We study the exclusive nonleptonic $B_c\to VV$ decays, within the factorization approximation, in the framework of the relativistic independent quark model, based on a confining potential in the scalar-vector harmonic form. The weak form factors are extracted from the overlap integral of meson wave functions derived in the relativistic independent quark model. The predicted branching ratios for different $B_c$-meson decays are obtained in a wide range, from a tiny value of $\mathcal{O}({10}^{-6})$ for $B_c\to D^{*}{D}_{(s)}^{*}$ to a large value of 24.32% for $B_c\to B_s^{*}{\rho }^{-}$, in general agreement with other dynamical-quark-model predictions. The decay modes $B_c\to B_s^{*}{\rho }^{-}$ and $B_c\to B^{*}{\rho }^{-}$ with high branching ratios of 24.32% and 1.73%, respectively, obtained in this model should be detectable at the LHC and Tevatron in the near future. The $b\to c$, $u$ induced decays are predicted predominantly in the longitudinal mode, whereas the $\overline{c}\to \overline{s}$, $\overline{d}$ induced decays are obtained in a slightly higher transverse mode. The $CP$-odd fractions $(R_{\perp })$ for different decay modes are predicted and those for color-favored $B_c\to D^{*}{D}^{*}$, $D^{*}{D}_s^{*}$ decays indicate significant $CP$ violation in this sector.

We study the impact of decoherence on $B$ meson systems with specific emphasis on $B_s$. For consistency we also study the $B_d$ mesons based on the most recent data. Even though the study of decoherence made here depends upon the basis chosen and the final decay products, our analysis suggests that the coherence property of $B$ meson systems is robust and could be a good candidate for making a study of foundational aspects of quantum mechanics.

Lepton mixing can originate from the breaking of a flavor symmetry in different ways in the neutrino and the charged lepton sector. We propose an extension of this framework that allows us to connect the mixing parameters with masses and, more precisely, with certain types of degeneracy of the neutrino mass spectrum. We obtain relations between the mixing parameters for the cases of partial degeneracy, $m_1=m_2$, and complete degeneracy, $m_1=m_2=m_3$. These relations determine also the Majorana phases. It is shown that relatively small corrections to these lowest-order results can produce the required mass splitting and modify the mixing without significant changes of the other symmetry results.

We evaluate the potential of a dedicated search for $t\overline{t}h$ production in the $\mathrm{SSDL}+2b$ channel. Such a measurement provides direct access to the top Yukawa coupling, since the sensitivity is not convolved with the loop-level $h\gamma \gamma$ as is the case for present $t\overline{t}h$ searches. Furthermore, susceptibility to uncertainties in the Higgs width can be reduced by considering a ratio of $\mathrm{SSDL}+2b$ rates with those of the performed $Wh\to WW{W}^{*}$ measurement. The SSDL channel can therefore rely primarily on the already well-measured $h\to W{W}^{*}$ decay. This feasibility study required the development of a new calculation method for “fake” leptons, which constitute the dominant background to our search. Combining measurements from LHC7, LHC8, and in the future LHC14 for the Higgs coupling fit would help resolve any remaining ambiguity between the top Yukawa coupling and a beyond standard model contribution to the $hgg$ coupling.

We consider the collision of two particles in the vicinity of the extremal acceleration horizon (charged or rotating) that includes the Bertotti–Robinson space-time and the geometry of the Kerr throat. It is shown that the energy in the center-of-mass frame $E_{\mathrm{c}.\mathrm{m}.}$ can become indefinitely large if parameters of one of the particles are fine-tuned, so the Bañados–Silk–West (BSW) effect manifests itself. There exists coordinate transformation, which brings the metric into the form free of the horizon. This leads to some paradox since (i) the BSW effect exists due to the horizon and (ii) $E_{\mathrm{c}.\mathrm{m}.}$ is a scalar and cannot depend on the frame. A careful comparison of near-horizon trajectories in both frames enables us to resolve this paradox. Although globally the space-time structure of the metrics with acceleration horizons and black holes are completely different, locally the vicinity of the extremal black hole horizon can be approximated by the metric of the acceleration one. The energy of one particle from the viewpoint of the Kruskal observer (or the one obtained from it by finite local boost) diverges, although in the stationary frame, energies of both colliding particles are finite. This suggests a new explanation of the BSW effect for black holes given from the viewpoint of an observer who crosses the horizon. It is complementary to the previously found explanation from the point of view of a static or stationary observer.

