Two equations whose variables take values in the Pauli algebra of complex quaternions are shown to be equivalent to the standard Dirac equation and its Hermitian conjugate, taken together. They are transformed one into the other by an outer automorphism of the Pauli algebra. Given a solution to the Dirac equation, a new solution is obtained by multiplying it on the right by one of the 16 matrices of the Pauli group. This defines a homomorphism from the Pauli group into the group of discrete symmetries, whose kernel is a cyclic group of order four. The group of discrete symmetries is shown to be the Klein four-group consisting of four elements: the identity Id; the charge conjugation symmetry C; the mass inversion symmetry M; and their composition in either order, CM=MC. The mass inversion symmetry inverts the sign of the mass leaving the electric charge unchanged.

Accurate flux measurement of low energy charged particles, trapped in the magnetosphere, is necessary for Space Weather characterization and to study the coupling between the lithosphere and magnetosphere, allowing the investigation of the correlations between seismic events and particle precipitation from Van Allen Belts. In this presentation, the project of a CubeSat space spectrometer, the Low Energy Module (LEM) is shown. The detector will be able to perform an event-based measurement of energy, direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows photon detection in the sub-MeV range, joining the quest for the investigation of the nature of Gamma Ray Bursts.

The particle identification of the LEM relies on the ∆E−E technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10x10x10 cm3 CubeSat frame and it will be constructed as a joining project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements an innovative approach, based on active particle collimation, was designed for the LEM, this avoids heavy/bulky passive collimators of previous space detectors. In this talk, we will present the LEM geometry, its detection concept, and the results from the developed GEANT4 simulation. Also, the results from the characterisation of LEM silicon detectors in the INFN-TIFPA laboratory will be presented.

Neutrinoless double beta decay is one of the pillars in the search for Physics beyond the Standard Model, this process allows to exploit the characteristics decay Q-value for a possible identification of the Majorana nature of the neutrinos and Leptonic quantum number violation.

The Seesaw models provide a compelling mechanism to naturally generate the small neutrino mass, moreover both the problem of baryon asymmetry in the Universe and different Dark Matter (DM) candidates, can be addressed by these models.

Among the DM candidates, beyond the case of a possible scalar majoron, also a Majorana fermion candidate, the sterile neutrino, is expected.

Focusing on the Majorana fermion DM candidates, the expected interactions are dominated by the L-violating vertex coupling to the majoron, thus the direct detection of such a DM scattering on charged fermions is suppressed.

In this work the diagram responsible for the expected neutrinoless double beta decay will be considered for the possible detection technique of a Majorana fermion DM inelastically scattering on a double beta unstable nucleus, stimulating its decay.

In particular the exothermic nature of the stimulated double beta decay would allow the direct detection also of a light DM fermion, a class of DM candidates that are difficult/impossible to investigate with the traditional elastic scattering techniques.

In this work we avoid studying the details of a specific interaction model, since beyond the sterile neutrino also other popular DM candidates are expected to be Majorana fermions (like, e.g., the supersymmetric Neutralino, Axino and Gravitino) and we will focus on the phenomenology of this novel detection technique.

The expected signal distribution for different DM masses, as in the case of a possible 7.1 keV sterile neutrino and the upper limits on the nucleus scattering cross sections, based on the current experimental data, will be discussed.

We investigate the Friedmann-Lemaitre-Robertson-Walker (FLRW)

cosmological models within the framework of Rastall gravity incorporating

particle creation. The modified field equations for Rastall gravity are

derived and exact solutions are obtained under various assumptions of the

scale factor. The qualitative behaviour of our solutions depends on the

Rastall coupling parameter ψ = kλ. Following Akarsu et al. 2020 [Eur.

Phys. J. C 80, 1050], we have restricted the Rastall coupling parameter

ψ (k = 1) to the range -0.0001 < ψ < 0.0007 at 68% CL from CMB+BAO

data. Further, we have discussed the distinct physical behaviour of the

derived models in detail.

In the recent work, the hairy Vaidya black hole solution has been obtained by using the gravitational decoupling method. We derive a hairy black hole solution if we assume the existence of a new matter field which can be associated with dark matter. If we consider the gravitational collapse of the matter cloud, described by the new solution, then the result might be a regular (non-singular) black hole. We introduce the regularity conditions and find out how dark matter affects the formation of a regular black hole.

Introduction: Stellar evolution is predominantly governed by the mass of the star. Depending upon the mass, stars take different trajectories from their Main Sequence (MS) period to their death. In our work, we are particularly interested in the MS stars with masses ranging from 140M⊙ to 240M⊙ as they die in the process of Pair Instability Supernova (PISN) leaving no remnant post explosion. Thus, Standard Stellar theory forbids the formation of black holes within the mass range of 60M⊙ to 130M⊙ due to PISN, creating a gap in the black hole mass function. But in 2019, LIGO & Virgo detected a binary black hole merger (GW190521) of two black holes with masses of 85M⊙ and 66M⊙, merging into a single black hole of mass 150M⊙. The observational evidence of GW190521 does not comply with the existing theory. Hence, we propose a new insight for the existence of the black holes in the Pair-Instability mass gap region.

