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In the present work, one analyzes two systems trying to obtain physical conditions where some properties attributed to negative mass can be mimicked by positive mass particles. The first one is the well-known 1/2-spin system described by the Dirac equation in the presence of an external electromagnetic field. Assuming some physical restrictions, one obtains that the use of $e\rightarrow-e$ can lead to the same results as using $m\rightarrow-m$. In particular, for a null dielectric function, it is possible to obtain a negative mass behavior from a positive mass system composed of negatively charged particles. The second system is based on the de Broglie matter wave. The dispersion relation of such a wave can be negative (real or imaginary valued) if one assumes an imaginary wavenumber. The consequence is the emergence of a negative refractive index for positive mass particles. However, this behavior is generally attributed to a negative mass system., Comment: 12 pages, no figures

This work examines some aspects related to the existence of negative mass. The requirement for the partition function to converge leads to two distinct approaches. Initially, convergence is achieved by assuming a negative absolute temperature, which results in an imaginary partition function and complex entropy. Subsequently, convergence is maintained by keeping the absolute temperature positive while introducing an imaginary velocity. This modification leads to a positive partition function and real entropy. It seems the utilization of imaginary velocity may yield more plausible physical results compared to the use of negative temperature, at least for the partition function and entropy., Comment: A version of this manuscript was accepted for publication in Mod. Phys. Lett. A

We propose to apply the entropy generation $(\dot S_{gen}$) concept to a mechanical system: the well-known simple pendulum. When considering the ideal case, where only conservative forces act on the system, one has $\dot S_{gen}=0$, and the entropy variation is null. However, as shall be seen, the time entropy variation is not null all the time. Considering a non-conservative force proportional to the pendulum velocity, the amplitude of oscillations decreases to zero as $t$ grows. In this case, $\dot S_{gen}>0$ indicates that it is related to energy dissipation, as stated by the Gouy-Stodola theorem. Hence, as shall be seen, the greater the strength of the non-conservative force, the greater are both the energy dissipation and the time rate of entropy variation.

In this work, we use the Gouy-Stodola theorem to calculate the entropy production rate in the inflationary epoch of the universe. This theorem allows us the simple calculation of entropy and entropy production rate occasioned by the decaying of the inflaton scalar field. Both the entropy and entropy production rate achieve large values, agreeing with the expected values present in the literature.

In this paper, one presents some results concerning the behavior of the total cross section and $\rho$-parameter at asymptotic energies in proton-proton ($pp$) and antiproton-proton ($\bar{p}p$) collisions. For this intent, we consider three of the main theoretical results in high energy physics: the crossing property, the derivative dispersion relation, and the optical theorem. The use of such machinery allows the analytic formulas for wide set of the measured global scattering parameters and some important relations between them. The suggested parameterizations approximate simultaneously the energy dependence for total cross section and $\rho$-parameter for $pp$ and $\bar{p}p$ with statistically acceptable quality in multi-TeV region. Also the qualitative description is obtained for important interrelations, namely difference, sum and ratio of the antiparticle-particle and particle-particle total cross sections. Despite the reduced number of experimental data for the total cross section and $\rho$-parameter in TeV-scale, which turns any prediction for the beginning of the asymptotic domain a hard task, the fitting procedures indicates that asymptotia lies in the energy range 25.5-130 TeV. Moreover, in the asymptotic regime, one obtains $\alpha_{\mathbb{P}}=1$. Detailed quantitative study of energy behavior of measured scattering parameters and their combinations in ultra-high energy domain indicates that the scenario with the generalized formulation of the Pomeranchuk theorem is more favorable with respect to the original formulation of this theorem., Comment: 22 pages, 5 figures and 7 tables

In this work, the distance between a quark-antiquark pair is analyzed through both the confinement potential as well as the hadronic total cross section. Using the Helmholtz free energy, entropy is calculated near the minimum of the total cross section through the confinement potential. A fitting procedure for the proton-proton total cross section is performed, defining the fitting parameters. Therefore, the only free parameter remaining in the model is the mass scale $\kappa$ used to define the running coupling constant of the light-front approach to QCD. The mass scale controls the distance $r$ between the quark-antiquark pair and, under some conditions, it allows the occurrence of free quarks even in the confinement regime of QCD., Comment: 16 pages, 2 figures. This improved version contains corrections for some typos as well as some development in discussions along the text

In this paper, one uses a damped potential to present a description of the running coupling constant of QCD in the confinement phase. Based on a phenomenological perspective for the Debye screening length, one compares the running coupling obtained here with both the Brodsky-de T\'eramond-Deur and the Richardson approaches. The results seem to indicate the model introduced here corroborate the Richardson approach. Moreover, the Debye screening mass in the confinement phase depends on a small parameter, which tends to vanish in the non-confinement phase of QCD., Comment: Minor misprints corrected. Accepted for publication in Int. J. Mod. Phys. A36, 2150084 (2021)

