Two-body charmless hadronic $B_c$ decays involving a light $1{{}^{3}P}_2$-tensor ($T$) meson are investigated for the first time within the framework of perturbative QCD (pQCD) at leading order, in which the other meson is the lightest pseudoscalar ($P$) or vector ($V$) state. The concerned processes can only occur through the pure weak annihilation topology in the standard model. We predict the $CP$-averaged branching ratios and polarization fractions of those considered decays in Cabibbo-Kobayashi-Maskawa (CKM) favored and suppressed modes. Phenomenologically, several modes—such as the $B_c\to K_2^{*}(1430)K$ and the CKM-favored $B_c\to TV$—have large decay rates of ${10}^{-6}$, which are expected to be detected at Large Hadron Collider experiments in the near future. Moreover, all of the $B_c\to TV$ modes are governed by the longitudinal amplitudes in the pQCD calculations and the corresponding fractions vary around 78–98%. A confirmation of these results could prove the reliability of the pQCD approach used here and further shed some light on the annihilation decay mechanism.

Taking into account the current global information on neutrino oscillation parameters we forecast the capabilities of future long-baseline experiments such as DUNE and T2HK in settling the atmospheric octant puzzle. We find that a good measurement of the reactor angle ${\theta }_{13}$ plays a key role in fixing the octant of the atmospheric angle ${\theta }_{23}$ with such future accelerator neutrino studies.

In this paper, we study canonical scalar field models, with a varying second slow-roll parameter, that allow transitions between constant-roll eras. In the models with two constant-roll eras, it is possible to avoid fine-tunings in the initial conditions of the scalar field. We mainly focus on the stability of the resulting solutions, and we also investigate if these solutions are attractors of the cosmological system. We shall calculate the resulting scalar potential and, by using a numerical approach, we examine the stability and attractor properties of the solutions. As we show, the first constant-roll era is dynamically unstable towards linear perturbations, and the cosmological system is driven by the attractor solution to the final constant-roll era. As we demonstrate, it is possible to have a nearly scale-invariant power spectrum of primordial curvature perturbations in some cases; however, this is strongly model dependent and depends on the rate of the final constant-roll era. Finally, we present, in brief, the essential features of a model that allows oscillations between constant-roll eras.

Dynamical dark energy has been recently suggested as a promising and physical way to solve the 3 sigma tension on the value of the Hubble constant $H_0$ between the direct measurement of Riess et al. (2016) (R16, hereafter) and the indirect constraint from cosmic microwave anisotropies obtained by the Planck satellite under the assumption of a $\mathrm{\Lambda }\mathrm{CDM}$ model. In this paper, by parametrizing dark energy evolution using the $w_0-w_a$ approach, and considering a 12 parameter extended scenario, we find that: (a) the tension on the Hubble constant can indeed be solved with dynamical dark energy, (b) a cosmological constant is ruled out at more than 95% c.l. by the $\mathrm{Planck}+\mathrm{R}16$ dataset, and (c) all of the standard quintessence and half of the “downward going” dark energy model space (characterized by an equation of state that decreases with time) is also excluded at more than 95% c.l. These results are further confirmed when cosmic shear, CMB lensing, or SN Ia luminosity distance data are also included. The best fit value of the ${\chi }^2$ for the $\mathrm{Planck}+\mathrm{R}16$ data set improves by $\mathrm{\Delta }{\chi }^2=-12.9$ when moving to 12 parameters respect to standard $\mathrm{\Lambda }\mathrm{CDM}$. However, tension remains with the BAO dataset. A cosmological constant and small portion of the freezing quintessence models are still in agreement with the $\mathrm{Planck}+\mathrm{R}16+\mathrm{BAO}$ data set at between 68% and 95% c.l. Conversely, for Planck plus a phenomenological $H_0$ prior, both thawing and freezing quintessence models prefer a Hubble constant of less than $70\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$. The general conclusions hold also when considering models with nonzero spatial curvature.

We revisit the physical properties of global and local monopoles and discuss their implications in the dynamics of monopole networks. In particular, we review the velocity-dependent one-scale (VOS) model for global and local monopoles and propose physically motivated changes to its equations. We suggest a new form for the acceleration term of the evolution equation of the root-mean-squared velocity and show that, with this change, the VOS model is able to describe the results of radiation and matter era numerical simulations of global monopole networks with a single value of the acceleration parameter $k$, thus resolving the tension previously found in the literature. We also show that the fact that the energy of global monopoles is not localized within their cores affects their dynamics and thus the Hubble damping terms in the VOS equations. We study the ultrarelativistic linear scaling regime predicted by the VOS equations and demonstrate that it cannot be attained either on radiation or matter eras and thus cannot arise from the cosmological evolution of a global monopole network. We also briefly discuss the implications of our findings for the VOS model for local monopoles.

