New vectorlike fermions that mix with the third generation can significantly affect the $\tau$ and $b$ Yukawa couplings. Consistent with precision electroweak measurements, the width of the Higgs boson to $\tau \tau$, $b\overline{b}$ can be reduced by $\mathcal{O}(1)$ with respect to the Standard Model values. In the case of the $b$ quark, a reduced width would result in an enhanced branching ratio for other final states, such as $\gamma \gamma$. New leptons can also substantially modify the Higgs boson branching ratio to photons through radiative effects, while new quarks can contribute to $gg$ fusion. The combined effect can be as much as a factor of two on the branching ratio to $\gamma \gamma$. The new quarks and leptons could be light, which would allow discovery at the LHC. In the case of significant suppression of $h\to \tau \tau$, searches for new leptons decaying to $\tau$-rich final states, perhaps in association with Higgs bosons, are motivated.

We propose octahedral group $O_h$ as the family symmetry of the neutrino-lepton sector. We find that $O_h$ contains subgroups ${\mathbb{Z}}_2^{\mu \tau }\otimes {\mathbb{Z}}_2^s$ and ${\mathbb{Z}}_4^{\ell }$ for realizing the bimaximal (BM) mixings ${\theta }_{23}={\theta }_{12}=45°$, where ${\mathbb{Z}}_2^{\mu \tau }\otimes {\mathbb{Z}}_2^s$ and ${\mathbb{Z}}_4^{\ell }$ serve as the residual symmetries of neutrinos and charged leptons, respectively. We present geometric interpretations of BM mixing in the octahedron, and construct natural geometrical breaking of ${\mathbb{Z}}_4^{\ell }$, leading to nontrivial deviations from the BM mixings. Our theory makes truly simple predictions of a relatively large reactor angle, ${\theta }_{13}\simeq 45°-{\theta }_{12}=7.5°–13.7°$ $(3\sigma )$, the nearly maximal atmospheric angle and the approximate maximal Dirac $CP$ violation. These agree well with the current neutrino data, and will be further probed by the on-going and upcoming oscillation experiments.

We consider a braneworld model in the scalar-tensor gravity. In order to solve the gauge hierarchy problem in this model, our world should be confined on the positive tension brane rather than on the negative one. This is crucial to reproduce a correct Friedmann-like equation on the brane. Interestingly, it is found that the spacing of mass spectrum in this scenario is very tiny, but the light gravitons cannot be observed individually in colliders because of their sufficiently weak interaction with matter fields on the visible brane.

We present a Chern-Simons action for $\mathrm{N}=2$ super-Yang-Mills theory in “full” $\mathrm{N}=2$ superspace (hyperspace) augmented by coordinates of the internal SU(2) group and show that this action can be reduced to the usual super-Yang-Mills action in the Harmonic () hyperspace. We also discover that the “choice” of Harmonic hyperspace is not unique and under suitable conditions, further reduction to the well-known Projective ($\check{\Pi }$) hyperspace is possible.

We investigate the effects of explicit breaking of Z(3) symmetry due to the presence of dynamical quarks on the formation and evolution of Z(3) walls and associated quark-gluon plasma (QGP) strings within the Polyakov loop model. We carry out numerical simulations of the first order quark-hadron phase transition via bubble nucleation (which may be appropriate, for example, at finite baryon chemical potential) in the context of relativistic heavy-ion collision experiments. Using appropriate shifting of the order parameter in the Polyakov loop effective potential, we calculate the bubble profiles using the bounce technique for the true vacuum as well as for the metastable Z(3) vacua, and estimate the associated nucleation probabilities. These different bubbles are then nucleated and evolved, and the resulting formation and dynamics of Z(3) walls and QGP strings are studied. We discuss various implications of the existence of these Z(3) interfaces and the QGP strings, especially in view of the effects of the explicit breaking of the Z(3) symmetry on the formation and dynamical evolution of these objects.

We show that a single imperfect fluid can be used as a source to obtain a mass-varying black hole in an expanding universe. This approach generalizes the well-known McVittie spacetime, by allowing the mass to vary thanks to a novel mechanism based on the presence of a temperature gradient. This fully dynamical solution, which does not require phantom fields or fine-tuning, is a step forward in a new direction in the study of systems whose local gravitational attraction is coupled to the expansion of the universe. We present a simple but instructive example for the mass function and briefly discuss the structure of the apparent horizons and the past singularity.