Based on the Pomeranchuk theorem, one constructs the $\delta(s)$ parameter to measure the difference between experimental data for the particle-particle and particle-antiparticle total cross section at the same energy. The experimental data for the proton-proton and proton-antiproton total cross section were used to show that, at the same energy, this parameter tends to zero as the collision energy grows. Furthermore, one assumes a classical description of the total cross section, dividing it into a finite number of non-interacting disjoint cells, each one containing a quark-antiquark pair subject to the confinement potential. Near the minimum of the total cross section, one associates $\delta(s)$ with the entropy generated by these cells, analogous to the XY model. Using both the Quigg-Rosner and Cornell confinement potentials and neglecting other energy contributions, one can calculate the internal energy of the hadron. One obtains that both the entropy and internal energy possess the same logarithmic dependence on the spatial separation between the pairs in the cell. The Helmholtz free energy is used to estimate the transition temperature, which is far from the temperature widely related to the Quark-Gluon Plasma., Comment: Change in the title and minor changes along the text. Final version accepted for publication in Mod. Phys. Lett. A

In this paper, one discusses the effects of the Tsallis entropy on the radial pressure distribution in the proton. Using a damped confinement potential the pressure distribution is obtained from the Tsallis entropy approach, being the entropic-index $\omega$ connected with the proton temperature concerning some transition temperature. Then, the approach allows the study of the proton thermal evolution up to the Quark-Gluon Plasma regime. The von Laue stability condition, arising from the pressure distribution results in positive and negative energy regions. An analogy between the results for the radial pressure distribution and the proton-proton and the antiproton-proton total cross section is performed. The negative energy region is identified with the odderon exchange while the positive represents the pomeron exchange dominance above some transition energy $\sqrt{s_c}$. The hollowness effect is also discussed in terms of the results obtained and the proposed analogy., Comment: 11 pages and 4 figures

This work presents the subtraction procedure and the Regge cut in the logarithmic Regge pole approach. The subtraction mechanism leads to the same asymptotic behavior as previously obtained in the non-subtraction case. The Regge cut, on the other hand, introduces a clear role to the non-leading contributions for the asymptotic behavior of the total cross section. From these results, one introduces some simple parameterization to fit the experimental data for the proton-proton and antiproton-proton total cross section above some minimum value up to the cosmic-ray. The fit parameters obtained are used to present predictions for the $\rho(s)$-parameter as well as to the elastic slope $B(s)$ at high energies., Comment: Accepted for publication in Chinese Physics C

Neglecting spin effects, one introduces here a subtle approximation for the scattering angle, which allows the obtaining of a logarithmic leading Regge pole, consistent with the Froissart-Martin bound. A simple parameterization is also introduced for the proton-proton total cross section. Fitting procedures are implemented only for the highest energy experimental data available. The intercept for a linear approach is obtained, indicating the presence of a soft pomeron. The Tsallis entropy in the impact parameter space is calculated using the Regge pole formalism. This entropy depends on a free parameter, whose value implies the existence of a central or non-central maximum value for the entropy. The hollowness effect is discussed in terms of this parameter., Comment: Accepted for publication in the Physica Scripta

In this work, one proposes the use of a damped confinement potential to mimic the proton internal energy. The internal pressure is calculated taking into account the occurrence of a phase transition in the $pp$ and $\bar{p}p$ total cross section. The model predicts the inversion of the positive and negative pressure regions depending on the squared energy $s_0$, where the total cross section achieves its minimum value. Considering energies below the phase transition the expected results are in accordance with the recent proton internal pressure measurement. For energies above $s_0$, the model predicts a negative pressure region near the center of the hadron surrounded by a positive pressure region., Comment: A version of this paper was accepted for publication in the International Journal of Modern Physics A

This work reports the production and characterization of lithium-loaded liquid scintillator (LiLS) for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). Fifty-nine 90 liter batches of LiLS (${}^6{\rm Li}$ mass fraction 0.082%$\pm$0.001%) were produced and samples from all batches were characterized by measuring their optical absorbance relative to air, light yield relative to a pure liquid scintillator reference, and pulse shape discrimination capability. Fifty-seven batches passed the quality assurance criteria and were used for the PROSPECT experiment., Comment: 16 pages, 15 figures

In this paper, one uses the Tsallis entropy in the impact parameter space to study $pp$ and $\bar{p}p$ inelastic overlap function and the energy density filling up mechanism responsible by the so-called black disk limit as the energy increases. The Tsallis entropy is non-additive and non-extensive and these features are of fundamental importance since the internal constituents of $pp$ and $\bar{p}p$ are strongly correlated and also the existence of the multifractal character of the total cross-section. The entropy approach presented here takes into account a phase transition occurring inside the hadrons as the energy increases. This phase transition in the impact parameter space is quite similar to the Berezinskii-Kosterlitz-Thouless phase transition, possessing also a topological feature due to the multifractal dimension of the total cross-sections in $pp$ and $\bar{p}p$ scattering., Comment: 18 pages, 6 figures