We study the effect of a static homogeneous external magnetic field on charmonium and bottomonium states. In an external magnetic field, quarkonium states do not have a conserved center-of-mass momentum. Instead there is a new conserved quantity called the pseudomomentum which takes into account the Lorentz force on the particles in the system. When written in terms of the pseudomomentum, the internal and center-of-mass motions do not decouple and, as a result, the properties of quarkonia depend on the states’ center-of-mass momentum. We analyze the behavior of heavy particle-antiparticle pairs subject to an external magnetic field assuming a three-dimensional harmonic potential and Cornell potential plus spin-spin interaction. In the case of the Cornell potential, we also take into account the mixing of the ${\eta }_c$ and $J/\psi$ states and ${\eta }_b$ and ${\rm Y}$ states due to the background magnetic field. We then numerically calculate the dependence of the masses and mixing fractions on the magnitude of the background magnetic field and center-of-mass momentum of the state.

We present a simple AdS/QCD model in which the formation of the chiral condensate is dynamically determined. The gauge dynamics is input through the running of the quark bilinear’s anomalous dimension, $\gamma$. The condensate provides a dynamically generated infrared wall in the computation of mesonic bound state masses and decay constants. As an example, we use the model, with perturbative computations of the running of $\gamma$, to study SU(3) gauge theory with a continuous number of quark flavors, $N_f$. We follow the behavior of the spectrum as we approach the conformal window through a walking gauge theory regime. We show such walking theories display a Berezinskii–Kosterlitz–Thoules phase transition, with Miransky scaling, as one approaches the edge of the conformal window at the critical value of $N_f$. We show that these walking theories possess an enhanced quark condensate, a light Higgs-like excitation, and argue that the nonperturbative contribution to S falls to zero. We also study the deformation of the Berezinskii–Kosterlitz–Thoules transition when the quarks have a current mass, which may be of use for understanding lattice simulations of walking theories.

The approximate stress-energy tensor of the quantized massive scalar, spinor, and vector fields in the spatially flat Friedman-Robertson-Walker universe is constructed. It is shown that for the scalar fields with arbitrary curvature coupling, $\xi$, the stress-energy tensor calculated within the framework of the Schwinger-DeWitt approach is identical to the analogous tensor constructed in the adiabatic vacuum. Similarly, the Schwinger-DeWitt stress-energy tensor for the fields of spin $1/2$ and 1 coincides with the analogous result calculated by the Zeldovich-Starobinsky method. The stress-energy tensors thus obtained are subsequently used in the backreaction problem. It is shown that for pure semiclassical Einstein field equations with the vanishing cosmological constant and the source term consisting exclusively of its quantum part, there are no self-consistent exponential solutions driven by the spinor and vector fields. A similar situation takes place for the scalar field if the coupling constant belongs to the interval $\xi \gtrsim 0.1$. For a positive cosmological constant, the expansion slows down for all considered types of massive fields except for minimally coupled scalar field. The perturbative approach to the problem is briefly discussed and possible generalizations of the stress-energy tensor are indicated.

We study the effect of the supersonic relative velocity between dark matter and baryons on large-scale galaxy clustering and derive the constraint on the relative velocity bias parameter from the Baryonic Oscillation Spectroscopic Survey (BOSS) power spectrum measurements. Recent work has shown that the relative velocity effect may have a dramatic impact on the star formation at high redshifts, if first stars are formed in minihalos around $z\sim 20$, or if the effect propagates through secondary effects to stars formed at later redshifts. The relative velocity effect has particularly strong signatures in the large scale clustering of these sources, including the baryonic acoustic oscillation position. Assuming that a small fraction of stars in low-redshift massive galaxies retain the memory of the primordial relative velocity effect, galaxy clustering measurements can be used to constrain the signatures of the first stars. Luminous red galaxies contain some of the oldest stars in the Universe and are ideally suited to search for this effect. Using the BOSS power spectrum measurements from the Sloan Data Release 9, in combination with Planck, we derive the upper limit on the fraction of the stars sensitive to the relative velocity effect $f_{\star }<3.3\%$ at the 95% confidence level in the CMASS galaxy sample. If an additional galaxy sample not sensitive to the effect is available in a given survey, a joint multitracer analysis can be applied to construct a sample-variance canceling combination, providing a model-independent way to verify the presence of the relative velocity effect in the galaxy power spectrum on large scales. Such a multitracer analysis in future galaxy surveys can greatly improve the current constraint, achieving a 0.1% level in $f_{\star }$.

