We present analytical results for top-quark decay processes, in an effective field theory beyond the standard model, at next-to-leading order in QCD. We parametrize new physics effects using dimension-six operators, and consider all operators that give rise to nonstandard interactions of the top quark. We investigate both the flavor-conserving and flavor-changing decay modes, including their two-body and three-body semileptonic final states. The QCD mixing among relevant operators is also taken into account. These results provide all information needed for a complete model-independent study of top-quark decay at next-to-leading order accuracy, paving the way to global analyses for new physics effects in an effective field theory approach.

We present the results of a numerical search for the Dirac Yukawa matrices of the Standard Model, consistent with the quark and lepton masses and their mixing angles. We assume a diagonal up-quark matrix, natural in ${\mathcal{Z}}_{\mathbf{7}}⋊{\mathcal{Z}}_{\mathbf{3}}$, bimaximal or tribimaximal seesaw mixing, and $SU(5)$ unification to relate the down-quark and charged lepton Dirac Yukawa matrices using Georgi-Jarlskog mechanisms. The measured value of ${\theta }_{13}$ requires an asymmetric down-quark Yukawa matrix. Satisfying the measured values of both ${\theta }_{13}$ and the electron mass restricts the number of solutions, underlying the importance of the recent measurement of the reactor angle.

We study the production of heavy Majorana neutrinos ($N$) in $e^{-}\gamma$ colliders. We consider the tree-level process $e^{-}\gamma \to W^{-}N$, which allows for lepton number violation via the decay $N\to l^{+}2j$. We follow the approach of an effective theory, where we consider all possible gauge invariant and nonrenormalizable operators of lowest dimension, which determine the interactions of the Majorana neutrino with the standard particles. We study the total cross section for different masses of the Majorana neutrino and different center-of-mass energies. We give an estimate for the range of the Majorana neutrino masses which may be detected in a $e^{-}\gamma$ collider.

An energy scan near the $\tau$ pair production threshold has been performed using the BESIII detector. About $24{\mathrm{pb}}^{-1}$ of data, distributed over four scan points, were collected. This analysis is based on $\tau$ pair decays to $ee$, $e\mu$, $eh$, $\mu \mu$, $\mu h$, $hh$, $e\rho$, $\mu \rho$ and $\pi \rho$ final states, where $h$ denotes a charged $\pi$ or $K$. The mass of the $\tau$ lepton is measured from a maximum likelihood fit to the $\tau$ pair production cross-section data to be $m_{\tau }=(1776.91\pm {0.12}_{-0.13}^{+0.10})\mathrm{MeV}/c^2$, which is currently the most precise value in a single measurement.

We present a nonparametric form-invariance transformation through which we establish a link between phantom and tachyonic models in flat Friedmann-Robertson-Walker cosmologies.

We use currently available cosmic observations to probe and constrain an imperfect dark-energy fluid that is characterized by a constant equation of state $w$ and a constant speed of viscosity $c_{vis}^2$. The model parameter space was scanned using the Markov chain Monte Carlo method. The results show that the speed of viscosity $c_{vis}^2$ was not well constrained when currently available data sets are used (including the cosmic microwave background radiation from Planck-2013 and WMAP9, type Ia supernovae, baryon acoustic oscillations, redshift space distortion $f{\sigma }_8(z)$, and gravitational weak lensing from Canada-France Hawaii Telescope Lensing Survey (CFHTLenS). However, the cosmic data sets slightly favor phantom dark energy with a negative speed of viscosity $c_{vis}^2$.

We study a model for a nonsingular cosmic bounce in $\mathcal{N}=1$ supergravity, based on supergravity versions of the ghost condensate and cubic Galileon scalar field theories. The bounce is preceded by an ekpyrotic contracting phase, which prevents the growth of anisotropies in the approach to the bounce and allows for the generation of scale-invariant density perturbations that carry over into the expanding phase of the Universe. We present the conditions required for the bounce to be free of ghost excitations, as well as the tunings that are necessary in order for the model to be in agreement with cosmological observations. All of these conditions can be met. Our model thus provides a proof-of-principle that nonsingular bounces are viable in supergravity, despite the fact that during the bounce the null energy condition is violated.

