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  • Open access
  • 33 Reads
Dark atom solution for the puzzles of direct dark matter search
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

The puzzle of direct dark matter searches can find solution in the model of OHe dark atom, which consists of a stable O-- lepton core and nuclear interacting (alpha particle) shell of primordial helium nuclei. In this model positive results of DAMA group can be explained by annual modulation of radiative capture of OHe atoms to low-energy bound states with sodium nuclei, which doesn’t take place under the conditions of other underground experiments. The existence of such a low-energy bound state is the key problem of the OHe model of composite dark matter. The complexity of this problem, which has not found a correct solution during last 15 years, requires a consistent approach to its solution. Within the framework of the proposed approach to such modeling, in order to reveal the essence of the processes of interaction of OHe with the nuclei of baryonic matter, a classical model is used, to which the effects of quantum physics and final size of nuclei are successively added. The numerical model of the interaction of the “dark” OHe atom with the nuclei is developed by successive addition of realistic features of quantum-mechanical description to the initial classical problem of three point-like bodies ( O-- particle, the He nucleus and the target nucleus). The developed approach leads to a numerical model describing the OHe-nucleus system with self-consistent accounting for nuclear attraction and electromagnetic interaction of dark atom with nuclei. The model can prove the interpretation of the results of the direct underground experimental dark matter search in the terms of dark atom hypothesis.

  • Open access
  • 52 Reads
Reflecting on design principles in the context of virtual reality learning experiences in astronomy and science education

Virtual reality (VR) technologies have the potential to profoundly transform learning activities in astronomy and science through new forms of perceptual engagement and bodily participation. Since advancements in technology and education drive change in each other, researchers have started to explore opportunities and challenges of using VR in (in)formal learning environments. While research on VR from technology perspectives is extensive, there are relatively few attempts to explore learning-oriented design considerations with VR tools.

This study is grounded in the education and public-outreach program of the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav). The OzGrav-team is an interdisciplinary team of science educators, VR developers, digital artists and astrophysicists that have developed VR outreach programs and school incursions in astronomy.

The goal of this study is to identify the experiential affordances of VR in informal learning contexts and to reflect on potential design principles for VR learning experiences in astronomy and science. To articulate issues related to design and learning with VR from multiple perspectives, we unpack critical design decisions of the OzGrav VR learning resources in the form of a dialogue between VR-practitioners and educational researchers. The dialogue draws on primary data from focus-group-interviews with the OzGrav-team. We supplement the dialogue with audio-visual material of a VR experience about the virtual universe. Our findings centre on aspects of

  1. collaboration and social interaction in VR-learning,
  2. negotiating roles while being an observer/participant in the VR-experience,
  3. embodiment in an immersive VR environment,
  4. finding a balance between visual richness and accessibility of VR-experiences,
  5. limitations of what VR environments can visualize.

As the use of VR learning environments gains momentums, our findings contribute to a deeper understanding of the new learning contexts that VR technology can create in astronomy and modern science education.

  • Open access
  • 15 Reads
Fermion masses and mixing within a SU(3) family symmetry model with five sterile neutrinos
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

Within a broken local vector-like SU(3) family symmetry, we address the problem of quark masses and mixing in a framework with five sterile neutrinos.

Heavy fermions, top and bottom quarks and tau lepton become massive at tree level from See-saw mechanisms implemented by the introduction of a new set of SU(2)_L weak singlets vector-like fermions U,D,E,N, with N a neutral lepton. The fermion content also include three right handed neutrinos introduced to cancel anomalies. Therefore, in this scenario light quarks and leptons, including active neutrinos and a light O(eV) sterile neutrino, become massive from radiative loop corrections mediated by the massive SU(3) gauge bosons.

We provide a parameter space region where this framework can accommodate the known hierarchical spectrum of quark masses and mixing, the charged lepton masses and simultaneously suppress properly the current experimental constraints on Ko − \bar{Ko} and Do − \bar{Do} meson mixing.

We also report the non-unitary, (VCKM)_{4×4} and (UPMNS)_{4×8}, quark and lepton mixing matrices.

In addition, we find out that the mass of the SU(2)_L weak singlet vector-like D quark introduced in this scenario may lie within a few TeV's region, and hence within current LHC possibilities.

