International Journal of Modern Physics A

We present research on radiative decays of vector $(J^{PC}=1^{--})$ to pseudoscalar $(J^{PC}=0^{-+})$ particles ($u$, $d$, $s$, $c$, $b$, $t$ quark system) using broken symmetry techniques in the infinite-momentum frame and equal-time commutation relations and the $SU(6)$ Lie algebra, and conducted without ascribing any specific form to meson quark structure or intra-quark interactions. We utilize the physical electromagnetic current $j_{\mathrm{\text{em}}}^{\mu }(0)$ including its singlet $U(1)$ term and focus on the $SU(6)$ 35-plet. We derive new relations involving the electromagnetic current (including its singlet — proportional to the $SU(6)$ singlet). Remarkably, we find that the electromagnetic current singlet plays an intrinsic role in understanding the physics of radiative decays and that the charged and neutral $\rho$ meson radiative decays into $\pi \gamma$ are due entirely to the singlet term in $j_{\mathrm{\text{em}}}^{\mu }(0)$. Although there is insufficient radiative decay experimental data available at this time, parametrization of possible predicted values of $\mathrm{\Gamma }(D^{\ast 0}\to D^0\gamma )$ is made. For conciseness and self-containment, we compute all $SU(6)$ Lie algebra simple roots, positive roots, weights and fundamental weights which allow the construction of all $SU(6)$ representations. We also derive all nonzero $SU(6)$ generator commutators and anticommutators — useful for further research on grand unified theories.

Considering the recent experimental results on exclusive semileptonic $B$ meson decays showing sizable departure from their Standard Model prediction of lepton flavor universality and keeping ongoing and proposed nonstandard Higgs searches in mind, we explore the charged current flavor observables $\left({{ℛ}}_{D^{(\ast )}},{{ℛ}}_{J/\psi }\right)$, among other $b\to c\ell \nu$ transitions, in the presence of a relevant scalar current effective new physics operator. We use $B_c$ lifetime and predicted bounds on the branching fraction of $B_c\to \tau \nu$ decay as constraints. We show the allowed parameter space in terms of the real and imaginary parts of the corresponding Wilson coefficients for such interactions. Under the light of obtained results, we study the prospect of two benchmark models, rendering the Wilson coefficients real (Georgi–Machacek (GM)) and complex (leptoquark (LQ)), respectively. We show that constraints from $b\to c\ell \nu$ on GM parameters are consistent with other flavor constraints on the model, if we drop the Babar results. Including those that disfavors the model by more than $3\sigma$. On the other hand, one benchmark LQ scenario, which gives rise to a single scalar current effective interaction, is still allowed within $68\%$ confidence level, albeit with a shrunk parameter space.

Light front (LF) Hamiltonian for QED in $(1+1)$ dimensions is constructed using the boson form of this model with additional Pauli–Villars-type ultraviolet regularization. Perturbation theory, generated by this LF Hamiltonian, is proved to be equivalent to usual covariant chiral perturbation theory. The obtained LF Hamiltonian depends explicitly on chiral condensate parameters which enter in a form of some renormalization of coupling constants. The obtained results can be useful when one attempts to apply LF Hamiltonian approach for $(3+1)$-dimensional models like QCD.

In this contribution, we study the effects of space noncommutativity on the Landau system for a neutral particle with induced electric dipole moment subject to a linear confining potential. We analytically solve the Schrödinger equation and obtain the complete set of energy levels and the corresponding radial wave functions for the system in terms of the noncommutativity parameter $𝜃$.

We search for relativistic quantum phases for a Dirac neutral particle with a permanent magnetic dipole moment in the cosmic string space–time under the effects of the violation of the Lorentz symmetry. This general relativity background is built based on the modified Maxwell theory coupled to gravity. Hence, we analyze analogues of the scalar Aharonov–Bohm effect for neutral particles in two different scenarios of the Lorentz symmetry violation in the cosmic string space–time.

The functional renormalization group treatment is presented for the two-dimensional sine-Gordon model including a bilocal term in the potential, which contributes to the flow at the tree level. It is shown that the flow of the bilocal term can substitute the evolution of the wave function renormalization constant, since it can recover the Kosterlitz–Thouless type phase transition. The flows can also reveal the connection between the sine-Gordon and the noninteracting Thirring models at a special value of the wave number parameter.

The measurement of Born cross-section of $e^{+}{e}^{-}\to ZH$ process is one of the major goals of the future Circular Electron Positron Collider, which may reach a precision of 0.5% at 240 GeV. Such unprecedented precision must be guaranteed by both theoretical and experimental sides, such as the calculations of high order corrections, the knowledge of the ${\sigma }^{\mathrm{\text{B}}}(e^{+}{e}^{-}\to ZH)$ line shape. Uncertainty of the radiative correction factor at 240 GeV caused by the ${\sigma }^{\mathrm{\text{B}}}(e^{+}{e}^{-}\to ZH)$ line shape is evaluated in this work. Therefore, dedicated data-taking schemes are proposed in order to precisely calculate the ISR correction factor.