International Journal of Modern Physics A

In this work, we study meson systems consisting of quark–antiquark. We solve Lippman–Schwinger equation numerically for heavy meson systems. We attempt to find a nonrelativistic potential model through which we can solve the quark–antiquark bound state problem. The coefficients obtained are in agreement with Martin potential coefficients. Via this method we also determine the strong coupling constant of Cornell and Yukawa potentials for the heavy meson.

We perform a comprehensive study of the Higgs potential of the two Higgs doublet model extended by a real triplet scalar field $\mathrm{\Delta }$. This model, dubbed $2\mathrm{\text{HDM}}+\mathrm{\text{T}}$, has a rich Higgs spectrum consisting of three CP-even Higgs $h_{1,2,3}$, one CP-odd $A_0$ and two pairs of charged Higgs $H_{1,2}^{\pm }$. First, we determine the perturbative unitarity constraints and a set of nontrivial conditions for the boundedness from below (BFB). Then we derive the Veltman conditions by considering the quadratic divergencies of Higgs boson self-energies in $2\mathrm{\text{HDM}}+\mathrm{\text{T}}$. We find that the parameter space is severely delimited by these theoretical constraints, as well as experimental exclusion limits and Higgs signal rate measurements at LEP and LHC. Using HiggsBounds-5.3.2beta and HiggSignals-2.2.3beta public codes, an exclusion test at $2\sigma$ is then performed on the physical scalars of $2\mathrm{\text{HDM}}+\mathrm{\text{T}}$. Our analysis provides a clear insight on the nonstandard scalar masses, showing that the allowed ranges are strongly sensitive to the sign of mixing angle ${\alpha }_1$, essentially when naturalness is involved. For ${\alpha }_1<0$ scenario, our results place higher limits on the bounds of all scalar masses, and show that the pairs $(h_2,H_1^{\pm })$ and $(h_3,H_2^{\pm })$ are nearly mass degenerate varying within the intervals $[130,246]$ GeV and $[160,335]$ GeV, respectively. When ${\alpha }_1$ turns positive, we show that consistency with theoretical constraints and current LHC data, essentially on the diphoton decay channel, favors Higgs masses varying within wide allowed ranges: $[153,973]$ GeV for $m_{A_0}$; $[151,928]$ GeV for ($m_{h_2}$, $m_{H_1^{\pm }}$) and $[186,979]$ GeV for ($m_{h_3}$, $m_{H_2^{\pm }}$). Finally, we find that the $\gamma \gamma$ and $Z\gamma$ Higgs decay modes are generally correlated if $tan\beta$ lies within the reduced intervals $17\le tan\beta \le 25$ and ${\lambda }_b$ parameter is frozen around $1.3$ ($1.1$) for $sin{\alpha }_1>0$ ($sin{\alpha }_1<0$).

In this paper, we calculate tree-level currents of created particles in strong background electric fields in 4D QED for various initial states. Namely, we do that in pulse background for initial vacuum and thermal states at past infinity. In both cases, we find that the current grows linearly with the length of the pulse with coefficients of proportionality containing the characteristic Schwinger’s factor. For the constant electric field background, we calculate the current for several different initial states. We observe that in such a case the current is either zero or linearly divergent. We explain the reason for such a behavior and compare the situation in ordinary and scalar QED. Finally, we calculate the current in two-dimensional situation in the presence of such settings when the so-called Klein paradox can be observed.

We present a next-to-leading order (NLO) relativistic correction to $B_c\to J/\psi$ tensor form factors within nonrelativistic QCD (NRQCD). We also consider complete Dirac bilinears $\bar{c}\mathrm{\Gamma }b$ with $4\times 4$ matrices $\mathrm{\Gamma }=1,{\gamma }^5,{\gamma }^{\mu },{\gamma }^{\mu }{\gamma }^5,{\sigma }^{\mu \nu }$ in the $b\to c$ transition. The relation among different current form factors is given and it shows that symmetries emerge in the heavy bottom quark limit. For a phenomenological extension, we propose to extract the long-distance matrix elements (LDMEs) for $B_c$ meson from the recent HPQCD lattice data and the NLO form factors at large momentum recoil.

We analyze the influence of a cutoff point on a Coulomb-type potential that stems from the interaction of an electron with electric fields. This cutoff point establishes a forbidden region for the electron. Then, we search for bound state solutions to the Schrödinger equation. In addition, we consider a rotating reference frame. We show that the effects of rotation break the degeneracy of the energy levels. Further, we discuss the Aharonov–Bohm effect for bound states.

We investigate Rindler’s frame measurements. From its perspective, we found a geometric/gravitational interpretation of speed of light, mass and uncertainty principle. This can be interpreted as measurements of a black hole universal clock. This led to an emergence of a timeless state of gravity in a mathematically consistent way. In other words, space may be a frozen time.

In this paper, we consider a clockwise rotating magnetic field around the $z$-axis and charge carriers which impinge normally to the $x-y$ plane. We obtained analytically the spectrum of the momentum operator $p_z$ and found the existence of a band structure from which the movement of these charge carries is filtered according to the spatial period of the magnetic field or its intensity. Also we exhibit the existence of three band gaps (one total or primary and two partials) whose width depends on the system parameters.