We give a scalar field description of two dark energy parametrizations, and we analyze in detail its cosmology both at the level of background evolution and at the level of linear perturbations. In particular, we compute the statefinder parameters and the growth index as functions of the redshift for both dark energy parametrizations, and the comparison with the $\mathrm{\Lambda }\mathrm{CDM}$ model as well as with a few well-known geometrical dark energy models is shown. In addition, the combination parameter $A=f{\sigma }_8$ of both models is compared against current data.

In this paper, we consider vacuum polarization effects in the model of charged fermions with anomalous magnetic moment and axial-vector interaction term in a constant and uniform magnetic field. Nontrivial corrections to the effective Lagrangian from the anomalous moment and axial-vector term are calculated with account for various configurations of parameters of the model. An analogue of the chiral magnetic effect in the axial-vector background as well as a vacuum current induced under the combined action of the anomalous magnetic moment of fermions and the axial vector background in a magnetic field is also calculated.

Motivated by the flavored Peccei-Quinn symmetry for unifying the flavor physics and string theory, we construct an explicit model by introducing a $U(1)$ symmetry such that the $U(1{)}_X-[\text{gravity}{]}^2$ anomaly-free condition together with the standard model flavor structure demands additional sterile neutrinos as well as no axionic domain-wall problem. Such additional sterile neutrinos play the role of realizing baryogenesis via a new Affleck-Dine leptogenesis. We provide grounds for interpreting the $U(1{)}_X$ symmetry as a fundamental symmetry of nature. The model will resolve rather recent but fast-growing issues in astroparticle physics, including leptonic mixings and $CP$ violation in neutrino oscillation, high-energy neutrinos, QCD axions, and axion cooling of stars. The QCD axion decay constant, through its connection to the astrophysical constraints of stellar evolution and the SM fermion masses, is shown to be fixed at $F_A={1.30}_{-0.54}^{+0.66}\times 10^9\mathrm{GeV}$ (consequently, its mass is $m_a=4.34_{-1.49}^{+3.37}\mathrm{meV}$ and the axion-photon coupling is $|g_{a\gamma \gamma }|={1.30}_{-0.45}^{+1.01}\times {10}^{-12}{\mathrm{GeV}}^{-1}$). Interestingly enough, we show that neutrino oscillations at low energies could be connected to astronomical-scale baseline neutrino oscillations. The model predicts the nonobservational neutrinoless double beta ($0\nu \beta \beta$) decay rate as well as a remarkable pattern between the leptonic Dirac $CP$ phase (${\delta }_{CP}$) and the atmospheric mixing angle (${\theta }_{23}$); e.g., ${\delta }_{CP}\simeq 220°–240°$, 120°–140° for ${\theta }_{23}=42.3°$ for normal mass ordering, and ${\delta }_{CP}\simeq 283°$, 250°, 100°, 70° for ${\theta }_{23}=49.5°$ for the inverted one. We stress that future measurements on the ${\theta }_{23}$, $0\nu \beta \beta$ decay rate, the sum of active neutrino masses, the track-to-shower ratio of a cosmic neutrino, astrophysical constraints on axions, QCD axion mass, and the axion-photon coupling are of importance to test the model in the near future.