We study the $2+1$ dimensional Abelian Higgs model defined on a spatial torus at critical self-coupling. We propose a method to compute the quantum contribution to the mass of the Abrikosov-Nielsen-Olesen vortex and to multivortex energies. The one-loop quantum correction to multivortex energies is computed analytically at the critical value of the torus area (Bradlow limit). For other values of the area one can set up an expansion around this critical area (Bradlow parameter expansion). The method is explained and the next-to-leading term explicitly evaluated. To this order, the resulting energies depend on the torus periods, but not on the vortex positions.

We study the impact of the zero mode of a quantum field on the evolution of a particle detector. For a massless scalar field in a periodic cavity, we show that the impact of the zero mode on the Unruh-DeWitt detector and its derivative-coupling generalization is necessarily nonvanishing but can be made negligible in some limits, including those commonly occurring in nonrelativistic quantum optics. For the derivative-coupling detector this can be accomplished by just tuning the zero mode’s initial state, but the standard Unruh-DeWitt detector requires a more subtle and careful tuning. Applications include an inertial detector with arbitrary velocity, where we demonstrate the regularity of the ultrarelativistic limit, and a detector with uniform acceleration.

We introduce a new Markov-chain Monte Carlo (MCMC) approach designed for the efficient sampling of highly correlated and multimodal posteriors. Parallel tempering, though effective, is a costly technique for sampling such posteriors. Our approach minimizes the use of parallel tempering, only applying it for a short time to build a proposal distribution that is based upon estimation of the kernel density and tuned to the target posterior. This proposal makes subsequent use of parallel tempering unnecessary, allowing all chains to be cooled to sample the target distribution. Gains in efficiency are found to increase with increasing posterior complexity, ranging from tens of percent in the simplest cases to over a factor of 10 for the more complex cases. Our approach is particularly useful in the context of parameter estimation of gravitational-wave signals measured by ground-based detectors, which is currently done through Bayesian inference with MCMC, one of the leading sampling methods. Posteriors for these signals are typically multimodal with strong nonlinear correlations, making sampling difficult. As we enter the advanced-detector era, improved sensitivities and wider bandwidths will drastically increase the computational cost of analyses, demanding more efficient search algorithms to meet these challenges.

We have investigated the local invariant scalar observables—energy density and flux—which explicitly depend on the kinematics of the concerned observers in the thin null shell gravitational collapse geometry. The use of globally defined null coordinates allows for the definition of a unique in-vacuum for the scalar field propagating in this background. Computing the stress-energy tensor for this scalar field, we work out the energy density and flux for the static observers outside the horizon and then consider the radially in-falling observers who fall in from some specified initial radius all the way through the horizon and inside to the eventual singularity. Our results confirm the thermal Tolman-shifted energy density and fluxes for the static observers which diverge at the horizon. For the in-falling observer starting from far off, both the quantities—energy density and flux—at the horizon crossing are regular and finite. For example, the flux at the horizon for the in-falling observer from infinity is approximately 24 times the flux for the observer at infinity. Compared with the static observers in the near-horizon region, this is quite small. Both the quantities grow as the in-fall progresses inside the horizon and diverge at the singularity.

We discuss LHC phenomenologies of the top-mode pseudo-Nambu-Goldstone bosons (pNGBs)$(h_t^0,A_t^0)$, composite pNGBs predicted in the model recently proposed in a framework of the top-quark condensation. The CP-even top-mode pNGB, dubbed tHiggs ($h_t^0$), is identified with the 126 GeV Higgs boson at the LHC. We analyze the coupling properties of the tHiggs in comparison with the currently available data reported from LHC Run-I to find that the tHiggs can be consistent with the LHC Higgs boson. The mass formula relating masses of the top-mode pNGBs allows us to place an indirect limit on the mass of the CP-odd top-mode pNGBs ($A_t^0$) from the constraint on the tHiggs coupling strengths. The presence of the mass formula also significantly affects the coupling property of $A_t^0$, which ensures $A_t^0$ weakly coupled to the Standard Model particles. The direct limit on the mass of $A_t^0$ is placed by data on searches for new resonances in several channels at the LHC Run-I. We find the lower mass bound from both the indirect and direct limits, $m_{A_t^0}\gtrsim 560\mathrm{GeV}$. The discovery channel of $A_t^0$ in the upcoming LHC Run-II is also addressed.

We suggest that the Higgs boson is a light composite state that does not emerge from TeV scale strong dynamics for any generic reason, such as when it is pseudo-Goldstone boson. Instead, a state that is Higgs-like and fairly decoupled from heavier states may simply be a reflection of very particular strong dynamics, with properties quite distinct from more familiar large-$N_c$ type gauge dynamics. We elaborate on this picture in the context of a strongly interacting fourth family and an effective 4-Higgs-doublet model. The origin of a decoupling limit and the corrections to it are discussed.