We study perturbations around some cosmological backgrounds in the de Rham-Gabadadze-Tolley theory of massive gravity. We develop a general formalism to calculate the perturbations around any background. We derive the Lagrangian for fluctuations in the small-scale limit, and for the open Friedman-Robertson-Walker solution we repeat the analysis around the full background. We find that the perturbations display similar properties: the longitudinal modes of the massive graviton are instantaneous at quadratic level, but they acquire a kinetic term at cubic order.

We study field theories in two spacetime dimensions invariant under a chiral scaling symmetry that acts only on right-movers. The local symmetries include one copy of the Virasoro algebra and a U(1) current algebra. This differs from the two-dimensional conformal group but in some respects is equally powerful in constraining the theory. In particular, the symmetries on a torus lead to modular covariance of the partition function, which is used to derive a universal formula for the asymptotic density of states. For an application we turn to the holographic description of black holes in quantum gravity, motivated by the fact that the symmetries in the near-horizon geometry of any extremal black hole are identical to those of a two-dimensional field theory with chiral scaling. We consider two examples: black holes in warped ${\mathrm{AdS}}_3$ in topologically massive gravity and in string theory. In both cases, the density of states in the two-dimensional field theory reproduces the Bekenstein-Hawking entropy of black holes in the gravity theory.

Standard fundamental equations of motion for point particles are of second order in the time derivative. Here we are exploring the consequences of fundamental equations of motion with an additional small even higher order term to the standard formulation. This is related to two issues: (i) higher order equations of motion will have influence on the definition of the structure of possible interactions and in particular of the gravitational interaction, and (ii) such equations of motion provide a framework to test the validity of Newton’s second law which is the basis for the definition of forces but which assumes from the very beginning that the fundamental equations of motion are of second order. We will show that starting with our generalized equations of motions it is possible to introduce the space-time metric describing the gravitational interaction by means of a standard gauge principle. Another main result within our model of even higher order derivatives is that for slowly varying and smooth fields the higher order derivatives either lead to runaway solutions or induces a zitterbewegung. We confront this higher order scheme with experimental data.

We use the Szekeres inhomogeneous cosmological models to study the growth of large-scale structure in the universe including nonzero spatial curvature and a cosmological constant. In particular, we use the Goode and Wainwright formulation of the solution, as in this form the models can be considered to represent exact nonlinear perturbations of an averaged background. We identify a density contrast in both classes I and II of the models, for which we derive growth evolution equations. By including $\Lambda$, the time evolution of the density contrast as well as kinematic quantities of interest can be tracked through the matter- and $\Lambda$-dominated cosmic eras up to the present and into the future. In class I, we consider a localized cosmic structure representing an overdensity neighboring a central void, surrounded by an almost Friedmann-Lemaître-Robertson-Walker background, while for class II, the exact perturbations exist globally. In various models of class I and class II, the growth rate is found to be stronger in the matter-dominated era than that of the standard lambda-cold dark matter ($\Lambda \mathrm{CDM}$) cosmology, and it is suppressed at later times due to the presence of the cosmological constant. We find that there are Szekeres models able to provide a growth history similar to that of $\Lambda \mathrm{CDM}$ while requiring less matter content and nonzero spatial curvature, which speaks to the importance of including the effects of large-scale inhomogeneities in analyzing the growth of large-scale structure. Using data for the growth factor $f$ from redshift space distortions and the Lyman-$\alpha$ forest, we obtain best fit parameters for class II models and compare their ability to match observations with $\Lambda \mathrm{CDM}$. We find that there is negligible difference between best fit Szekeres models with no priors and those for $\Lambda \mathrm{CDM}$, both including and excluding Lyman-$\alpha$ data. We also find that the standard growth index $\gamma$ parametrization cannot be applied in a simple way to the growth in Szekeres models, so a direct comparison of the function $f$ to the data is performed. We conclude that the Szekeres models can provide an exact framework for the analysis of large-scale growth data that includes inhomogeneities and allows for different interpretations of observations.