In this paper, we explore the discriminatory power of the matrix element method (MEM) in constraining the $L_{\mu }-L_{\tau }$ model at the LHC. The $Z^{\prime }$ boson associated with the spontaneously broken $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetry only interacts with the second and third generation of leptons at tree level, and is thus difficult to produce at the LHC. We argue that the best channels for discovering this $Z^{\prime }$ are in $Z\to 4\mu$ and $2\mu +{\cancel{E}}_T$. Both these channels have a large number of kinematic observables, which strongly motivates the usage of a multivariate technique. The MEM is a multivariate analysis that uses the squared matrix element $|\mathcal{M}{|}^2$ to quantify the likelihood of the testing hypotheses. As the computation of the $|\mathcal{M}{|}^2$ requires knowing the initial and final state momenta and the model parameters, it is not commonly used in new physics searches. Conventionally, new parameters are estimated by maximizing the likelihood of the signal with respect to the background, and we outline scenarios in which this procedure is (in)effective. We illustrate that the new parameters can also be estimated by studying the $|\mathcal{M}{|}^2$ distributions, and, even if our parameter estimation is off, we can gain better sensitivity than cut-and-count methods. Additionally, unlike the conventional MEM, where one integrates over all unknown momenta in processes with ${\cancel{E}}_T$, we show an example scenario where these momenta can be estimated using the process topology. This procedure, which we refer to as the “modified squared matrix element,” is computationally much faster than the canonical matrix element method and maintains signal-background discrimination. Bringing the MEM and the aforementioned modifications to bear on the $L_{\mu }-L_{\tau }$ model, we find that with $300{\mathrm{fb}}^{-1}$ of integrated luminosity, we are sensitive to the couplings of $g_{Z^{\prime }}\gtrsim 0.002g_1$ and $M_{Z^{\prime }}<20\mathrm{GeV}$, and $g_{Z^{\prime }}\gtrsim 0.005g_1$ and $20\mathrm{GeV}<M_{Z^{\prime }}<40\mathrm{GeV}$, which is about an order of magnitude improvement over the cut-and-count method for the same amount of data.

We study the phenomenological implications of the presence of two texture zeros in the neutrino mass matrix assuming that the neutrino mixing matrix has its first column identical to that of the tribimaximal mixing matrix. Only two patterns of this kind are compatible with the experimental data. These textures have definite predictions for the neutrino observables that are testable in future neutrino experiments.

The radion scalar field might be the lightest new particle predicted by extradimensional extensions of the standard model. It could thus lead to the first signatures of new physics at the LHC collider. We perform a complete study of the radion production in association with the Z gauge boson in the custodially protected warped model with a brane-localized Higgs boson addressing the gauge hierarchy problem. Radion-Higgs mixing effects are present. Such a radion production receives possibly resonant contributions from the Kaluza-Klein excitations of the Z boson as well as the extra neutral gauge boson (Z’). All the exchange and mixing effects induced by those heavy bosons are taken into account in the radion coupling and rate calculations. The investigation of the considered radion production at the LHC allows us to be sensitive to some parts of the parameter space but only the ILC program at high luminosity would cover most of the theoretically allowed parameter space via the studied reaction. Complementary tests of the same theoretical parameters can be realized through the high accuracy measurements of the Higgs couplings at the ILC. The generic sensitivity limits on the rates discussed for the LHC and ILC potential reach can be applied to the searches for other (light) exotic scalar bosons.

A symmetry-preserving treatment of a vector-vector contact interaction is used to study charmed heavy-light mesons. The contact interaction is a representation of nonperturbative kernels used in Dyson-Schwinger and Bethe-Salpeter equations of QCD. The Dyson-Schwinger equation is solved for the $u$, $d$, $s$ and $c$ quark propagators and the bound-state Bethe-Salpeter amplitudes respecting spacetime-translation invariance and the Ward-Green-Takahashi identities associated with global symmetries of QCD are obtained to calculate masses and electroweak decay constants of the pseudoscalar $\pi$, $K$, $D$ and $D_s$ and vector $\rho$, $K^{*}$, $D^{*}$, and $D_s^{*}$ mesons. The predictions of the model are in good agreement with available experimental and lattice QCD data.

We calculate the masses and weak decay constants of flavorless and flavored ground and radially excited $J^P=1^{-}$ mesons within a Poincaré covariant continuum framework based on the Bethe-Salpeter equation. We use in both the quark’s gap equation and the meson bound-state equation an infrared massive and finite interaction in the leading symmetry-preserving truncation. While our numerical results are in rather good agreement with experimental values where they are available, no single parametrization of the QCD inspired interaction reproduces simultaneously the ground and excited mass spectrum, which confirms earlier work on pseudoscalar mesons. This feature being a consequence of the lowest truncation, we pin down the range and strength of the interaction in both cases to identify common qualitative features that may help to tune future interaction models beyond the rainbow-ladder approximation.