The cosmological Friedmann equation sourced by the trace anomaly of a conformal field theory that is dual to the five-dimensional Schwarzschild-AdS geometry can be derived from the first law of thermodynamics if the apparent horizon of the boundary spacetime acquires a logarithmically corrected Bekenstein-Hawking entropy. It is shown that such a correction to the entropy can arise when the generalized uncertainty principle (GUP) is invoked. The necessary condition for such a thermodynamic derivation directly relates the GUP parameter to the conformal anomaly. It is consistent with the existence of a gravitational cutoff at a scale $l_{\mathrm{uv}}\gtrsim \sqrt{n}{l}_4$ for a theory containing $n$ light species. The absolute minimum in position uncertainty can be identified with the scale at which gravity becomes effectively five dimensional.

We investigate spontaneous global symmetry breaking in the absence of Lorentz invariance and study technical naturalness of Nambu-Goldstone modes for which the dispersion relation exhibits a hierarchy of multicritical phenomena with Lifshitz scaling and dynamical exponents $z>1$. For example, we find Nambu-Goldstone modes with a technically natural quadratic dispersion relation which do not break time reversal symmetry and are associated with a single broken symmetry generator, not a pair. The mechanism is protected by an enhanced “polynomial shift” symmetry in the free-field limit.

Temperature anisotropy of the cosmic microwave background offers a test of the fundamental symmetry of spacetime during cosmic inflation. Violation of rotational symmetry yields a distinct signature in the power spectrum of primordial fluctuations as $P(\mathbf{k})=P_0(k)[1+g_{*}(\widehat{\mathbf{k}}·{\widehat{\mathbf{E}}}_{\mathrm{cl}}{)}^2]$, where ${\widehat{\mathbf{E}}}_{\mathrm{cl}}$ is a preferred direction in space and $g_{*}$ is an amplitude. Using the Planck 2013 temperature maps, we find no evidence for violation of rotational symmetry, $g_{*}=0.002\pm 0.016$ (68% C.L.), once the known effects of asymmetry of the Planck beams and Galactic foreground emission are removed. (Based on observations obtained with the Planck Collaboration, a ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada.)

The electroweak phase transition is considered in the framework of the reduced minimal 3-3-1 model. The structure of the phase transition in this model is divided into two parts. The first part is the phase transition $\mathrm{SU}(3)\to \mathrm{SU}(2)$ at the TeV scale, and the second is $\mathrm{SU}(2)\to \mathrm{U}(1)$, which is like the standard model electroweak phase transition. When the mass of the neutral Higgs boson ($h_1$) is taken to be equal to the LHC value, $m_{h_1}=125\mathrm{GeV}$, these phase transitions are first-order transitions; the mass of $Z_2$ is about 4.8 TeV, and we find the region of parameter space with the first-order phase transition at the $v_{{\rho }_0}=246\mathrm{GeV}$ scale, leading to an effective potential where the mass of the charged Higgs boson is in the range $3.258\mathrm{TeV}<m_{h_{++}}<19.549\mathrm{TeV}$. Therefore, with this approach new bosons are the triggers of the first-order electroweak phase transition, which provides significant implications for the viability of electroweak baryogenesis scenarios.

The first AMS-02 measurement confirms the existence of an excess in the cosmic-ray positron fraction previously reported by the PAMELA and Fermi-LAT experiments. If interpreted in terms of thermal dark matter (DM) annihilation, the AMS-02 result still suggests that the DM annihilation cross section in the present day should be significantly larger than that at freeze-out. The Sommerfeld enhancement of the DM annihilation cross section is a possible explanation, which is however subject to the constraints from DM thermal relic density, mainly due to the annihilation of DM particles into force-carrier particles introduced by the mechanism. We show that the effects of the Sommerfeld enhancement and the relic density constraints depend significantly on the nature of the force carrier. Three scenarios where the force carrier is a vector boson, scalar, and pseudoscalar particle are investigated and compared. The results show that for the case with a vector force carrier, the Sommerfeld enhancement can marginally account for the AMS-02 data for the DM particle annihilating into $2\mu$ final states, while for the scalar force carrier the allowed Sommerfeld enhancement factor can be larger by a factor of 2. For the case with a pseudoscalar force carrier, the Sommerfeld enhancement factor can be very large in the resonance region, and it is possible to accommodate the AMS-02 and Fermi-LAT result for a variety of DM annihilation final states.

