Modern Physics Letters A

In 2008, Michigan State University was selected to establish the Facility for Rare Isotope Beams (FRIB). Construction of the FRIB accelerator was completed in January 2022. Phased accelerator commissioning with heavy ion beams started in 2017 with the normal-conducting ion source and radio-frequency quadrupole. In April 2021, the full FRIB driver linear accelerator (linac) was commissioned, with heavy ion beams accelerated to energies above 200 MeV/nucleon by 324 superconducting radiofrequency (SRF) resonators operating at 2 K and 4 K with liquid-helium cooling. In preparation for high-power operation, a liquid lithium charge stripper was commissioned with heavy ion beams up to uranium-238, followed by the simultaneous acceleration of multiple-charge-state heavy ion beams to energies above 200 MeV/nucleon. In December 2021, selenium-84 was produced with the FRIB target using a krypton-86 primary beam, demonstrating FRIB’s capability for scientific discovery.

The characteristic axion couplings could be generated via effective couplings between the Standard Model (SM) fermions to a pseudo-Goldstone from a high-scale U(1) Peccei–Quinn (PQ) symmetry breaking. Assuming that the UV-induced effective operators generate necessary couplings before the PQ symmetry breaking, and any low-scale couplings to the SM are restricted to the Yukawa sector, three minimal natural scenarios can be formulated, which provide a connection between the QCD axions and mediators at the GUT/string scales. We find that the PQ symmetry breaking scale could be about $10^{15}$ GeV, higher than the classical QCD dark matter axion window but possible if the anthropic window is considered. We also propose an experiment to probe such scenarios. If the dark matter axion is discovered, they might suggest that we live in an atypical Hubble volume.

We point out that the bootstrap program in quantum mechanics proposed by Han et al. reduces to a bootstrap study of a microcanonical ensemble of the same Hamiltonian in the $\hslash \to 0$ limit. In the limit, the quantum mechanical archipelago becomes an extremely thin line for an anharmonic oscillator. For a double-well potential, a peninsula in $E\le 0$ appears.

Where is the anti-matter in our universe? This is the most significant open problem of the modern era. This paper is devoted to the study of cosmological impact of gravitational baryogenesis and its generalized case driven by [Davoudiasl et al., Phys. Rev. Lett. 93, 201301 (2004)]. In this class of baryogenesis, the Ricci scalar $R$ is derivatively coupled to the baryon current $J_B$ as $({\partial }_{i}R)J_B^i$. We examine the imbalance of baryon and anti-baryon of the universe in the context of $f(T,\mathrm{\Theta })$ gravity, where $T$ and $\mathrm{\Theta }$ are the torsion scalar and the trace of the energy–momentum tensor, respectively. We assume two $f(T,\mathrm{\Theta })$ models in which the first one contains the sum of second-order torsion tensors and the trace of energy–momentum tensor while the second one is the product of these terms. For all cases, we find the ratio of baryon number to entropy by considering the power-law scale factor. Finally, we compare our results with the observational value of baryon-number-density-to-entropy ratio. The baryon-to-entropy ratio against the first model lies in the range $7.5_{-3.5}^{+3.5}\times 10^{-11}$ while for the second model it contains $1.5_{-1.45}^{+1.5}\times 10^{-10}$. For generalized case of gravitational baryogenesis, we also obtain results that are compatible with the observation limit.

In this paper, we investigate the generalized symmetric, static compact objects under anisotropic fluid in the background of Karmarkar embedding class-1 condition. To find the exact solutions of the modified field equations, we consider the gravitational Lagrangian as a linear function of the Ricci scalar and the trace of the stress–energy tensor, i.e. $f({ℛ},{𝒯})={ℛ}+\lambda {𝒯}$, where $\lambda$ is a constant. By employing the concept of Karmarkar condition, we calculate a $g_{tt}$ metric component, while for a specific form of $g_{rr}$, the gravitational potential is chosen. To attain the closed-form solutions of the modified field equations, we match the interior spacetime metric with the exterior Schwarzschild metric at the boundary and using the numerical values of mass and radius of the compact stars like PSR J1903+327, 4U 1820-30, LMC X-4, and EXO 1785-248, we constraint some unknown parameters. We have discussed physical stability of the stellar configuration by adopting the energy bounds, Tolman–Oppenheimer–Volkov (TOV) equation, adiabatic index, central density and pressure as well. It is concluded that our resulting anisotropic solutions did well behave and a reasonable degree of precision with recent observations.

In this work, we investigate the Rastall–Maxwell theory around the strange quark matter (SQM) in the presence of a quintessence field and a quintessence dark energy having a characteristic parameter $w_q$ such that $-1<w_q<-1/3$. The SQM is governed by the simplified MIT bag model equation of state: $p_r=\frac{1}{3}(\rho -4B)$, with $B$ the bag constant, in the presence of a load distribution given by $q(r)=Q{(r/R)}^3=\alpha r^3$. We find some solutions by using the modified Tolman–Oppenheimer–Volkoff (TOV) equation in the framework of Rastall gravity. We investigate the energy condition, the mass–radius relation, modified TOV equation, redshift and the stability of the system is checked by exploring the adiabatic index, the compactification factor and the causality condition for verifying the physical consistency of our model. We notify that for physical values of Rastall parameter, the stellar system is more massive compared to its size. Hence, it is revealed that the alternative Rastall theory is appropriate to explain the behavior of massive stellar objects. The presence of dark energy motivates us to consider that the existing strange stars are a mixture of both ordinary matter and quintessence matter in different proportions. The incorporation of quintessence matter with the real one describes the well-known SQM.

In this paper, we study the quasinormal modes for scalar, electromagnetic, and gravitational axial perturbations in the Hayward regular black hole surrounded by quintessence (HBH-${\omega }_q$). Using the third-order WKB approximation, we can determine the dependence of the quasinormal modes on the parameters of the regular black hole and the parameters on the test fields. We also determine the greybody factor, giving transmission and reflection coefficients of the scattered wave through the effective potentials in the WKB approximation using numerical analysis.