We examine the generalized quantum electrodynamics as a natural extension of the Maxwell electrodynamics to cure the one-loop divergence. We establish a precise scenario to discuss the underlying features between photon and fermion where the perturbative Maxwell electrodynamics fails. Our quantum model combines stability, unitarity, and gauge invariance as the central properties. To interpret the quantum fluctuations without suffering from the physical conflicts proved by Haag’s theorem, we construct the covariant quantization in the Heisenberg picture instead of the Interaction one. Furthermore, we discuss the absence of anomalous magnetic moment and mass-shell singularity.

In this paper, the null geodesic equations are computed in $d=4$ space–time dimensions [Y. Younesizadeh, A. A. Ahmad, A. H. Ahmed, F. Younesizadeh, Ann. Phys. 420, 168246 (2020)] by using the concept of symmetries and Hamilton–Jacobi equation and Carter separable method. With these null geodesics in hand, we evaluate the celestial coordinates (x, y) and the radius $R_s$ of the BH shadow and represent it graphically. In addition, we have shown that the peak of this energy slowly shifts to lower frequencies and its height decreases with the increase in the YM magnetic charge ($Q$) values and decrease in the $f(R)$ parameter ($\chi$) values. In addition, we have analyzed the concept of effective potential barrier by transforming the radial equation of motion into standard Schrodinger form. The most important result derived from this study is that the height of this potential increases with increase in the YM magnetic charge ($Q$) values. Then, we study the quasinormal modes (QNMs) of these 4D black holes. For this purpose, we use the WKB approximation method upto third-order corrections. We have shown the perturbation’s decay in corresponding diagrams when the YM magnetic charge ($Q$) values and the $f(R)$ parameter ($\chi$) values change.

We investigate the dynamics of a composite system (${𝒞}{𝒮}$) consisting of an interacting fermion–antifermion pair in the three-dimensional space–time background generated by a static point source. By considering the interaction between the particles as Dirac oscillator coupling, we analyze the effects of space–time topology on the energy of such a ${𝒞}{𝒮}$. To achieve this, we solve the corresponding form of a two-body Dirac equation (fully-covariant) by assuming the center-of-mass of the particles is at rest and locates at the origin of the spatial geometry. Under this assumption, we arrive at a nonperturbative energy spectrum for the system in question. This spectrum includes spin coupling and depends on the angular deficit parameter $({𝒜}{𝒟}{𝒫})$ of the geometric background. This provides a suitable basis to determine the effects of the geometric background on the energy of the ${𝒞}{𝒮}$ under consideration. Our results show that such a ${𝒞}{𝒮}$ behaves like a single quantum oscillator. Then, we analyze the alterations in the energy levels and discuss the limits of the obtained results. We show that the effects of the geometric background on each energy level are not same and there can be degeneracy in the energy levels for small values of the ${𝒜}{𝒟}{𝒫}$.

Assuming the standard effective-field-theoretic formulation of Hawking radiation, we show explicitly how a generic effective theory predicts a firewall from an initially uneventful horizon for a spherically symmetric, uncharged black hole in $D$ dimensions for $D\ge 4$. The firewall is created via higher-derivative interactions within the scrambling time after the collapsing matter enters the trapping horizon. This result manifests the trans-Planckian problem of Hawking radiation and demonstrates the incompatibility between Hawking radiation and the uneventful horizon.

In this paper, we have proposed a model of accelerating universe with binary mixture of bulk viscous fluid and dark energy (DE) and probed the model parameters: present values of Hubble’s constant $H_0$, equation of state paper of DE ${\omega }_{\mathrm{\text{de}}}$ and density parameter of DE ${({\mathrm{\Omega }}_{\mathrm{\text{de}}})}_0$ with recent observational $H(z)$ data (OHD) as well as joint Pantheon compilation of SN Ia data and OHD. Using cosmic chronometric technique, we obtain $H_0=69.80\pm 1.64{\mathrm{\text{km s}}}^{-1}{\mathrm{\text{Mpc}}}^{-1}$ and $70.0258\pm 1.72{\mathrm{\text{km s}}}^{-1}{\mathrm{\text{Mpc}}}^{-1}$ by restricting our derived model with recent OHD and joint Pantheon compilation SN Ia data and OHD, respectively. The present age of the universe in derived model is estimated as $t_0=13.82\pm 0.33\mathrm{\text{Gyr}}$. Also, we observe that derived model represents a model of transitioning universe with transition redshift $z_t=0.7286$. We have constrained the present value of jerk parameter as $j_0=0.969\pm 0.0075$ with joint OHD and Pantheon data. From this analysis, we observed that the model of the universe, presented in this paper, shows a marginal departure from $\mathrm{\Lambda }$CDM model.

In this work, we have studied various cosmological parameters in the presence of viscous new Tsallis holographic dark energies for interacting scenarios in the framework of Chern–Simons modified gravity. The bulk viscosity has been considered with the bulk viscous pressure chosen in the form $\mathrm{\Pi }=-3H\left(\right.{\xi }_0+{\xi }_{1}H+{\xi }_2(Ḣ+H^2)\left)\right.$. Hubble parameter $H$ has been obtained from the above choice of scale factor and in this viscous scenario, the effective pressure has been obtained in Chern–Simons framework whose field equation, cosmological consequences have been investigated. It has been observed that for the interaction scenario in the presence of bulk viscosity the EoS parameter is staying above $-1$, which indicates quintessence behavior. Hence, for the universe filled with a bulk viscous fluid can have the possibility of avoidance of big-rip, although the earlier transition from quintessence to phantom is not avoidable.