Method: Weakly Interacting Massive Particles (WIMPs) are hypothesized to be Dark Matter (DM) particles which the are thermal relics of the early universe and interact normally only via gravity. Cosmological models suggest the likelihood of first stars being the Massive Population III stars that may have exploded as PISN and Pulsational PISN. As the presence of DM particles were denser at the earlier epochs, it would be more likely for massive stars to accumulate DM particles. The presence of DM, even in a small fraction, admixed with baryonic matter can affect the stellar structure and evolution of the progenitor of PISN. Using the relation between the mass and parameters like temperature, lifetime, and luminosity we have analyzed how DM particles of different mass can affect the progenitor of PISN for different fractions.

Result: Higher the fraction of DM admixture, higher will be the temperature and luminosity in order to maintain the equilibrium. The increased temperature and luminosity will cause the lifetime of the PISN progenitor to drop to around half, even in the presence of relatively small fractions of DM. Even 10% of DM particles with a mass of 50 GeV is sufficient to rise the temperature by a factor of 10. Thereby, allowing the progenitor to escape the PISN stage by overcoming the explosive oxygen phase and collapsing into a black hole. The respective calculations and graphs leading to this conclusion have been mentioned in the paper elaborately.

Summary: We have looked upon the effects of DM in the progenitors of PISN in terms of luminosity, lifetime and temperature and show that with DM admixture, the progenitors can avoid the PISN stage, to collapse into a black hole.

We studied scalar field φCDM models: ten quintessence models and seven phantom models. We reconstructed these models, using the phenomenological method developed by us. Resulting in, for each potential the following ranges were found: (i) model parameters; (ii) EoS parametelarge-scale structure of the universers; (iii) initial conditions for differential equations, which describe the dynamics of the universe. Using the MCMC analysis, we obtained constraints on scalar field models by comparing observations for: the expansion rate of the universe, the angular diameter distance and the growth rate function with corresponding data generated for the fiducial ΛCDM model. We applied the Bayes statistical criteria to compare scalar field models. To this end, we calculated the Bayes factor, as well as the AIC and BIC information criteria. The results of this analysis showed that we could not uniquely identify the preferable scalar field φCDM models compared to the fiducial ΛCDM model based on the predicted DESI data, and that the ΛCDM model is a true dark energy model. We investigated scalar field φCDM models in the w₀ - w_a phase space of CPL- ΛCDM contours. We identified subclasses of quintessence and phantom scalar field models, which at the present epoch: (i) can be distinguished from the ΛCDM model; (ii) cannot be distinguished from the ΛCDM model; (iii) can be either distinguished or undistinguished from the ΛCDM model. We found that all studied models can be divided into two classes: models that have attractor solutions and models whose evolution depends on initial conditions

In this paper, we investigated the four classical tests of general relativity in the non-commutative (NC) gauge theory of gravity, using the Seiberg-Witten (SW) map and the star product, we calculate the deformed metric components ĝ_µν (r, Θ) of the Schwarzschild black hole. This deformed metric enables us to calculate the gravitational periastron advance of mercury, red-shift, deflection, and time delay of light in this NC spacetime. Our results for NC prediction of the gravitational deflection and time delay of light show a new behavior than the classical one. As an application, we use a typical primordial black hole to give an estimation to the NC parameter Θ, where our result shows Θ^phy ∼ 10 ⁻²¹ m for the gravitational red-shift, deflection, and time delay of light at the final stage of inflation, and Θ^phy ∼ 10 ⁻³¹ m for the gravitational periastron advance for some planets of our system solar.

The locally rotationally symmetric Bianchi type-I cosmological models are explored both in general relativity and in an alternative modified theory of gravity, viz., f(R, T) gravity. Solutions have been found by assuming a special form for the Hubble parameter, which results in a hyperbolic hybrid scale factor. The geometrical features of the model, including the jerk parameter, have been discussed. In order to ensure the viability of the solutions, various constraints have been imposed. A comparison is made between the solutions in general relativity and in f(R, T) gravity. It is found that both the solutions in general relativity and in f(R, T) gravity possess very rich behaviour. In general relativity and in f(R, T) gravity, the equation of state permits a transition from normal (stiff) matter to quintessence, phantom, and then later to a solution that mimics the cosmological constant, depending on the values of m, n, Q and lambda  (the various parameters of the solutions). Our results are illustrated throughout by means of relevant diagrams. It is found that in general, the solutions exhibit late-time acceleration both in general relativity as well as in f(R, T) gravity.

The recent Planck Legacy 2018 release verified the presence of an enhanced lensing amplitude in the power spectra of the cosmic microwave background with a confidence level of over 99%, which implies that the early Universe had a positive curvature. In this study, the curvature of the early Universe is regarded as the curvature of 4D conformal bulk while celestial objects that induce a localized curvature in the bulk are considered as 4D relativistic cloud-worlds. Likewise, quantum fields are considered as 4D relativistic quantum clouds that are affected by the curvature of the bulk as a manifestation of gravity. This approach could eliminate the singularities and satisfy the conditions of a conformal invariance theory.