In the companion paper it is shown that there are six observables in $gg\to t\overline{t}\to (b\overline{b}c)(\overline{b}\ell \overline{\nu })$ that can be used to reveal the presence of new physics (NP) in $t\to b\overline{b}c$. In the present paper we examine the prospects for detecting and identifying such NP at the LHC, in both the short term and long term. To this end, we develop an algorithm for extracting the NP parameters from measurements of the observables. In the short term, depending on what measurements have been made, there are several different ways of detecting the presence of NP. It may even be possible to approximately determine the values of certain NP parameters. In the long term, it is expected that all six observables will be measured. The values of the NP parameters can then be determined reasonably precisely from a fit to these measurements, which will provide good information about the type of NP present in $t\to b\overline{b}c$.

In this paper we study new-physics contributions to the top-quark decay $t\to b\overline{b}c$. We search for ways of detecting such new physics via measurements at the LHC. As top quarks are mainly produced at the LHC in $t\overline{t}$ production via gluon fusion, we analyze the process $gg\to t\overline{t}\to (b\overline{b}c)(\overline{b}\ell \overline{\nu })$. We find six observables that can be used to reveal the presence of new physics in $t\to b\overline{b}c$. Three are invariant mass-squared distributions involving two of the final-state particles in the top decay, and three are angular correlations between the final-state quarks coming from the $t$ decay and the ${\ell }^{-}$ coming from the $\overline{t}$ decay. The angular correlations are related to the $t\overline{t}$ spin correlation.

If dark energy and dark matter interact via exchange of energy and momentum, then this may affect the galaxy power spectrum on large scales. When this happens, it may be degenerate with the signal from primordial non-Gaussianity via a scale-dependent bias. We consider a class of interacting dark energy models and show that the matter overdensity is scale dependent on large scales. We estimate the effective non-Gaussianity arising from the large-scale effects of interaction in the dark sector. The signal of dark sector interaction can be disentangled from a primordial non-Gaussian signal by measuring the power at two redshifts.

k-inflation represents the most general single-field inflation, in which the perturbations usually obey an equation of motion with a time-dependent sound speed. In this paper, we study the observational predictions of the k-inflation by using the high-order uniform asymptotic approximation method. We calculate explicitly the slow-roll expressions of the power spectra, spectral indices, and running of the spectral indices for both the scalar and tensor perturbations. These expressions are all written in terms of the Hubble and sound speed flow parameters. It is shown that the previous results obtained by using the first-order uniform asymptotic approximation have been significantly improved by the high-order corrections of the uniform asymptotic approximations. Furthermore, we also check our results by comparing them with the ones obtained by other approximation methods, including the Green’s function method, WKB approximation, and improved WKB approximation, and find the relative errors.

We discuss leptogenesis constraints on the mass of the right-handed $W$ boson ($W_R$) in a TeV-scale left-right seesaw model for neutrino masses. For generic Dirac mass of the neutrinos, i.e. with all Yukawa couplings $\lesssim 10^{-5.5}$, it has been pointed out that successful leptogenesis requires a lower bound of 18 TeV on the $W_R$ mass, pushing it beyond the reach of the LHC. Such TeV-scale left-right seesaw model must, however, be parity asymmetric for type-I seesaw to give the observed neutrino masses. This class of models can accommodate larger Yukawa couplings, which give simultaneous fits to charged-lepton and neutrino masses, by invoking either cancellations or specific symmetry textures for Dirac ($M_D$) and Majorana ($M_N$) masses in the seesaw formula. We show that in this case the leptogenesis bound on $M_{W_R}$ can be substantially weaker, i.e. $M_{W_R}\gtrsim 3\mathrm{TeV}$ for $M_N\lesssim M_{W_R}$. This happens due to considerable reduction of the dilution effects from $W_R$-mediated decays and scatterings, while the washout effects due to inverse decays are under control for certain parameter ranges of the Yukawa couplings. We also show that this model is consistent with all other low-energy constraints, such as lepton flavor violation and neutrinoless double beta decay. Thus, a discovery of the right-handed gauge bosons alone at the LHC will not falsify leptogenesis as the mechanism behind the matter-antimatter asymmetry in our Universe.