In this work, we use the results from Higgs searches in the $\gamma \gamma$ and $\tau \tau$ decay channels at LHC and indirect bounds as $\mathrm{BR}(B\to X_s\gamma )$ to constrain the parameter space of a generic minimal supersymmetric standard model (MSSM) Higgs sector. In particular, we include the latest CMS results that look for additional Higgs states with masses up to 1 TeV. We show that the $\tau \tau$ channel is the best and most accurate tool in the hunt for new Higgs states beyond the standard model. We obtain that present experimental results rule out additional neutral Higgs bosons in a generic MSSM below 300 GeV for any value of $\tan \beta$ and, for instance, values of $\tan \beta$ above 30 are only possible for Higgs masses above 600 GeV. ATLAS stored data have the potential to render this bound obsolete in the near future.

We present the first unquenched lattice QCD results for the bag parameters controlling the short distance contribution to $D$ meson oscillations in the standard model and beyond. We have used the gauge configurations produced by the European Twisted Mass collaboration with $N_f=2$ dynamical quarks, at four lattice spacings and light meson masses in the range 280–500 MeV. Renormalization is carried out nonperturbatively with the regularization-independent momentum subtraction method. The bag-parameter results have been used to constrain new physics effects in $D^0-{\overline{D}}^0$ mixing, to put a lower bound to the generic new physics scale and to constrain off-diagonal squark mass terms for TeV-scale supersymmetry.

To avoid possible electroweak vacuum instability in the vectorlike fermion model, we introduce a new singlet scalar to the model, which couples to the vectorlike fermion and also mixes with the Higgs boson after spontaneous symmetry breaking. We investigate the vectorlike fermion predominantly coupled to the third-generation quarks, and its mass is generated from the vacuum expectation value of the new scalar field in the model. In this setup, as running towards high energies, the new scalar provides a positive contribution to the running of the Higgs quartic coupling, and the matching on the scale of the scalar mass gives rise to a threshold effect that lifts up the Higgs quartic coupling strength. The two effects help stabilize the electroweak vacuum of the Higgs potential. Therefore, this setup could evade possible vacuum instability in the vectorlike fermion model. We show that a large range of parameter space is allowed to have both stable Higgs vacuum and perturbativity of all the running couplings, up to the Planck scale. We also examine the experimental constraints from the electroweak precision observables such as oblique corrections $S,T$ and nonoblique corrections to the $Z{b}_L{\overline{b}}_L$ coupling, the Higgs coupling precision measurements, and the current LHC direct searches.

We study nonradial oscillations of neutron stars with superfluid baryons, in a general relativistic framework, including finite temperature effects. Using a perturbative approach, we derive the equations describing stellar oscillations, which we solve by numerical integration, employing different models of nucleon superfluidity, and determining frequencies and gravitational damping times of the quasinormal modes. As expected by previous results, we find two classes of modes, associated to superfluid and non-superfluid degrees of freedom, respectively. We study the temperature dependence of the modes, finding that at specific values of the temperature, the frequencies of the two classes of quasinormal modes show avoided crossings, and their damping times become comparable. We also show that, when the temperature is not close to the avoided crossings, the frequencies of the modes can be accurately computed by neglecting the coupling between normal and superfluid degrees of freedom. Our results have potential implications on the gravitational wave emission from neutron stars.

We study general metric-affine theories of gravity in which the metric and connection are the two independent fundamental variables. In this framework, we use Lagrange–Noether methods to derive the identities and the conservation laws that correspond to the invariance of the action under general coordinate transformations. The results obtained are applied to generalized models with nonminimal coupling of matter and gravity, with a coupling function that depends arbitrarily on the covariant gravitational field variables.

In the context of dark energy solutions, we consider a Friedmann—Robertson—Walker spacetime filled with a noninteracting mixture of dust and a viscous fluid, for which the bulk viscosity is governed by the nonlinear model proposed in [R. Maartens and V. Méndez, Phys. Rev. D 55, 1937 (1997)]. Through a phase-space analysis of the equivalent dynamical system, the existence and stability of critical solutions are established, and the respective scale factors are computed. The results point toward the possibility of describing the current accelerated expansion of the Universe by means of the above-mentioned nonlinear model for viscosity.