In this paper, we perform a comprehensive study to probe the effects of large extra dimensions through double Higgs production in proton-proton collisions at the center-of-mass energies of 14, 33, and 100 TeV. We concentrate on the channel in which both Higgs bosons decay into the $b\overline{b}$ pair and take into account the main background contributions through realistic Monte Carlo simulations. In order to achieve an efficient event reconstruction and a good background rejection, jet substructure techniques are used to efficiently capture the boosted Higgs bosons in the final state. The expected limits on the model parameters are obtained based on the invariant mass and the angular properties of the final state objects. Depending on the number of extra dimensions, bounds up to 6.1, 12.5, and 28.1 TeV are set on the model parameter at proton-proton collisions with the center-of-mass energies of 14, 33, and 100 TeV, respectively.

The LHCb Collaboration announced two pentaquark-like structures in the $J/\psi p$ invariant mass distribution. We show that the current information on the narrow structure at 4.45 GeV is compatible with kinematical effects of the rescattering from ${\chi }_{c1}p$ to $J/\psi p$: First, it is located exactly at the ${\chi }_{c1}p$ threshold. Second, the mass of the four-star well-established $\mathrm{\Lambda }(1890)$ is such that a leading Landau singularity from a triangle diagram can coincidentally appear at the ${\chi }_{c1}p$ threshold, and third, there is a narrow structure at the ${\chi }_{c1}p$ threshold but not at the ${\chi }_{c0}p$ and ${\chi }_{c2}p$ thresholds. In order to check whether that structure corresponds to a real exotic resonance, one can measure the process ${\mathrm{\Lambda }}_b^0\to K^{-}{\chi }_{c1}p$. If the $P_c(4450)$ structure exists in the ${\chi }_{c1}p$ invariant mass distribution as well, then the structure cannot be just a kinematical effect but is a real resonance; otherwise, one cannot conclude that $P_c(4450)$ is another exotic hadron. In addition, it is also worthwhile to measure the decay $\mathrm{\Upsilon }(1S)\to J/\psi p\overline{p}$: a narrow structure at 4.45 GeV but not at the ${\chi }_{c0}p$ and ${\chi }_{c2}p$ thresholds would exclude the possibility of a pure kinematical effect.

We construct a holographic model in the framework of Q-lattices whose dual exhibits metal-insulator transitions. By introducing an interacting term between the Q-lattice and the electromagnetic field in bulk geometry, we find such kind of transition can be Mott-like. The evidences are presented as follows. (i) The transition from a metallic phase to an insulating phase occurs when the lattice constant becomes larger. (ii) A hard gap in the insulating phase can be manifestly observed in the optical conductivity. Nevertheless, in the zero temperature limit this model exhibits novel metallic behavior, featured by a gap as well as a zero-frequency mode with tiny spectral weight. It implies that our model is dual to a doped Mott system in one dimension where umklapp scattering is frozen at zero temperature. The similarity between this model and some organic linear chain conductors is briefly discussed.

Several Lagrangians associated with classical limits of Lorentz-violating fermions in the standard model extension (SME) have been shown to yield Finsler functions when the theory is expressed in Euclidean space. When spin couplings are present, the Lagrangian can develop singularities that obstruct the construction of a globally defined Legendre transformation, leading to singular Finsler spaces. A specific sector of the SME where such problems arise is studied. It is found that the singular behavior can be eliminated by an appropriate lifting of the problem to an associated algebraic variety. This provides a smooth classical model for the singular problem. In Euclidean space, the procedure involves combining two related singular Finsler functions into a single smooth function with a semi-positive-definite quadratic form defined on a desingularized variety.

We apply the Lefschetz thimble formulation of field theories to a couple of different problems. We first address the solution of a complex zero-dimensional ${\varphi }^4$ theory. Although very simple, this toy model makes us appreciate a few key issues of the method. In particular, we will solve the model by a correct accounting of all the thimbles giving a contribution to the partition function and we will discuss a number of algorithmic solutions to simulate this (simple) model. We will then move to a chiral random matrix (CRM) theory. This is a somehow more realistic setting, giving us once again the chance to tackle the same couple of fundamental questions: How many thimbles contribute to the solution? How can we make sure that we correctly sample configurations on the thimble? Since the exact result is known for the observable we study (a condensate), we can verify that, in the region of parameters we studied, only one thimble contributes and that the algorithmic solution that we set up works well, despite its very crude nature. The deviation of results from phase quenched ones highlights that in a certain region of parameter space there is a quite important sign problem. In view of this, the success of our thimble approach is quite a significant one.

