International Journal of Modern Physics A

Controlling longitudinal beam loss is crucial for ensuring the stable operation of superconducting linacs. Measuring and optimizing longitudinal acceptance are effective methods to reduce longitudinal beam loss. The SNS has reported research results on measuring longitudinal acceptance in a high-energy accelerator. Compared to high-energy accelerators, low-energy accelerators exhibit stronger space charge effects and nonlinearities, larger beam sizes, and more significant impacts from errors. Therefore, the measurement and optimization of longitudinal acceptance are more essential for beam loss control in low-energy superconducting linacs. This paper systematically investigates the measurement of longitudinal acceptance in low-energy superconducting linacs and validates the longitudinal acceptance measurement based on phase and energy acceptance scans through numerical simulation on the CAFe superconducting linac. Additionally, the impact of errors under actual operating conditions on the longitudinal acceptance is comprehensively analyzed. The research results indicate that conducting experiments to measure the longitudinal acceptance of a low-energy superconducting linac is highly feasible.

Motivated by recent discussions of entanglement in the context of high energy scattering, we consider the relation between the entanglement entropy of a highly excited state of a quantum system and the classical entanglement entropy of the corresponding classical system. We show on the example of two weakly coupled harmonic oscillators that the two entropies are equal. Quantum mechanically, the reduced density matrix which yields this entropy is close to the maximally entangled state. We thus observe that the nature of entanglement in this type of state is purely classical.

In this paper, we have explored a transitioning cosmic model, depicting late-time accelerated expansion in the $f(R,T^{\varphi })$ theory of gravity for an isotropic and homogeneous universe, where the trace of the energy–momentum tensor $T^{\varphi }$ is the function of the self-interacting scalar field $\varphi$. We have proposed an explicit solution to the derived model by utilizing a scale factor of the hybrid form $a(t)=t^{\alpha }{e}^{\beta t}$, where $\alpha$ and $\beta$ are constants. To estimate the best-fit values of model parameters, statistical analysis based on the Markov Chain Monte Carlo (MCMC) method has been employed on 57 $H(z)$ points in the range $0.07\le z\le 2.36$ and Pantheon Sample consisting of a total of 1048 SNe Ia in the range of $0.01<z<2.3$. We have described the dynamical features of the model, like energy density, cosmic pressure, and the equation of state parameter, in the context of the scalar field $\varphi$. We have also described the potential and behavior of the scalar field for quintessence and phantom scenarios. For the joint dataset of OHD and Pantheon, the deceleration parameter depicts a transitioning universe with signature flipping at $z_t=0.78$ with the present value of the deceleration parameter $q_0=-0.565$. The violation of SEC for the derived model indicates cosmic expansion at a faster rate. We have used state-finders to diagnose the model. The findings for our theoretical model indicate that the derived model agrees with observed findings within a particular range of limitations.

In this paper, we study the contribution of color correlations to Double Parton Scattering (DPS). We show that there is a specific class of Feynman diagrams related to so-called $1\to 2$ processes when the contribution of these color correlations is not Sudakov suppressed with the transverse scales. The effective absence of Sudakov suppression gives hope that although they are small relative to color singlet correlations, they eventually can be observed.

Rare and exotic decay modes of the Higgs boson are one kind of interesting decay processes, which can be used as a tool to further test the SM and search for new physics phenomena. In this paper, considering the constraints on the $HZa$ coupling from the relevant LHC data, we calculate the contributions of the light axion-like particle (ALP) with mass less than 200MeV to the rare Higgs decays $H\to \nu \overline{\nu }\gamma$, $H\to {\ell }^{+}{\ell }^{-}\gamma$ and $H\to Z\nu \overline{\nu }$. Our numerical results show that the light ALP can indeed generate significantly contributions to these decay processes. The value of the branching ratio $\mathrm{\text{Br}}(H\to \nu \nu \gamma )$ induced only by ALP is larger than the SM prediction at least one order of magnitude. We expect that our results might be helpful to test the indirect signals of light ALP in near future collider experiments, particularly in future lepton collider experiments.