The Randall-Sundrum-like scenario with the small curvature $\kappa$ (RSSC model) is studied in detail in comparison with the original RS1 model. In the framework of the RSSC model, the $p_{\perp }$ distributions for dilepton production at the LHC are calculated. Both dielectron and dimuon events are taken into account. The important feature of calculations is the account of the widths of massive graviton excitations. For the summary statistics taken at 7 TeV ($L=5{\mathrm{fb}}^{-1}$) and 8 TeV ($L=20{\mathrm{fb}}^{-1}$), the exclusion limit on the five-dimensional gravity scale $M_5$ is set to be 6.84 TeV at 95% C.L. For $\sqrt{s}=13\mathrm{TeV}$ and integrated luminosity $30{\mathrm{fb}}^{-1}$, the LHC search limit is found to be 10.16 TeV. These bounds on $M_5$ are independent of $\kappa$ (up to powerlike corrections), provided $\kappa \ll M_5$.

We study potential new physics effects in the $\overline{B}\to D^{(*)}\tau \overline{\nu }$ decays. As a particular example of new physics models, we consider the class of leptoquark models and put the constraints on the leptoquark couplings using the recently measured ratios $R(D^{(*)})=\mathcal{B}(\overline{B}\to D^{(*)}\tau \overline{\nu })/\mathcal{B}(\overline{B}\to D^{(*)}\mu \overline{\nu })$. For consistency, some of the constraints are compared with the ones coming from the current experimental bound on $\mathcal{B}(B\to X_s\nu \overline{\nu })$. In order to discriminate various new physics scenarios, we examine the correlations between different observables that can be measured in the future.

We consider the decay of a polarized top quark into a stable $W^{+}$ boson and charmed-flavored (D) or bottom-flavored (B) hadrons via $t(\uparrow )\to W^{+}+D/B+X$. We study the angular distribution of the scaled energy of B/D hadrons at next-to-leading order, considering the contribution of bottom and gluon fragmentations into the heavy mesons B and D. To obtain the energy spectrum of B/D hadrons, we present our analytical expressions for the parton-level differential decay widths of $t(\uparrow )\to b+W^{+}(+g)$ at next-to-leading order. A comparison of our predictions with data at the LHC enables us to test the universality and scaling violations of the B- and D-hadron fragmentation functions. These can also be used to determine the polarization states of top quarks, and since the energy distributions depend on the ratio $m_W/m_t$, we advocate the use of such angular decay measurements for the determination of the top quark’s mass.

We obtain constraints on the mixing of vectorlike quarks coupling predominantly to the third generation. We consider all (seven) relevant types of vectorlike quarks, individually. The constraints are derived from oblique corrections and $Z\to b\overline{b}$ measurements at the Large Electron-Positron (LEP) Collider and the Stanford Linear Collider. We investigate the implications of these constraints on LHC phenomenology, concerning the decays of the heavy quarks and their single production. We also explore indirect effects of heavy quark mixing in top and bottom couplings. A remarkable effect is the possibility of explaining the anomalous forward-backward asymmetry in $Z\to b\overline{b}$ at the LEP with a hypercharge $-5/6$ doublet. We also study the impact of the new quarks on single Higgs production at the LHC and Higgs decay.

We adopt a nonperturbative relativistic constituent-quark model for the $\pi$-meson electromagnetic form factor, which has successfully predicted experimental results, and supplement it with the effective momentum-dependent quark mass to study quantitatively the transition to the perturbative QCD asymptotics. The required asymptotical behavior (including both the $Q^{-2}$ falloff and the correct coefficient) settles down automatically when the quark mass is switched off; however, the present experimental data on the form factor suggest that this cannot happen at the values of the momentum transfer below $\sim 10{\mathrm{GeV}}^2$. The effective constituent-quark mass below this scale acquires substantial nonperturbative contributions.