An exact solution was recently found in the massive gravity theory having the form of Schwarzschild-de Sitter (dS) black holes with some additional background fields. Hawking radiation will occur at the event and cosmological horizons having the blackbody spectrum, which will be modified by the geometry outside the black hole. In this paper, we study the greybody factors of a test scalar, considering its minimal coupling with the background geometry. The case of small black holes with a horizon radius much smaller than the cosmological dS radius is studied numerically. The case of near-extremal black holes with the horizon radius comparable to the cosmological dS radius is studied analytically. In addition, we considered the coupling of the test field with the background Stückelberg fields, which in turn leads to reductions in particle emission and some nontrivial features (resonances) in the greybody factors.

We study the evolution of the cosmological parameters, namely, the deceleration parameter $q(z)$ and the parameter of effective equation of state in a Universe containing, besides ordinary matter and dark energy, a self-interacting (collisional) matter, in the generalized $f(R,T)$ theory of gravity, where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized Friedmann-Robertson-Walker equations and the equation of continuity and obtain a differential equation in $H(z)$, and we solve it numerically for studying the evolution of the cosmological parameters. Two $f(R,T)$ models are considered. The results with collisional matter are compared with the ones of the $\mathrm{\Lambda }$ cold dark matter model, and also with the model where only noncollisional matter exists. The curves show that the models are acceptable because the values found for $w_{\text{eff}}$ are consistent with observed data.

Firstly, we present a reformulation of the standard canonical approach to spherically symmetric systems in which the radial gauge is imposed. This is done via the gauge unfixing technique, which serves as the exposition in the context of the radial gauge. Secondly, we apply the same techniques to the full theory, without assuming spherical symmetry, resulting in a reduced phase space description of general relativity. The canonical structure of the theory is analyzed.

We develop a numerical tool for the fast computation of the temperature and polarization power spectra generated by domain wall networks, by extending the publicly available cmbact code—which calculates the cosmic microwave background signatures generated by active sources—to also describe domain wall networks. In order to achieve this, we adapt the unconnected segment model for cosmic strings to also describe domain wall networks, and use it to model the energy-momentum contribution of domain wall networks throughout their cosmological history. We use this new tool to compute and study the TT, EE, TE and BB power spectra generated by standard domain wall networks, and derive a conservative constraint on the energy scale of the domain wall-forming phase transition of $\eta <0.92\mathrm{MeV}$ (which is a slight improvement over the original Zel’dovich bound of 1 MeV).

We investigate the possibility of observing monochromatic neutrino lines originating from annihilation of dark matter. We analyze several astrophysical sources with overdensities of dark matter that can amplify the signal. As a case study, we consider mixed left- and right-handed sneutrino dark matter. We demonstrate that in the physically viable region of the model, one can obtain a prominent monochromatic neutrino line. We propose a search strategy to observe these neutrino lines in future generations of neutrino telescopes that is especially sensitive to dwarf spheroidal galaxies. We demonstrate that the presence of massive black holes in the cores of dwarfs as well as of more massive galaxies substantially boosts any putative signal. In particular, dark matter in dwarf galaxies spiked by an intermediate massive black hole provides a powerful means of probing low-annihilation cross sections well below ${10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ that are otherwise inaccessible by any future direct detection or collider experiment.

We construct an equilibrium partition function for a nonrelativistic fluid and use it to constrain the dynamics of the system. The construction is based on light cone reduction, which is known to reduce the Poincaré symmetry to Galilean in one lower dimension. We modify the constitutive relations of a relativistic fluid, and find that its symmetry broken phase—“null fluid” is equivalent to the nonrelativistic fluid. In particular, their symmetries, thermodynamics, constitutive relations, and equilibrium partition function match exactly to all orders in derivative expansion.

We study the implications of the ELKO fermions as a cold dark matter candidate. Such fermions arise in theories that are not symmetric under the full Lorentz group. Although they do not carry electric charge, ELKOs can still couple to photons through a nonstandard interaction. They also couple to the Higgs but do not couple to other standard model particles. We impose limits on their coupling strength and the ELKO mass assuming that these particles give dominant contribution to the cosmological cold dark matter. We also determine limits imposed by the direct dark matter search experiments on the ELKO-photon and the ELKO-Higgs coupling. Furthermore we determine the limit imposed by the gamma ray bursts time delay observations on the ELKO-Higgs coupling. We find that astrophysical and cosmological considerations rule out the possibility that ELKO may contribute significantly as a cold dark matter candidate. The only allowed scenario in which it can contribute significantly as a dark matter candidate is that it was never in equilibrium with the cosmic plasma. We also obtain a relationship between the ELKO self-coupling and its mass by demanding it to be consistent with observations of dense cores in the galactic centers.

We explore $CP$ violating aspects in the Higgs sector of models where new vectorlike quarks carry Yukawa couplings mainly to the third generation quarks of the Standard Model. We point out that in the simplest model, Higgs $CP$ violating interactions only exist in the $hWW$ channel. At low energy, we find that rare $B$ decays can place similarly strong constraints as those from electric dipole moments on the source of $CP$ violation. These observations offer a new handle to discriminate from other Higgs $CP$ violating scenarios such as scalar sector extensions of the Standard Model, and imply an interesting future interplay among limits from different experiments.