We investigate a neutral gauge boson $X_{\mu }$ that originates from a hidden $U(1)$ extension of the standard model as the particle dark matter candidate. Vector dark matter interacts with the standard model fermions through heavy fermion mediators. The interactions give rise to a $t$-channel annihilation cross section in the $XX\to f\overline{f}$ process, which dominates the thermal relic abundance during thermal freeze-out and produces measurable gamma-ray flux in the galactic halo. For a light vector dark matter, if it predominantly couples to the third-generation fermions, this model could explain the excess of gamma rays from the Galactic Center. We show that vector dark matter with a mass of $\sim 20–40\mathrm{GeV}$ and which annihilates into the $b\overline{b}$ and $\tau \overline{\tau }$ final states provides an excellent description of the observed gamma-ray excess. The parameter space aimed at explaining the gamma-ray excess could also provide the correct thermal relic density and is compatible with the constraints from electroweak precision data, Higgs invisible decay, and collider searches. We show the dark matter couplings to the nucleon from the fermion portal interactions are loop suppressed, and only contribute to the spin-dependent cross section. Therefore vector dark matter could easily escape the stringent constraints from the direct-detection experiments.

Electric conductivity is sensitive to effective cross sections among the particles of the partonic medium. We investigate the electric conductivity of a hot plasma of quarks and gluons, solving the relativistic Boltzmann equation. In order to extract this transport coefficient, we employ the Green-Kubo formalism and, independently, a method motivated by the classical definition of electric conductivity. To this end we evaluate the static electric diffusion current upon the influence of an electric field. Both methods give identical results. For the first time, we obtain numerically the Drude electric conductivity formula for an ultrarelativistic gas of quarks and gluons employing constant isotropic binary cross sections. Furthermore, we extract the electric conductivity for a system of massless quarks and gluons including screened binary and inelastic, radiative $2\leftrightarrow 3$ perturbative QCD scattering. Comparing with recent lattice results, we find an agreement in the temperature dependence of the conductivity.

The newly observed hidden-charm meson $Z_c^{+}(3900)$ with quantum numbers $J^P=1^{+}$ is considered as a hadronic molecule composed of $\overline{D}{D}^{*}$. We give detailed predictions for the decay modes $Z_c^{+}\to J/\psi {\pi }^{+}\gamma$ and $Z_c^{+}\to J/\psi {\pi }^{+}{\ell }^{+}{\ell }^{-}(\ell =e,\mu )$ in a phenomenological Lagrangian approach.

We consider relativistic charged-particle dynamics and relativistic magnetohydrodynamics using symplectic structures and actions given in terms of coadjoint orbits of the Poincaré group. The particle case is meant to clarify some points such as how minimal coupling (as defined in the text) leads to a gyromagnetic ratio $g=2$ and to set the stage for fluid dynamics. The general group-theoretic framework is further explained and is then used to set up Abelian magnetohydrodynamics including spin effects. An interesting new physical effect is precession of spin density induced by gradients in pressure and energy density. The Euler equation (the dynamics of the velocity field) is also modified by gradients of the spin density.

Multiscale renormalization group (RG) methods are reviewed and applied to the analysis of the effective potential for radiative symmetry breaking with multiple scalar fields, allowing an extension of the Gildener and Weinberg method beyond the weak coupling limit. A model containing two interacting real scalar fields is used to illustrate multiscale RG methods and the multiscale RG functions of this model are calculated to one-loop order for the $\beta$ function and two-loop order for the anomalous mass dimension. The introduction of an extra renormalization scale allows the mapping of the effective potential in this model onto a RG-equivalent form with an $O(2)$ symmetric structure along a particular trajectory in the multiple renormalization-scale space, leading to a simplified form of the effective potential. It is demonstrated that the physical content of the effective potential in the original model, referenced to a single conventional renormalization scale, can be extracted from a particular RG trajectory that connects to this multiscale $O(2)$-symmetric form of the effective potential. Extensions of these multiscale methods for effective potentials in models containing multiple scalars with $O(M)\times O(N)$ symmetry are also discussed.

