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  • 34 Reads
Introduction to a “radical” working hypothesis about a hemisphere-scale impact on Dione (Saturn)
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Space and Planetary Sciences

The suspected and proved existence of subsurface oceans on various icy satellites of gas and ice giants such as Callisto, Europa, and Ganymede (Jupiter), Dione, Enceladus and Titan (Saturn), and Triton (Neptune), and the potential that such oceans may harbour life, triggered the renaissance of the research of those planetary bodies (including the ongoing Europa Clipper and JUICE missions). The centre of our research is Dione and its surface characteristics, especially with the focus on the possible relationship between the distribution of certain size craters, linear features and resurfacing processes. The pivot of the study is the region, located westward from the Eurotas and Palatine chasmata spreading approximately between latitude 50° and -50° and longitude -100° to 60° (positive East), roughly at the “transitional hemisphere” between the trailing and leading hemisphere of the moon. The studied area is defined as Intermediate Cratered Terrain, and referred as a region, which was resurfaced at some point during the early history of Dione by a still unknown process, which erased some early generation craters. This study introduces a “radical” working theory about a giant, most likely low-angle impact on the surface of Dione around 4 Ga ago, contributing to the resurfacing of the terrain. Such impact might result in the asymmetrical (“half-ring like”) distribution of secondary craters, observed in the area (i), and the formation of some early component of the Fault Terrain by the dilatation stress field during the modification phase of the impact, and/or later, during the isostatic relaxation of the surface (ii). Along surficial features, the possible formation of a unique Saturn-orbiting impactor population out of the ejectiles (or alternatively, as a “chicken and egg problem”, they might be the source of the impactor) (iii), and the very theoretical formation of the Trojan moon Helene (Dione B) following the accretion of the ejectiles (iv), might be also the results of the hemisphere-scale impact.

  • Open access
  • 290 Reads
Entanglement --- a higher order symmetry

On October 4, 2022, the Nobel prize for physics was awarded to Alain Aspect, John Clauser and Anton Zeilinger for their experimental work related to quantum entanglement, a controversial topic dating back to a famous research paper published in 1935 by Einstein, Podolsky and Rosen (EPR). Elementary particles sometimes form entangled pairs. For example, two electrons in a singlet state have equal and opposite spin values if placed in a magnetic field, resulting in a sum of zero angular momentum. Consequently, if we were to model these paired electrons on the computer, we might be tempted to imagine two spheres rotating in opposite directions along a fixed axis analogous to the Earth's daily motion. However, we cannot consider elementary particles in this way since there is no fixed axis and their motion cannot be cloned. The axes change as the direction of the magnetic field change. When the spin of each entangled particle is measured in an arbitrary direction, we discover that they have equal and opposite values but until the experiment is carried out there is no preferred spin axis. In contrast to Einstein’s notion of locality, the work of Aspect, Clauser and Zeilinger motivated by Bell’s inequality suggests that quantum entanglement violates “locality.” Unfortunately, for many authors, “non-locality” has come to mean that there is “action at a distance” and that communication is faster than the speed of light. I would like to offer an alternative approach in which “non-locality” neither means faster than light communication nor does it mean that there are hidden parameters in Einstein’s sense. It will be shown that EPR entangled states constitute a higher order symmetry that are SL(2,C) invariant (and hence Lorentz invariant) and that the Pauli Exclusion Principle is a consequence of this new approach to entanglement.

  • Open access
  • 36 Reads
Supersymmetryc AdS solitons, ground states and phase transitions in maximal gauged supergravity
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Field Theory

We present new soliton solutions in a class of four-dimensional supergravity theories. For special values of the parameters, the solutions can be embedded in the gauged maximal N=8 theory and uplifted in the higher-dimensional D=11 theory. We also find BPS soliton configurations, preserving a certain fraction of supersymmetry.