A randomly generated complex symmetric matrix using the adaptive Monte Carlo method is taken as a general form of Majorana neutrino mass matrix, which is diagonalized by the use of eigenvectors. We extract all the neutrino oscillation parameters, i.e. two mass-squared differences ($\mathrm{\Delta }{m}_{21}^2$ and $\mathrm{\Delta }{m}_{32}^2$), three mixing angles (${\theta }_{12}$, ${\theta }_{13}$, ${\theta }_{23}$) and three phases, i.e. one Dirac CP violating phase (${\delta }_{\mathrm{\text{CP}}}$) and two Majorana phases (${\alpha }_1$ and ${\alpha }_2$). The Charge-Parity (CP) violating phases are extracted from the mixing matrix constructed with the eigenvectors of the Hermitian matrix formed by the complex symmetric mass matrix. All the latest neutrino oscillation parameters within 3$\sigma$ bound are only allowed in Normal Hierarchy (NH) consistent with the latest Planck cosmological upper bound, $\sum |m_i|<0.12$eV. Three cases of one-zero texture i.e. $m_{11}=0$, $m_{12}=0$, $m_{13}=0$ and two cases of two-zero texture, i.e. $m_{11},m_{12}=0$ and $m_{11},m_{13}=0$ are allowed in normal hierarchy whereas none of zero texture is allowed in inverted hierarchy. We also study effective neutrino masses $m_{\beta }$ in tritium beta decay and $m_{\beta \beta }$ in neutrinoless double beta decay and calculate numerically the allowed range of mass elements of Majorana mass matrix.

An attempt to directly use the synchronous gauge ($g_{0\lambda }=-{\delta }_{0\lambda }$) in perturbative gravity leads to a singularity at $p_0=0$ in the graviton propagator. This is similar to the singularity in the propagator for Yang–Mills fields $A_{\lambda }^a$ in the temporal gauge ($A_0^a=0$). There the singularity was softened, obtaining this gauge as the limit at $\epsilon \to 0$ of the gauge $n^{\lambda }{A}_{\lambda }^a=0$, $n^{\lambda }=(1,-\epsilon {({\partial }^j{\partial }_j)}^{-1}{\partial }^k)$. Then the singularities at $p_0=0$ are replaced by negative powers of $p_0\pm i\epsilon$, and thus we bypass these poles in a certain way. Now consider a similar condition on $n^{\lambda }{g}_{\lambda \mu }$ in perturbative gravity, which becomes the synchronous gauge at $\epsilon \to 0$. Unlike the Yang–Mills case, the contribution of the Faddeev–Popov ghosts to the effective action is nonzero, and we calculate it. In this calculation, an intermediate regularization is needed, and we assume the discrete structure of the theory at short distances for that. The effect of this contribution is to change the functional integral measure or, for example, to add nonpole terms to the propagator. This contribution vanishes at $\epsilon \to 0$. Thus, we effectively have the synchronous gauge with the resolved singularities at $p_0=0$, where only the physical components $g_{jk}$ are active and there is no need to calculate the ghost contribution.

In this paper, we calculate exactly the solution of Klein–Gordon equation in anti-de Sitter space–time. Due to spherical symmetry, the angular wave functions are given by spherical harmonics. The radial wave functions are given by local Heun functions. We analyze the behavior of the radial wave function in regions near three possible event horizon positions $(r_0,r_1,r_2)$ and investigate the decay rate, Hawking radiation and Hawking temperature for these three cases. Comparing the results, we verify that if the decay rate and Hawking radiation are greater, then the closer the event horizon is to the singularity of the black hole. Finally, we analyze the special case of a small black hole limit.

Within the scope of a Bianchi type-I (BI) cosmological model, we study the interacting system of spinor and electromagnetic fields and its role in the evolution of the Universe. In some earlier studies, it was found that in the case of a pure spinor field, the presence of nontrivial nondiagonal components of energy–momentum tensor (EMT) leads to some severe restrictions both on the space–time geometry and/or spinor field itself, whereas in the case of electromagnetic field with induced nonlinearity, such components impose severe restrictions on metric functions and the components of the vector potential. It is shown that in the case of interacting spinor and electromagnetic fields, the restrictions are not as severe as in the other cases and in this case, a nonlinear and massive spinor field with different components of vector potential can survive in a general Bianchi type-I space–time.