We determine the leading order falloff behavior of the Weyl tensor in higher-dimensional Einstein spacetimes (with and without a cosmological constant) as one approaches infinity along a congruence of null geodesics. The null congruence is assumed to “expand” in all directions near infinity (but it is otherwise generic), which includes in particular asymptotically flat spacetimes. In contrast to the well-known four-dimensional peeling property, the falloff rate of various Weyl components depends substantially on the chosen boundary conditions and is also influenced by the presence of a cosmological constant. The leading component is always algebraically special, but in various cases, it can be of type N, III, or II.

No experiment can measure an absolute scale: every dimensionful quantity has to be compared to some fixed unit scale in order to be measured, and thus only dimensionless quantities are really physical. The Einstein and Jordan frames are related by a conformal transformation of the metric, which amounts to rescaling all length scales. Since the absolute scale cannot be measured, both frames describe the same physics and are equivalent. In this article we make this explicit by rewriting the action in terms of dimensionless variables, which are invariant under a conformal transformation. For definitiveness, we concentrate on the action of Higgs inflation, but the results can easily be generalized. In addition, we show that the action for $f(R)$ gravity, which includes Starobinsky inflation, can be written in a frame-independent form.

We study the effect of sudden transitions in the effective Planck mass during inflation on primordial power spectra. Specifically, we consider models in which this variation results from the nonminimal coupling of a Brans-Dicke type scalar field. We find that the scalar power spectra develop features at the scales corresponding to those leaving the horizon during the transition. In addition, we observe that the tensor perturbations are largely unaffected, so long as the variation of the Planck mass is below the percent level. Otherwise, the tensor power spectra exhibit damped oscillations over the same scales. Due to significant features in the scalar power spectra, the tensor-to-scalar ratio $r$ shows variation over the corresponding scales. Thus, by studying the spectra of both scalar and tensor perturbations, one can constrain sudden but small variations of the Planck mass during inflation. We illustrate these effects with a number of benchmark single- and two-field models. In addition, we comment on their implications and the possibility to alleviate the tension between the observations of the tensor-to-scalar ratio performed by the Planck and BICEP2 experiments.

It is generally believed that the decay mode $B\to K^{*}{\ell }^{+}{\ell }^{-}$ is one of the best modes to search for physics beyond the standard model. The angular distribution enables the independent measurement of several observables as a function of the dilepton invariant mass. The plethora of observables so obtained enable unique tests of the standard model contributions. We start by writing the most general parametric form of the standard model amplitude for $B\to K^{*}{\ell }^{+}{\ell }^{-}$ taking into account comprehensively all contributions within the standard model. These include all short-distance and long-distance effects, factorizable and nonfactorizable contributions, complete electromagnetic corrections to hadronic operators up to all orders, resonance contributions and the finite lepton and quark masses. The parametric form of the amplitude in the standard model results a new relation involving all the $CP$ conserving observables. The derivation of this relation only needs the parametric form of the amplitude and not a detailed calculation of it. Hence, we make no approximations, however, innocuous. The violation of this relation will provide a smoking gun signal of new physics. We use the $1{\mathrm{fb}}^{-1}$ $\mathrm{LHC}b$ data to explicitly show how our relation can be used to test standard model and search for new physics that might contribute to this decay.

We study the impact on leptogenesis of Higgs portal couplings to a new scalar singlet. These couplings open up additional $CP$-violating decay channels for the higher mass singlet neutrinos $N_2$ and $N_3$. We analyze the simplest case of two-level $N_1-N_2$ leptogenesis, including significant mass hierarchies, in which the $CP$ asymmetry is generated in part by singlet-mediated decays of $N_2$. For these models, provided the lightest singlet neutrino $N_1$ is sufficiently weakly coupled to avoid excessive washout, its mass scale is not directly constrained by the Davidson–Ibarra bound.