Modern Physics Letters A

Fermilab carries out an extensive program of accelerator-based high energy particle physics research at the Intensity Frontier that relies on the operation of 8 GeV and 120 GeV proton beamlines for a number of fixed target experiments. Routine operation with a world-record 700 kW of average 120 GeV beam power on the neutrino target was achieved in 2017 as a result of the Proton Improvement Plan (PIP) upgrade. There are plans to further increase the power from 900–1000 kW. The next major upgrade of the FNAL accelerator complex, called PIP-II, is under development. It aims at 1.2 MW beam power on target at the start of the LBNF/DUNE experiment in the middle of the next decade and assumes replacement of the existing 40 years old 400 MeV normal-conducting Linac with a modern 800 MeV superconducting RF linear accelerator. There are several concepts to further double the beam power to $>$ 2.4 MW after replacement of the existing 8 GeV Booster synchrotron. In this review, we discuss current performance of the Fermilab proton accelerator complex, the upgrade plans for the next two decades and the accelerator R&D program to address cost and performance risks for these upgrades.

Assuming a diagonal Majorana neutrino mass matrix, we investigate the neutrino Yukawa textures which lead to a nonzero reactor mixing angle ${𝜃}_{13}$. The neutrino effective coupling matrix ${\kappa }^{\mathrm{\text{eff}}}$ is pre-diagonalized by a constant mixing pattern $V_{\nu }$ with a vanishing ${𝜃}_{13}^{\nu }$. The resulting pre-diagonal symmetrical matrix $\kappa$ is set to be four texture zeros with two types of off-diagonal elements nonzero, which are ${\kappa }_{13}$ and ${\kappa }_{23}$, respectively. With the expectation of simple textures, we thoroughly classify the linear combinations, ${\alpha }_i$, ${\beta }_i$ and ${\gamma }_i$ of Yukawa elements ${\lambda }_{ij}$ in the same row, according to the values, vanishing or not. Each set of the classifications can lead to a Yukawa texture which may have implications for the discrete flavor model buildings. We also present a model based on $A_4$ according to one set of the constraints on the three combinations with a specific choice of a coefficient in Yukawa texture.

This paper is devoted to investigate the recently proposed modified Gauss–Bonnet $f({𝒢},T)$ gravity, with ${𝒢}$, the Gauss–Bonnet term, coupled with $T$, the trace of energy–momentum tensor. We have used the Noether symmetry methodology to discuss some cosmologically important $f({𝒢},T)$ gravity models with anisotropic background. In particular, the Noether symmetry equations for modified $f({𝒢},T)$ gravity are reported for locally rotationally symmetric Bianchi type I universe. Explicitly, two models have been proposed to explore the exact solutions and the conserved quantities. It is concluded that the specific models of modified Gauss–Bonnet gravity may be used to reconstruct $\mathrm{\Lambda }$CDM cosmology without involving any cosmological constant.

In this paper, we have studied particle collisions around a charged dilaton black hole in 2 + 1 dimensions. This black hole is a solution to the low energy string action in 2 + 1 dimensions. Time-like geodesics for charged particles are studied in detail. The center-of-mass energy for two charged particles colliding closer to the horizon is calculated and shown to be infinite if one of the particles has the critical charge.

We show that in the isentropic scenario, the first-order thermodynamical particle creation model gives an emergent universe solution even when the chemical potential is nonzero. However, there exists no emergent universe scenario in the second-order non-equilibrium theory for the particle creation model. We then point out a correspondence between the particle creation model with barotropic equation of state and the equation of state giving rise to an emergent universe without particle creation in spatially flat FRW cosmology.

We consider Heisenberg–Euler-type model of nonlinear electrodynamics with two parameters. Heisenberg–Euler electrodynamics is a particular case of this model. Corrections to Coulomb’s law at $r\to \infty$ are obtained and energy conditions are studied. The total electrostatic energy of charged particles is finite. The charged black hole solution in the framework of nonlinear electrodynamics is investigated. We find the asymptotic of the metric and mass functions at $r\to \infty$. Corrections to the Reissner–Nordström solution are obtained.

The Standard Model (SM) extensions with vector-like states which have either zero hypercharge or zero weak isospin are rather poorly constrained by the electroweak precision measurements. Such new states would however modify the running of the gauge couplings at high energies. As a result, the Drell–Yan process $pp\to {\ell }^{+}{\ell }^{-}$ at the LHC places useful constraints on these models. The relevant observables include both the dilepton invariant mass distribution $M_{\ell \ell }$ and the forward–backward asymmetry $A_{\mathrm{\text{FB}}}$. We find that the LHC Run 1 data and the initial data from Run 2 surpass the sensitivity of LEP and already put meaningful constraints on the existence of such particles, which will become progressively stronger with more data.