Solitons play a special role in classical physics as well as in quantum and string theory, determining a richer structure of the full non-perturbative regime. This different class of exact solutions can be obtained from a double Wick rotation of a former black hole configuration, the new solutions characterizing a regular spacetime configuration devoid of horizons.
In non-supersymmetric AdS gravity, solitons play a fundamental role as they can be treated as ground states for suitable field theories. The negative mass of the AdS soliton has a natural interpretation as the Casimir energy of gauge theory living on the conformal boundary. In a non-susy version of the AdS/CFT conjecture, this would indicate that the soliton is the lowest energy solution with the chosen boundary conditions, leading to a new kind of positive energy conjecture.
Finally, BPS gravitational solitons preserving a certain fraction of supersymmetry can be found, providing a privileged framework in studying the system evolution: the resulting dynamical equations are in fact typically first-order, as compared to the standard second order equations of motion.

  • Open access
  • 41 Reads
Cold Dark Matter and Leptogenesis in the SE$_6$SSM
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Gravitation and Cosmology

In the $E_6$ inspired extension of the minimal supersymmetric (SUSY) standard model (MSSM) with an extra $U(1)_{N}$ gauge symmetry under
which right-handed neutrinos have zero charge, a single discrete $\tilde{Z}^{H}_2$ symmetry permits suppressing rapid proton decay and non-diagonal flavour transitions. To ensure anomaly cancellation this SUSY model (SE$_6$SSM) must include additional exotic matter beyond the MSSM.
If matter parity and $\tilde{Z}^{H}_2$ symmetry are preserved the SE$_6$SSM may involve two dark matter candidates. Here we consider the modification of the SE$_6$SSM in which the cold dark matter is composed of the lightest neutral exotic fermion and gravitino with mass $m_{3/2}\lesssim 1\,\mbox{GeV}$. When the sparticle mass scale lies beyond the multi-TeV range the phenomenologically acceptable density of the dark matter can be obtained in this case only for relatively low reheating temperatures $T_R\lesssim 10^{6-7}\,\mbox{GeV}$. Within this scenario the appropriate amount of the baryon asymmetry can be induced via the decays of the lightest right-handed neutrino/sneutrino into exotic states.
In general, the spin-independent part of the dark matter-nucleon scattering cross section can be much larger in the model under consideration than the corresponding experimental limit. Nevertheless we argue that there is a part of the SE$_6$SSM parameter space, in which this cross section is sufficiently strongly suppressed.

  • Open access
  • 37 Reads
Results and Prospects of the Hellenic Open University air shower array

Astroneu is an array of autonomous Extensive Air Shower detection stations deployed at the Hellenic Open University (HOU) campus on the outskirts of Patras in western Greece. In the first phase of operation 9 scintillators detectors and 3 Radio Frequency (RF) antennas have been installed and operated at the site. The detector units were arranged in three autonomous stations each consisting of three scintillator detectors (SDM) and one RF antenna. In the second phase of operation 3 more antennas were deployed at one station in order to study the correlation of the RF signals from 4 antennas subject to the same shower event. In this report we present the standard offline SDM-RF data and simulations analysis, the main research results concerning the reconstruction of the EAS parameters as well as the prospects of a new compact array that will be deployed by 2023.

  • Open access
  • 64 Reads
Majorana mass term and CAR algebra of creation and annihilation operators of Dirac and Majorana spinors
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Field Theory

We have proved that, under the standard charge conjugation approach, the Majorana mass term must vanish not only in the so called c-theory, which was known, but also in the q-theory (the theory of second quantization). In this case, the possible influence of the phase factor during charge conjugation is taken into account. It turned out that it does not affect the result.
We have derived formulas for Majorana spinor field operators without any assumptions about second quantization procedure. We have proved that the Hamiltonian of the Majorana spinor at zero momentum is zero.
The fact that the Majorana mass term and the Hamiltonian of the Majorana spinor vanish at zero momentum requires a revision of ideas about the generation of neutrino mass using the seesaw and other mechanisms.