In the framework of Hořava-Lifshitz theory, we study the eigenvalues associated with the Wheeler-DeWitt equation representing the vacuum expectation values associated with the cosmological constant. The explicit calculation is performed with the help of a variational procedure with trial wave functionals of the Gaussian type. We analyze both the case with the detailed balanced condition and the case without it. In the case without the detailed balance, we find the existence of an eigenvalue depending on the set of coupling constants ($g_2$, $g_3$) and ($g_4$, $g_5$, $g_6$), respectively, and on the physical scale.

The measurements of the 21-cm brightness temperature fluctuations from the neutral hydrogen at the Epoch of Reionization should inaugurate the next generation of cosmological observables. In this respect, many works have concentrated on the disambiguation of the cosmological signals from the dominant reionization foregrounds. However, even after perfect foregrounds removal, our ignorance on the background reionization history can significantly affect the cosmological parameter estimation. In particular, the interdependence between the hydrogen ionized fraction, the baryon density and the optical depth to the redshift of observation induce nontrivial degeneracies between the cosmological parameters that have not been considered so far. Using a simple but consistent reionization model, we revisit their expected constraints for a futuristic giant 21-cm omniscope by using for the first time Markov Chain Monte Carlo methods on multiredshift full sky simulated data. Our results agree well with the usual Fisher matrix analysis on the three-dimensional flat sky power spectrum but only when the above-mentioned degeneracies are kept under control. In the opposite situation, Fisher results can be inaccurate. We show that these conditions can be fulfilled by combining cosmic microwave background measurements with multiple observation redshifts probing the beginning of the Epoch of Reionization. This allows a precise reconstruction of the total optical depth, reionization duration and maximal spin temperature. Finally, we discuss the robustness of these results in presence of unresolved ionizing sources. Although most of the standard cosmological parameters remain weakly affected, we find a significant degradation of the background reionization parameter estimation in presence of nuisance ionizing sources.

We analyze the configuration of a thin rotating accretion disk, which is embedded in a magnetic field inducing a backreaction in the gravitating plasma. The aim of this study is to determine the conditions under which the gaseous accretion model of Shakura can be reconciled with the magnetohydrodynamical picture requested to trigger the underlying turbulent behavior. We focus our attention on the generalized Ohm equation in order to understand if the plasma backreaction is able to provide the proper toroidal current, allowing a nonzero infalling velocity. In the limit of linear plasma backreaction, this analysis shows how the Shakura profile of accretion turns out to be inconsistent. In particular, comparing the azimuthal and the generalized Ohm equilibrium equations, we argue that it is not possible to maintain a constant rate of accretion. A nonstationary scenario for the disk configuration is then outlined and it results in a transient process which is however associated to a vanishing accretion rate.

We consider the quantum effects of matter fields in scalar-tensor theories and clarify the role of the trace anomaly when switching between conformally related “frames.” We exploit the property that the couplings between the scalar and the gauge fields are not frame-invariant in order to define a “QCD frame,” where the scalar is not coupled to the gluons. We show that this frame is a natural generalization of the “Jordan frame” in the case of nonmetric theories and that it is particularly convenient for gravitational phenomenology: test bodies have trajectories that are as close as possible to geodesics with respect to such a metric and equivalence principle violations are directly proportional to the scalar coupling parameters written in this frame. We show how renormalization group flow and decoupling work in metric and nonmetric theories. Renormalization group running commutes with the operation of switching between frames at different scales. When only matter loops are considered, our analysis confirms that metricity is stable under radiative corrections and shows that approximate metricity is natural in a technical sense.

We propose an economical model to explain the apparent 130 GeV gamma ray peak, found in the Fermi/LAT data, in terms of dark matter (DM) annihilation through a dipole moment interaction. The annihilating dark matter particles represent a subdominant component, with mass density 7–17% of the total DM density; and they only annihilate into $\gamma \gamma$, $\gamma Z$, and $ZZ$, through a magnetic (or electric) dipole moment. Annihilation into other standard model particles is suppressed, due to a DM mass splitting in the magnetic dipole case, or to $p$-wave scattering in the electric dipole case. In either case, the observed signal requires a dipole moment of strength $\mu \sim 2/\mathrm{TeV}$. We argue that composite models are the preferred means of generating such a large dipole moment, and that the magnetic case is more natural than the electric one. We present a simple model involving a scalar and fermionic techniquark of a confining SU(2) gauge symmetry. We point out some generic challenges for getting such a model to work. The new physics leading to a sufficiently large dipole moment is below the TeV scale, indicating that the magnetic moment is not a valid effective operator for LHC physics, and that production of the strongly interacting constituents, followed by techni-hadronization, is a more likely signature than monophoton events. In particular, four-photon events from the decays of bound state pairs are predicted.

