a test case in the strong background field regime and discuss the various nonperturbative effects revealed by the approach.

In canonical gravity, the choice of a local time direction is not obviously compatible with local Lorentz invariance. One way to address this issue is to view gravity as a gauge theory on observer space, rather than spacetime. In a Lorentz covariant theory, observer space is the space of unit future-directed timelike vectors; picking such a vector locally breaks the symmetry to a subgroup $\mathrm{SO}(D)$ of $\mathrm{SO}(D,1)$, so that on observer space the local symmetry group is $\mathrm{SO}(D)$. Observer space geometries naturally describe any gravitational theory that only assumes local invariance under $\mathrm{SO}(D)$. Here we construct nonrelativistic observer spaces for gravity with a fixed foliation, applicable to preferred foliation theories such as Hořava–Lifshitz gravity. Different Hořava–Lifshitz observers at a point are related by a change in the shift vector, leaving the preferred foliation invariant. Gravity is formulated on a nonrelativistic frame bundle with structure group $\mathrm{ISO}(D)$; the shift vector acts as a symmetry breaking field breaking $\mathrm{ISO}(D)$ symmetry spontaneously to $\mathrm{SO}(D)$. A natural torsion-free connection is constructed, including the usual $\mathrm{SO}(D,1)$ connection of relativistic gravity plus terms depending on derivatives of the shift vector. This observer space geometry provides a novel geometric framework for the study of preferred foliation theories.

We derive multipolar equations of motion for gravitational theories with general nonminimal coupling in spacetimes admitting torsion. Our very general findings allow for the systematic testing of whole classes of theories by means of extended test bodies. One peculiar feature of certain subclasses of nonminimal theories turns out to be their sensitivity to post-Riemannian spacetime structures even in experiments without microstructured test matter.

Searches for dispersive effects in the propagation of light at cosmological distances have been touted as sensitive probes of Lorentz invariance violation (LIV) and of theories of quantum gravity. Frequency-dependent time lags between simultaneously emitted pulses of light can signal a modification in the photon dispersion relation; however, matter engenders the cosmos with a dispersive index of refraction to similar effect. We construct a theoretical framework for the analysis of such effects, contrasting these dispersive terms with those from LIV models. We consider all matter, both luminous and dark. Though the only known mode of interaction for dark matter (DM) is gravitational, most models of dark matter also allow for electromagnetic interactions, if only at the one-loop level in perturbation theory. Generically, the leading order dispersive effects due to matter scale with photon energy as ${\omega }^{-2}$ for a charged DM candidate and ${\omega }^2$ for a neutral DM candidate. Terms linear in $\omega$ can arise in the index of refraction if parity and charge-parity asymmetries are present at the Lagrangian or system level. Herein, we compute the index of refraction for a millicharged dark matter candidate at the one-loop level, a neutral scalar DM candidate introduced by Boehm and Fayet [Nucl. Phys. B 683, 219 (2004)], and the minimal supersymmetric standard model’s neutralino. For a neutral DM candidate, we determine that matter effects can compete with LIV effects that depend quadratically on energy whenever the photon energy is beyond ${10}^{29}\mathrm{GeV}$, well beyond the Greisen-Zatsepin-Kuzmin cutoff. The dispersive matter effects that scale linearly with $\omega$ are model dependent, and their existence results in circular birefringence.

We present a dark matter model reproducing well the results from DAMA/LIBRA and CoGeNT and having no contradiction with the negative results from XENON100 and CDMS-II/Ge. Two new species of fermions $F$ and $G$ form hydrogenlike atoms with standard atomic size through a dark $U(1)$ gauge interaction carried out by a dark massless photon. A Yukawa coupling between the nuclei $F$ and neutral scalar particles $S$ induces an attractive shorter-range interaction. This dark sector interacts with our standard particles because of the presence of two mixings, a kinetic photon–dark photon mixing, and a mass $\sigma \mathrm{\text{−}}S$ mixing. The dark atoms from the halo diffuse elastically in terrestrial matter until they thermalize and then reach underground detectors with thermal energies, where they form bound states with nuclei by radiative capture. This causes the emission of photons that produce the signals observed by direct-search experiments.

We consider a Friedmann-Robertson-Walker universe with a fluid source obeying a nonideal equation of state with ‘‘asymptotic freedom,” namely ideal gas behavior (pressure changes directly proportional to density changes) both at low and high density regimes, following a fluid dynamical model due to Shan and Chen. It is shown that, starting from an ordinary energy density component, such fluids naturally evolve towards a universe with a substantial ‘‘dark energy” component at the present time, with no need of invoking any cosmological constant. Moreover, we introduce a quantitative indicator of darkness abundance, which provides a consistent picture of the actual matter-energy content of the Universe.