We examine the leptophilic two-Higgs-doublet model with fermionic dark matter, considering the range of experimental constraints on the Higgs sector. The measurements of the 125 GeV Higgs from the LHC run I allow us to focus on those remaining processes that may play an important role at colliders. We find that the leptophilic model allows for a much lighter Higgs than in other two-Higgs models, although discovery at the LHC will be difficult. Adding a dark matter sector motivated by supersymmetric extensions of the leptophilic model, we find the existing parameter space can accommodate constraints from direct detection and the invisible widths of the Higgs and $Z$, while also fitting the Galactic Center gamma ray excess reported by analyses of Fermi-LAT data. We also discuss the status of the fully supersymmetric version of such models, which include four Higgs doublets and a natural dark matter candidate.

We study finite (physical) volume and scaling violation effects of the Landau gauge ghost propagator as well as of the running coupling ${\alpha }_s(p)$ in the $SU(2)$ lattice gauge theory. We consider lattices with physical linear sizes between $aL\simeq 3$ and $aL\simeq 7\mathrm{fm}$ and values of lattice spacing between $a=0.2$ and $a=0.07\mathrm{fm}$. To fix the gauge we apply an efficient gauge fixing method aimed at finding extrema as close as possible to the global maximum of the gauge functional. We find finite volume effects to be small for the lattice size $aL\simeq 3\mathrm{fm}$ at momenta $|p|\gtrsim 0.6\mathrm{GeV}$. For the same lattice size we study extrapolations to the continuum limit of the ghost dressing function as well as for the running coupling with momenta chosen between $|p|=0.41$ and $|p|=3.2\mathrm{GeV}$. We present fit formulas for the continuum limit of both observables in this momentum range. Our results testify in favor of the decoupling behavior in the infrared limit.

We investigate the potential for the Deep Underground Neutrino Experiment (DUNE) to probe the existence and effects of a fourth neutrino mass eigenstate. We study the mixing of the fourth mass eigenstate with the three active neutrinos of the Standard Model, including the effects of new sources of $CP$-invariance violation, for a wide range of new mass-squared differences, from lower than ${10}^{-5}{\mathrm{eV}}^2$ to higher than $1{\mathrm{eV}}^2$. DUNE is sensitive to previously unexplored regions of the mixing angle–mass-squared difference parameter space. If there is a fourth neutrino, in some regions of the parameter space, DUNE is able to measure the new oscillation parameters (some very precisely) and clearly identify two independent sources of $CP$-invariance violation. Finally, we use the hypothesis that there are four neutrino mass eigenstates in order to ascertain how well DUNE can test the limits of the three-massive-neutrinos paradigm. In this way, we briefly explore whether light sterile neutrinos can serve as proxies for other, in principle unknown, phenomena that might manifest themselves in long-baseline neutrino oscillation experiments.

The second generation of interferometric gravitational wave detectors are quickly approaching their design sensitivity. For the first time these detectors will become limited by quantum backaction noise. Several backaction evasion techniques have been proposed to further increase the detector sensitivity. Since most proposals rely on a flexible readout of the full amplitude- and phase-quadrature space of the output light field, balanced homodyne detection is generally expected to replace the currently used DC readout. Up to now, little investigation has been undertaken into how balanced homodyne detection can be successfully transferred from its ubiquitous application in tabletop quantum optics experiments to large-scale interferometers with suspended optics. Here we derive implementation requirements with respect to local-oscillator noise couplings and highlight potential issues with the example of the Glasgow Sagnac Speed Meter experiment, as well as for a future upgrade to the Advanced LIGO detectors.

The $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section and charged-kaon electromagnetic form factor are measured in the $e^{+}{e}^{-}$ center-of-mass energy range ($E$) from 2.6 to 8.0 GeV using the initial-state radiation technique with an undetected photon. The study is performed using $469{\mathrm{fb}}^{-1}$ of data collected with the BABAR detector at the PEP-II2 $e^{+}{e}^{-}$ collider at center-of-mass energies near 10.6 GeV. The form factor is found to decrease with energy faster than $1/E^2$ and approaches the asymptotic QCD prediction. Production of the $K^{+}{K}^{-}$ final state through the $J/\psi$ and $\psi (2S)$ intermediate states is observed. The results for the kaon form factor are used together with data from other experiments to perform a model-independent determination of the relative phases between electromagnetic (single-photon) and strong amplitudes in $J/\psi$ and $\psi (2S)\to K^{+}{K}^{-}$ decays. The values of the branching fractions measured in the reaction $e^{+}{e}^{-}\to K^{+}{K}^{-}$ are shifted relative to their true values due to interference between resonant and nonresonant amplitudes. The values of these shifts are determined to be about $\pm 5\%$ for the $J/\psi$ meson and $\pm 15\%$ for the $\psi (2S)$ meson.