Modern Physics Letters A

The aim of this brief review is twofold. First, we give an overview of the unprecedented experimental efforts to measure the gravitational acceleration of antimatter; with antihydrogen, in three competing experiments at CERN (AEGIS, ALPHA and GBAR), and with muonium and positronium in other laboratories in the world. Second, we present the 21st Century’s attempts to develop a new model of the Universe with the assumed gravitational repulsion between matter and antimatter; so far, three radically different and incompatible theoretical paradigms have been proposed. Two of these three models, Dirac–Milne Cosmology (that incorporates CPT violation) and the Lattice Universe (based on CPT symmetry), assume a symmetric Universe composed of equal amounts of matter and antimatter, with antimatter somehow “hidden” in cosmic voids; this hypothesis produced encouraging preliminary results. The heart of the third model is the hypothesis that quantum vacuum fluctuations are virtual gravitational dipoles; for the first time, this hypothesis makes possible and inevitable to include the quantum vacuum as a source of gravity. Standard Model matter is considered as the only content of the Universe, while phenomena usually attributed to dark matter and dark energy are explained as the local and global effects of the gravitational polarization of the quantum vacuum by the immersed baryonic matter. An additional feature is that we might live in a cyclic Universe alternatively dominated by matter and antimatter. In about three years, we will know if there is gravitational repulsion between matter and antimatter; a discovery that can forever change our understanding of the Universe.

The nucleon is naturally viewed as a bipartite system of valence spin — defined by its non-vanishing chiral charge — and non-valence or sea spin. The sea spin can be traced over to give a reduced density matrix, and it is shown that the resulting entanglement entropy acts as an order parameter of chiral symmetry breaking in the nucleon. In the large-$N_c$ limit, the entanglement entropy vanishes and the valence spin accounts for all of the nucleon spin, while in the limit of maximal entanglement entropy, the nucleon loses memory of the valence spin and consequently has spin dominated by the sea. The nucleon state vector in the chiral basis, fit to low-energy data, gives a valence spin content consistent with experiment and lattice QCD determinations, and has large entanglement entropy.

In this paper, we have studied particle collision around a rotating acoustic black hole in 2 + 1 dimensions. This black hole is analog to a fluid flow in a draining bath tub with a sink. Center of mass energy for two-particle collision at the horizon of the rotating acoustic black hole is considered. There is a possibility of the two-mass collision to create infinite center of mass energy for certain fine tuning of the parameters of the theory.

We provide a time-dependent Dyson map and metric for the two-dimensional harmonic oscillator with a non-Hermitian ixy coupling term. This particular time-independent model exhibits spontaneously broken ${𝒫}{𝒯}$-symmetry and becomes unphysical in the broken regime, with the spectrum becoming partially complex. By introducing an explicit time dependence into the Dyson map, we provide a time-dependent metric that renders the model consistent across the unbroken and broken regimes.

It has been found that the geometrical diagnostic methods can break the degeneracy for dark energy models. In this paper, we investigate the Om diagnostic, the statefinder hierarchy $S_n$ and the composite null diagnostic $\{S_n,𝜖\}$ for the Tsallis holographic dark energy models with interactions. We find that model parameters and the forms of interaction will influence the values of diagnostic parameters or the trends of the evolutionary trajectories for each model. Moreover, the statefinder hierarchy $S_3^{(1)}$ together with $\{S_3^{(1)},𝜖\}$ could give good diagnostic results. Furthermore, we also obtain some issues of cosmological structure by means of the composite null diagnostic.

In this paper, we study how geometrical coupling can be adapted to localize a model with kinetic gauge mixing on a thin membrane. The model discussed is a theory for millicharged particles, proposed by Holdom in 1985, and that now is object of study in the LHC. We propose a geometrical coupling between the gauge fields, the Ricci scalar and the Ricci tensor. We show that it is possible to localize such a model by regarding specific values for the coupling constants. We find the solutions for the two gauge fields and discuss the localization for scalar fields that appears naturally in the process. We show that not necessarily the gauge and scalar fields are localized at the same time.

In this paper, we generalize our previous model (arXiv:1705.09331), on a hidden conformal symmetry of smooth braneworld scenarios, to the case with two real scalar fields non-minimally coupled to gravity. The gauge condition reduces the action of the system to the action where gravity minimally couples to one of the scalar fields, plus a cosmological constant. We show that, depending on the internal symmetry of the scalar fields, the two possibilities, SO(2) or SO(1, 1), emerge. In the SO(2) case, we get a ghost-like scalar field action, which can describe two models — Standing Wave and Sine-Gordon smooth braneworlds. For the SO(1, 1) case we get the standard sign for the kinetic part of the scalar field. By breaking the SO(1, 1) symmetry (but keeping the conformal one) we are able to get two Randall–Sundrum models, with a non-minimal coupling and with a scalar field having hyperbolic potential. We conclude that this method can be seen as a solution-generating technique and a natural way to introduce nontrivial scalar fields that can provide smooth braneworld models.