We study the mechanism of production of the light scalar mesons in the $D_s^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}\nu$ decays: $D_s^{+}\to s\overline{s}{e}^{+}\nu \to [\sigma (600)+f_0(980)]e^{+}\nu \to {\pi }^{+}{\pi }^{-}{e}^{+}\nu$, and we compare it with the mechanism of production of the light pseudoscalar mesons in the $D_s^{+}\to (\eta /{\eta }^{\prime })e^{+}\nu$ decays: $D_s^{+}\to s\overline{s}{e}^{+}\nu \to (\eta /{\eta }^{\prime })e^{+}\nu$. We show that the $s\overline{s}\to \sigma (600)$ transition is negligibly small in comparison with the $s\overline{s}\to f_0(980)$ one. As for the $f_0(980)$ meson, the intensity of the $s\overline{s}\to f_0(980)$ transition makes near thirty percent from the intensity of the $s\overline{s}\to {\eta }_s$ (${\eta }_s=s\overline{s}$) transition. So, the $D_s^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}\nu$ decay supports the previous conclusions about a dominant role of the four-quark components in the $\sigma (600)$ and $f_0(980)$ mesons.

We study the cosmology of Galileon modified gravity models in the linear perturbation regime. We derive the fully covariant and gauge invariant perturbed field equations using two different methods, which give consistent results, and solve them using a modified version of the CAMB code. We find that, in addition to modifying the background expansion history and therefore shifting the positions of the acoustic peaks in the cosmic microwave background power spectrum, the Galileon field can cluster strongly from early times, and causes the Weyl gravitational potential to grow, rather than decay, at late times. This leaves clear signatures in the low-$l$ cosmic microwave background power spectrum through the modified integrated Sachs-Wolfe effect, strongly enhances the linear growth of matter density perturbations and makes distinctive predictions for other cosmological signals such as weak lensing and the power spectrum of density fluctuations. The quasistatic approximation is shown to work quite well from small to the near-horizon scales. We demonstrate that Galileon models display a rich phenomenology due to the large parameter space and the sensitive dependence of the model predictions on the Galileon parameters. Our results show that some Galileon models are already ruled out by present data and that future higher significance galaxy clustering, integrated Sachs-Wolfe, and lensing measurements will place strong constraints on Galileon gravity.

We discuss decays and productions for the possible molecular states formed by bottom mesons $B$ ($B^{*}$) and $\overline{B}$ (${\overline{B}}^{*}$). The twin resonances found by Belle, $Z_b^{\pm ,0}(10610)$ and $Z_b^{\pm }(10650)$, are such candidates. The spin wave functions of the molecular states are rearranged into those of heavy and light spin degrees of freedom by using the recoupling formulas of angular momentum. By applying the heavy quark symmetry we derive model independent relations among various decay and production rates, which can be tested in experiments.

In the scenario with $Z$-mediated flavor changing neutral current occurring at the tree level due to the addition of a vectorlike isosinglet down-type quark $d^{\prime }$ to the SM particle spectrum, we perform a ${\chi }^2$ fit using the flavor physics data and obtain the best fit value along with errors of the tree level $Z\overline{b}s$ coupling, $U_{sb}$. The fit indicates that the new physics coupling is constrained to be small: we obtain $|U_{sb}|\le 3.40\times {10}^{-4}$ at $3\sigma$. Still, this does allow for the possibility of new physics signals in some of the observables, such as semileptonic $CP$ asymmetry in $B_s$ decays.

New physics thresholds which can modify the diphoton and dilepton Higgs branching ratios significantly may also provide new sources of $CP$ and lepton flavor violation. We find that limits on electric dipole moments impose strong constraints on any $CP$-odd contributions to Higgs diphoton decays unless there are degeneracies in the Higgs sector that enhance $CP$-violating mixing. We exemplify this point in the language of effective operators and in simple UV-complete models with vector-like fermions. In contrast, we find that electric dipole moments and lepton-flavor-violating observables provide less stringent constraints on new thresholds contributing to Higgs dilepton decays.