  • Open access
  • 27 Reads
Effects of baryon-antibaryon annihilation in the evolution of antimatter domains in baryon asymmetrical Universe
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

The mechanisms of baryosynthesis, which involve the three Sakharov's conditions, admit a possibility of nonhomogeneous generation of baryon excess. It may take place in the case of spatial variation of CP violating phase or of the baryon generating field in the early Universe. In the extreme case this nonhomogeneity can lead to the change of sign of baryon excess and formation of antibaryon domains in baryon asymmetrical Universe. Surrounded by the baryon matter, evolution of antibaryon domains is strongly influenced by effect of baryon and antibaryon diffusion to the border of domain and their annihilation. It leads to change of size of domains and antibaryon density in them. The consequence of antibaryon-baryon annihilation at the border of antimatter domains in baryon-asymmetrical Universe is investigated. The successive evolution in the expanding Universe strongly depends on antibaryon density within domain. At low density it is not sufficient to provide separation from cosmological expansion. Such separation can, however, be provided by effects of dark matter, which we briefly discuss. Low-density antimatter domains are further classified with the account for the border interactions. Differently, a similar classification scheme is also proposed for higher-densities antimatter domains. Antimatter domains containing antiprotons and different types of antinuclei are also analyzed within the framework of non-trivial baryosynthesis processes. The antiproton-proton annihilation interactions are therefore schematized and evaluated. The effects of antinuclei-nuclei-interaction-patterns are investigated and taken into account in the analysis of antimatter domain evolution.

  • Open access
  • 38 Reads
Inflation, primordial black holes and induced gravitational waves from modified supergravity
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

Modified (Starobinsky type) supergravity is used for a viable (unified) description of cosmological inflation and formation of primordial black holes and dark matter in the early Universe. A specific class of models is proposed and investigated in detail. Their observational predictions for primordial black hole masses, dark matter and induced gravitational waves are derived and compared to the current and future astrophysical and cosmological observations. Our approach naturally leads to the two-scalar-field attractor-type double inflation, whose first stage is driven by Starobinsky scalaron and whose second stage is driven by another scalar field which belongs to a supergravity multiplet. The scalar potential and the kinetic terms are derived, the vacua are studied, and the inflationary dynamics of those two scalars is investigated. We numerically compute the power spectra and find the ultra-slow-roll regime leading to an enhancement (peak) in the scalar power spectrum. This leads to an efficient formation of primordial black holes. We estimate their masses and find their density fraction as part of dark matter. We show that our modified supergravity models are in agreement with inflationary observables, while they predict the primordial black holes masses in the range between 10^16 g and 10^20 g. In this sense, modified supergravity provides a natural top-down approach for explaining and unifying the origin of inflation and the dark matter in the form of primordial black holes.

  • Open access
  • 57 Reads
Balancing asymmetric dark matter with baryon asymmetry by sphaleron transitions
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

The effect of the electroweak sphaleron transition in balance between baryon excess and and the excess of stable quarks of $4^{th}$ generation is studied in this paper. Considering the non-violation of $SU(2)$ symmetry and the conservation of electroweak and new charges and quantum numbers of the new family, it makes possible sphaleron transitions between baryons, leptons and 4th family of leptons and quarks. In this paper we have tried to established a possible definite relationship between the value and sign of the $4^{th}$ family excess relative to baryon asymmetry. If $U$-type quarks are the lightest quarks of the $4^{th}$ family and sphaleron transitions provide excessive $\bar U$ antiquarks,
asymmetric dark matter in the form of dark atom bound state of ($\bar U \bar U \bar U$) with primordial He nuclei is balanced with baryon asymmetry.

The main scope of our current activity is to deduce the relationship between baryon excess and excess of stable fermions of $4^{th}$ family. We can take for definiteness that $4^{th}$ neutrino and U-quark of $4^{th}$ family are stable and establish the relationship between their excess and excess of baryons and leptons by sphaleron transitions. The aim is to find conditions at which observed baryon excess corresponds to such an excess of $\bar{U}$ that explains observed dark matter by $(\bar{U} \bar{U} \bar{U})He$ atoms.