Recently, a one-parameter extension of the covariant Heisenberg algebra with the extension parameter $l$ $(l$ is a non-negative constant parameter which has a dimension of ${[momentum]}^{-1})$ in a $(D+1)$-dimensional globally flat spacetime has been presented which is a covariant generalization of the Kempf–Mangano algebra [see G. P. de Brito, P. I. C. Caneda, Y. M. P. Gomes, J. T. Guaitolini Junior and V. Nikoofard, Adv. High Energy Phys. 2017, 4768341 (2017) and A. Kempf and G. Mangano, Phys. Rev. D 55, 7909 (1997)]. The Abelian Proca model is reformulated from the viewpoint of the above one-parameter extension of the covariant Heisenberg algebra. It is shown that the free space solutions of the above modified Proca model describe two massive vector particles with different effective masses ${{ℳ}}_{\pm }(\mathrm{\Lambda })$ where $\mathrm{\Lambda }=\hslash l$ is the characteristic length scale in our model. In addition, the Feynman propagator in momentum space for the modified Abelian Proca model is calculated analytically. Our numerical estimations show that the maximum value of $\mathrm{\Lambda }$ in a four-dimensional spacetime is near the electroweak length scale, i.e. ${\mathrm{\Lambda }}_{max}\sim l_{\mathrm{\text{electroweak}}}\sim 10^{-18}\mathrm{\text{m}}$. We show that in the infrared/large-distance domain, the modified Proca model behaves like an Abelian massive Lee–Wick model which has been presented by Accioly and his co-workers in A. Accioly, J. Helayel-Neto, G. Correia, G. Brito, J. de Almeida and W. Herdy, Phys. Rev. D 93, 105042 (2016). The short-distance behavior of the modified Proca model is studied in the massless limit and the explicit forms of the inhomogeneous infinite derivative Maxwell equation and the infinite derivative Poisson equation are obtained. Finally, note that in the low-energy limit $(\mathrm{\Lambda }\to 0)$, the results of this paper are compatible with the results of the usual Proca model.

The nuclear isotopic structure can be understood easily via the intermediate-energy charge exchange reactions of (p, n) and ${(}^3$He, $t)$ type. In the current contribution, we present some results for charge exchange reactions induced by ³He on targets lying in mass region $18\le A\le 208$ within the theoretical framework of plane wave impulse approximation (PWIA) and distorted wave impulse approximation (DWIA). Here, the recoil effects in PWIA have also been considered. Particularly, the angular distributions and the unit cross-sections have been calculated and compared with the available data. Further, the importance of inclusion of the exchange contribution in these reactions is also considered, which eventually enhance the matching with data.

We examine the impact of the non-Markovian environment on the dynamical behavior of the quantum coherence and entropy squeezing considering a two-level atomic system (qubit) immersed in a reservoir with zero-temperature for two types of non-Markovian environments. We consider a cavity little off-resonance with the transition frequency of the qubit and the case of a non-perfect photonic band gap (PBG). We show that the amount of coherence is dependent on the structure of the environment and influenced through the memory effects. We obtain that the delay and revival of the coherence loss might take place by controlling the detuning of the cavity-qubit system. Whereas, a partial coherence trapping occurs in non-ideal PBG and the decrease of the gap width will destroy the coherence. On the other hand, we show the situation for which the squeezing is occurring and enhanced with respect to the main parameters for the system. Finally, we display the monotonic dependence of the quantum coherence and squeezing on the main model parameters.

Lackadaisical quantum walk (LQW) has been an efficient technique in searching for a target state in a database which is distributed in a two-dimensional lattice. We numerically study the quantum search algorithm based on the lackadaisical quantum walk in one and two dimensions. It is observed that specific values of the self-loop weight at each vertex of the graph is responsible for such a speedup of the algorithm. Searching for a target state in one-dimensional lattice with periodic boundary conditions is possible using lackadaisical quantum walk, which can find a target state with ${𝒪}(1)$ success probability after ${𝒪}(N)$ time steps. In two dimensions, our numerical simulation up to $M=6$ for specific sets of target states suggests that the lackadaisical quantum walk can search one of the $M$ target states in ${𝒪}\left(\sqrt{\frac{N}{M}log\frac{N}{M}}\right)$ time steps.

In 2018, Song et al. [Quantum Inf. Process 17, 244 (2018)] proposed a dynamic quantum direct secret sharing (DQDSS) protocol based on generalized GHZ states. However, this protocol is vulnerable to a security problem, known as the collusion attack, using which the dishonest agents can collude to reveal the master key without collaborating with other agents. This security problem, if unaddressed, can prevent the protocol from providing the secret sharing function. Therefore, this study proposes an improved DQDSS protocol to address the security problem in Song et al.’s DQDSS protocol. The proposed DQDSS protocol is resistant to the collusion attack and various other common attacks. Furthermore, the advantages of Song et al.’s DQDSS protocol are retained in the proposed scheme.