International Journal of Modern Physics A

We present novel classes of nonstationary solutions to the five-dimensional generalized Einstein–Maxwell-dilaton theory with cosmological constant, in which the Maxwell’s field and the cosmological constant couple to the dilaton field. In the first class of solutions, the two nonzero coupling constants are different, while in the second class of solutions, the two coupling constants are equal to each other. We find consistent cosmological solutions with positive, negative or zero cosmological constant, where the cosmological constant depends on the value of one coupling constant in the theory. Moreover, we discuss the physical properties of the five-dimensional solutions and the uniqueness of the solutions in five dimensions by showing the solutions with different coupling constants cannot be uplifted to any Einstein–Maxwell theory in higher dimensions.

The electroweak unification group $G\equiv SU{(2)}_L\times U{(1)}_e\times U{(1)}_{\mu }\times U{(1)}_{\tau }$ in which each fermion multiplet has its own $U(1)$ factor was proposed in 1986 to get the neutrino mass matrix. In this paper, the gauge group $G$ is restricted to lepton section only, leaving quark multiplets as in the Standard Model. In addition to lepton multiplets $L_e$, $L_{\mu }$ and $L_{\tau }$, there are three $SU(2)$ singlet right-handed neutrinos $N_R^{(i)}$’s. With the breaking of $G$ to $SU{(2)}_L\times U(1)$, the right-handed neutrinos acquire heavy Majorana masses. Three heavy right-handed neutrinos $N_R^{(i)}$’s are available to generate a $3\times 3$ nondiagonal neutrino mass matrix in terms of three Yukawa couplings $h_1^{(2)}$, $h_2^{(3)}$, $h_3^{(1)}$ of the Higgs scalar doublet to $L_e$, $L_{\mu }$, $L_{\tau }$ with $N_R^{(1)}$, $N_R^{(2)}$ and $N_R^{(3)}$, respectively. Three Yukawa couplings can be arranged and expressed in terms of masses $m_e$, $m_{\mu }$, $m_{\tau }$ in three different ways to obtain the results of interest for Case 1: $({\nu }_e\to {\nu }_{\tau })$; Case 2: $({\nu }_e\to {\nu }_{\mu })$; Case 3: $({\nu }_{\mu }\to {\nu }_{\tau })$. The results obtained for the three cases are compared with the experimental data from neutrino oscillations. Cases 1 and 2 are relevant for solar neutrino oscillations whereas Case 3 is relevant for atmospheric neutrino oscillations.

Electron–positron annihilation into a pair of top quarks is considered at the energy of the future collider CLIC. Polarization components of the top quark are calculated with the $\gamma t\bar{t}$ and $Zt\bar{t}$ interactions which follow from the Lagrangian of the effective field theory of the Standard Model. The polarization vector as a function of the scattering angle is calculated and averaged components of polarization are analyzed as functions of anomalous coupling constants. Extrema of these observables (maxima, minima and saddle points) are studied as functions of the $e^{+}{e}^{-}$ energy.

It is advocated that geometry of the interaction region of two heavy nuclei colliding at large impact parameters is important for the relative role of light-by-light scattering and QCD-initiated processes. Exclusive production of resonances is possible by dense electromagnetic fields in the interior space between the nuclei. The cross-section of the two-photon processes is evaluated and some examples are considered. It is speculated that the exclusive production of ${\rho }^0$-mesons by “two-photon” processes forbidden by the Landau–Yang rule may be allowed within strong magnetic fields due to odd number of photons becoming involved.

Charm and bottom particles are rare in Extensive Air Showers, but their effects can be radical on the EASs development. If such particles show up with a large fraction of primary energy, they can reach large atmospheric depths, depositing energy in deeper layers of the atmosphere. That will cause changes at the EAS observables ($X_{max}$, RMS and $N_{max}$), besides a considerable change in the shape of longitudinal profile energy deposit in the atmosphere. We are using for this work a modified code of an EAS simulator, CORSIKA, with production of charm and bottom particles at the first interaction of the primary cosmic ray. We will show in this paper some results to different $x_F$ values and different production models.

We study some aspects of linearized gravity as gauge theory, with massive deformation. Recently, it has been shown that there are two distinct solutions, which represent physical massive gravity. The purpose of the present work is to show that these two seemingly discrete solutions are equivalent at the level of generating functional. The significance of this simple work lies in the fact that one solution represents physical massive gravity at Fierz–Pauli (FP) point and the other outside the FP point.

In this work, we solve the time-independent Schrödinger equation for a Landau system modulated by a non-Hermitian Hamiltonian. The system consists of a spinless particle in a uniform magnetic field submitted to action of a non-${𝒫}{𝒯}$ symmetric complex potential. Although the Hamiltonian is neither Hermitian nor ${𝒫}{𝒯}$-symmetric, we find that the Landau problem under study exhibits an entirely real energy spectrum.