  • Open access
  • 28 Reads
Nuclear pasta in cold non-accreting neutron stars: symmetry energy effects
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Compact Objects

The densest part of neutron-star crusts may contain very exotic nuclear configurations, so-called nuclear pasta. We investigate the effect of nuclear symmetry energy on the existence of such phases in cold non-accreting neutron stars. For this purpose, we apply four Brussel-Montreal functionals based on extended Skyrme effective interactions, which parameters were accurately calibrated to reproduce both experimental data on nuclei and realistic neutron-matter equations of state. These functionals differ in their predictions for the density dependence of the symmetry energy. Within the 4th-order extended Thomas-Fermi method, we find pasta phases occupy a larger region of the crust for models with higher symmetry energies at relevant densities in agreement with previous studies based on pure Thomas-Fermi approximation and liquid-drop models. However, the incorporation of microscopic corrections consistently calculated with the Strutinsky integral method leads to a significant shift of the onset of the pasta phases to higher densities due to the enhanced stability of spherical clusters. As a result, the pasta region shrinks significantly, and the role of symmetry energy weakens. This study sheds light on the importance of quantum effects for reliably describing pasta phases in neutron stars.

  • Open access
  • 55 Reads
Testing quantum effects of gravity and dark energy at laboratory scales
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Gravitation and Cosmology

One of the biggest challenges in modern physics is how to unify gravity with quantum theory. The current understanding of gravity is based on the general theory of relativity (in the framework of classical physics). However, this description is incomplete as quantum mechanics is considered more fundamental. Although there are several different approaches to the problem of quantizing gravity, no fully consistent theory is yet to emerge. There is an absence of a complete quantum theory of gravity, and conventionally it is thought that the effects of quantum gravity occur only at high energies (Planck scale). Here we suggest that certain novel quantum effects of gravity can become significant even at lower energies and could be tested at laboratory scales. We also suggest a few indirect effects of dark energy that can show up at laboratory scales. Using these ideas, we set observational constraints on radio recombination lines of the Rydberg atoms. This could have consequences for atomic physics, especially for large n Rydberg atoms. We also set limits on the radio recombination lines of such atoms, which are consistent with observations. We further predict that the limit of the highest n for higher Z atoms will be higher, scaling as Z(5⁄8). We further suggest that high-precision measurements of Casimir effects for smaller plate separation could also show some manifestations of the presence of dark energy.

  • Open access
  • 399 Reads

Physical Picture of Electron Spin

Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Field Theory


Pauli established the standard view that the spin of the electron was a completely abstract, non-classical angular momentum, that could not be thought of as the rotation of anything. Here we give a pedagogical presentation of old work by Belifante (1939) recently updated by Ohanian (1986) which shows that contrary to Pauli's edict, the spin of the electron can be viewed as the rotational angular momentum in the wave field of the electron.

  • Open access
  • 33 Reads
Search for exoplanets with a possible liquid surface water ocean
Published: 15 February 2023 by MDPI in 2nd Electronic Conference on Universe session Space and Planetary Sciences

Oceans and the interaction between landmasses and water were crucial driving forces during the evolution of life on Earth, so in the classical sense of habitability, it is worth searching for 'water worlds' outside our Solar System, to find possible habitats for extraterrestrial life.

Exoplanet databases proved to be valuable tools for the characterization of extrasolar systems. Some of the parameters define a certain range around the star, which determines the fate of the possible surface ocean on a planet: vanishing, evaporating, and staying in a gaseous state, or freezing and may hide under an icy crust. Thus, the term “habitable zone” was created, to define the domains around stars, where liquid water is possible to exist. Various data of 5187 confirmed exoplanets was used to find the constraints of the possibility of a global, surface water ocean.

The goal of this study was twofold: i) to apply previous models and calculations to the current database, in order to define the inner and outer edges of the circumstellar habitable zone, and ii) to characterize and classify the 239 planets, which fell into the habitable zone, regarding the appearance of the surface water ocean.

In this study, some of the parameters of the stars and the orbiting exoplanets (such as the spectral type of the system’s star, planetary mass, atmospheric composition, eccentricity, and inclination) were selected, and they were used as a proxy which may indicate a liquid surface water ocean. The selected proxies were examined with statistical tools (e.g., PCA analysis) to reveal a connection between planetary characteristics and the possible appearance of a surface ocean.