This paper presents a qualitative explanation for the hollowness effect based on the inelastic overlap function, claiming this result is a consequence of fundamental thermodynamic processes. Using the Tsallis entropy, one identifies the entropic index $w$ with the ratio of the collision energy to critical one in the total cross-section. The integrated probability density function is replaced by the inelastic overlap function, which represents the probability of occurrence of an inelastic event depending on both the collision energy and impact parameter. The Coulomb potential, as well as the confinement potential, are used as naive approaches to describe the (internal) energy of the colliding hadrons. The Coulomb potential in the impact parameter picture is not able to furnish any reliable physical result near the forward direction. However, the confinement potential in the impact parameter space results in the hollowness effect shown by the inelastic overlap function near the forward direction., Comment: 25 pages, 12 figures, 2 tables

In a previous work a novel parametrization was proposed for the $pp$ and $\bar{p}p$ total cross section. Here, results are presented for analysis updated with taken into account the recent data from accelerator experiments as well as from cosmic ray measurements. The analytic parameterizations suggested within axiomatic quantum field theory (AQFT) provide the quantitative description of energy dependence of global scattering observables with robust values of fit parameters. Based on the fit results the estimations are derived for the total cross section and the $\rho$ parameter in elastic $pp$ scattering at various $\sqrt{s}$ up to energy frontier $\sqrt{s}=10$ PeV which can be useful for present and future hadron colliders as well as for cosmic ray measurements at ultra-high energies., Comment: 10 pages, 2 figures and 3 tables

In this paper one presents a naive parametrization to $pp$ and $\bar{p}p$ total cross sections. The main goal of this parametrization is to study the possible fractal structure present in the total cross section. The result of the fitting procedure shows two different fractal dimensions: a negative (low-energies) and a positive (high-energies). The negative fractal dimension represents the emptiness of the total cross section structure and the positive represents the filling up process with the energy increase. Hence, the total cross section presents a multifractal behavior. At low-energies, the odderon exchange may be associated with the negative fractal dimension and at high-energies, the pomeron may be associated with the positive fractal dimension. Therefore, the exchange of odderons and pomerons may be viewed as a transition from a less well-defined to a more well-defined internal structure, depending on the energy., Comment: 8 pages, 3 figures

We use an almost model-independent analytical parameterization for $pp$ and $\bar{p}p$ elastic scattering data to analyze the eikonal, profile, and inelastic overlap functions in the impact parameter space. Error propagation in the fit parameters allows estimations of uncertainty regions, improving the geometrical description of the hadron-hadron interaction. Several predictions are shown and, in particular, the prediction for $pp$ inelastic overlap function at $\sqrt{s}=14$ TeV shows the saturation of the Froissart-Martin bound at LHC energies., Comment: 15 pages, 16 figures

Considering the Froissart-Martin bound, Jin-Martin-Cornille bound and the optical theorem, we propose a novel parametrization for the total cross-section of proton-proton and antiproton-proton elastic scattering data. Using derivative dispersion relations we obtain the real part of the elastic scattering amplitude and thus the $\rho$ parameter. Simultaneous fits to $\sigma_{tot}$ and $\rho$ are performed allowing very good statistical descriptions of the available data. Furthermore, predictions to $\sigma_{tot}$ and $\rho$ at energies not used in the fit procedures are presented. For $\sigma_{tot}$ we obtain predictions at RHIC, LHC and future HC energies., Comment: 22 pages, 7 figures and 11 tables. We corrected some formulas and results of the fitting procedure. This work present intermediate steps and results that are not shown in the published version

Using a Lagrangean toy model the coupling of a negative pion superconducting field and the electromagnetic field of the star is analyzed. A numerical study of particles produced in the neutron star medium by means of the well-known parametric resonance phenomenon is performed., Comment: 7 pages,5 figures, revtex format

Based on the behavior of the elastic scattering data, we introduce an almost model-independent parametrization for the imaginary part of the scattering amplitude, with the energy and momentum transfer dependences inferred on empirical basis and selected by rigorous theorems and bounds from axiomatic quantum field theory. The corresponding real part is analytically evaluated by means of dispersion relations, allowing connections between particle-particle and particle-antiparticle scattering. Simultaneous fits to proton-proton and antiproton-proton experimental data in the forward direction and also including data beyond the forward direction, lead to a predictive formalism in both energy and momentum transfer. We compare our extrapolations with predictions from some popular models and discuss the applicability of the results in the normalization of elastic rates that can be extracted from present and future accelerator experiments (Tevatron, RHIC and LHC)., Comment: 17 pages, 17 figures, to appear in Eur. Phys. J. C

In this work we propose a new mechanism for photoproduction inside a neutron star based on Parametric Resonance phenomenon as firstly applied to Inflationary Cosmology. Our assumptions are based on the pion condensation model by Harrington and Shepard. We show that a huge number of photons are created which, on turns, reheats the matter in the star's core. Thus, we argue that Parametric Resonance can be effective during a brief period out of an neutron star lifetime leading to an anomalous uprising variation of its brightness departing from the black body radiation at regularly spaced frequencies. In adition, a time periodic signal is obtained in moderate (not exponential) regimes. We argue also that our PR mechanism offers a simple and feasible explanation for some recent observations of giant flares from neutron stars., Comment: 15 pages, 8 figures. Submitted to Phys. Rev. D