The $B^{+}\to {D^{*}}^{-}{K}^{+}{\pi }^{+}$ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. A clear signal is observed, and the ratio of its branching fraction to that of the $B^{+}\to D^{*-}{\pi }^{+}{\pi }^{+}$ normalization channel is measured to be $\mathcal{B}(B^{+}\to D^{*-}{K}^{+}{\pi }^{+})/\mathcal{B}(B^{+}\to D^{*-}{\pi }^{+}{\pi }^{+})=(6.39\pm 0.27\pm 0.48)\times {10}^{-2},$ where the first uncertainty is statistical and the second is systematic. This is the first observation of the $B^{+}\to {D^{*}}^{-}{K}^{+}{\pi }^{+}$ decay.

In recent years, the characteristic formulation of numerical relativity has found increasing use in the extraction of gravitational radiation from numerically generated spacetimes. In this paper, we formulate the characteristic initial value problem for $f(R)$ gravity. We consider, in particular, the vacuum field equations of Metric $f(R)$ gravity in the Jordan frame, without utilizing the dynamical equivalence with scalar-tensor theories. We present the full hierarchy of nonlinear hypersurface and evolution equations necessary for numerical implementation in both tensorial and eth forms. Furthermore, we specialize the resulting equations to situations where the spacetime is almost Minkowski and almost Schwarszchild using standard linearization techniques. We obtain analytic solutions for the dominant $\ell =2$ mode and show that they satisfy the concomitant constraints. These results are ideally suited as testbed solutions for numerical codes. Finally, we point out that the characteristic formulation can be used as a complementary analytic tool to the $1+1+2$ semitetrad formulation.

We have recently presented a manifestly local and general coordinate invariant formulation of a nonlocal approach to the cosmological constant problem which has been proposed by Carroll and Remmen. In this article, based on our formulation, we investigate some quantum aspects of this approach to the cosmological constant problem. In particular, we explicitly evaluate quantum effects to the effective cosmological constant from matter fields at one-loop level. We show that the effective cosmological constant receives radiative corrections and is not stable against quantum corrections so that it must be fine-tuned at every stage in the loop expansion. Next, we propose a new geometrical model of a nonlocal approach to the cosmological constant problem, and we show explicitly that in this new model the effective cosmological constant is indeed stable against radiative corrections.

Consider a graph having quantum systems lying at each node. Suppose that the whole thing evolves in discrete time steps, according to a global, unitary causal operator. By causal we mean that information can only propagate at a bounded speed, with respect to the distance given by the graph. Suppose, moreover, that the graph itself is subject to the evolution, and may be driven to be in a quantum superposition of graphs—in accordance to the superposition principle. We show that these unitary causal operators must decompose as a finite-depth circuit of local unitary gates. This unifies a result on quantum cellular automata with another on reversible causal graph dynamics. Along the way we formalize a notion of causality which is valid in the context of quantum superpositions of time-varying graphs, and has a number of good properties. We discuss some of the implications for quantum gravity.

We elucidate the importance of the consistent treatment of gravity-model specific nonlinearities when estimating the growth of cosmological structures from redshift space distortions (RSD). Within the context of standard perturbation theory (SPT), we compare the predictions of two theoretical templates with redshift space data from COLA (comoving Lagrangian acceleration) simulations in the normal branch of DGP gravity (nDGP) and general relativity (GR). Using COLA for these comparisons is validated using a suite of full N-body simulations for the same theories. The two theoretical templates correspond to the standard general relativistic perturbation equations and those same equations modeled within nDGP. Gravitational clustering nonlinear effects are accounted for by modeling the power spectrum up to one-loop order and redshift space clustering anisotropy is modeled using the Taruya, Nishimichi and Saito (TNS) RSD model. Using this approach, we attempt to recover the simulation’s fiducial logarithmic growth parameter $f$. By assigning the simulation data with errors representing an idealized survey with a volume of $10{\mathrm{Gpc}}^3/h^3$, we find the GR template is unable to recover fiducial $f$ to within $1\sigma$ at $z=1$ when we match the data up to $k_{\max }=0.195h/\mathrm{Mpc}$. On the other hand, the DGP template recovers the fiducial value within $1\sigma$. Further, we conduct the same analysis for sets of mock data generated for generalized models of modified gravity using SPT, where again we analyze the GR template’s ability to recover the fiducial value. We find that for models with enhanced gravitational nonlinearity, the theoretical bias of the GR template becomes significant for stage IV surveys. Thus, we show that for the future large data volume galaxy surveys, the self-consistent modeling of non-GR gravity scenarios will be crucial in constraining theory parameters.