  • Open access
  • 35 Reads
Solar System Peculiar Motion from Mid Infra Red Quasars and Implications for the Cosmological Principle
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

According to the cosmological principle, the universe should appear isotropic, without any preferred directions, to a comoving observer. However a peculiar motion of the observer, or equivalently of the solar system, might introduce a dipole anisotropy in the observed properties of a class of objects. The peculiar motion of the solar system, determined from the Cosmic Microwave Background Radiation (CMBR), gave a velocity 370 km /s along l=264, b=48 deg. Dipoles subsequently observed in the number counts, sky brightness or redshift distributions in large samples of distant radio galaxies and quasars have yielded peculiar velocities many times larger than that from the CMBR, though in all cases the directions matched with the CMBR dipole. We have now determined our peculiar motion from the MIRAGN (Mid Infra Red Active Galactic Nuclei) sample of more than a million quasars, originally drawn from the CATAWISE survey of more than a billion objects. We find a peculiar velocity more than an order of magnitude higher than the CMBR value, although the direction seems within 1.2 sigma of the CMBR dipole. Since a genuine solar peculiar velocity cannot vary from one dataset to the other, an order of magnitude, statistically significant, discordant dipoles, could imply that we may instead have to look for some other cause for the genesis of these dipole, including that of the CMBR. A common direction for all these dipoles, determined from completely independent surveys by different groups, does indicate that these dipoles are not merely due to some systematics in the observations or in the data analysis, and it might suggest a preferred direction in the universe implying an inherent anisotropy, which, in turn, would violate the cosmological principle, a cornerstone of the modern cosmology.

  • Open access
  • 19 Reads
Multimessenger probes for new physics in the light of A.Sakharov's legacy in cosmoparticle physics
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session The Universe of Andrei Sakharov

The modern Standard cosmological scenario, reflecting to large extent the development of A.D.Sakharov’s legacy in cosmoparticle physics, involves inflation, baryosynthesis and dark matter/energy. Physics of all these elements of the cosmological paradigm lays Beyond the Standard model (BSM) of elementary particles and involves in its turn cosmological probes for its study. To specify this physics the idea of multi-messenger probes of new physics is proposed, involving the set of additional model dependent consequences of physical models for inflation, baryosynthesis and dark matter. After brief review of Cosmophenomenology of new physics, we concentrate on probes for mechanisms of baryosynthesis, first proposed by A.D.Sakharov, which are of special interest in this context. Antimatter domains formed in the early Universe can reflect possible strong nonhomogeneity of baryosyntehsis. In homogeneous and isotropic Universe such nonhomgeneity is determined by specific model dependent choice of mechanisms of inflation and baryosynthesis. These mechanisms are beyond the standard model of elementary particles and provide tests for the physics, underlying the modern cosmology. Constraints on macroscopic antimatter objects or cosmic fuxes of antinuclei provide probes for the corresponding models. Positive evidence for maroscopic antimatter existence leads beyond the standard paradigm of the cosmological scenario and specify with high precision the parameters of BSM physics .

  • Open access
  • 25 Reads
New perspectives for multifrequency GW astronomy: strong gravitational lensing of GW
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session Deep-Space Probes

Direct detection of gravitational waves was for a long time a holy grail of observational astronomy. The situation changed several years ago with the first ever laboratory detection of gravitational wave signal on the Earth (GW150914), showing once again that Einstein was right. Now, successful operating runs of LIGO/Virgo gravitational wave detectors, resulting with numerous detections of gravitational wave signals from coalescing double compact objects (mainly binary black hole mergers) with the first evidence of coalescing binary neutron star system, elevated multimessenger astronomy to the unprecedented stage. Double compact objects (binary black hole systems, mixed black hole-neutron star systems and double neutron star systems) are the main targets of future ground based and space-borne gravitational wave detectors opening the possibility for multifrequency gravitational wave studies and yielding very rich statistics of such sources. This, in turn, makes possible that certain, non-negligible amount of double compact objects will have a chance of being strongly lensed. In this presentation I will discuss new perspectives for future detections of gravitational wave signals in the case of strong gravitational lensing. First, the expected rates of lensed gravitational wave signals will be presented. Multifrequency detections of lensed gravitational wave events, will demand different treatment at different frequencies, i.e. wave approach vs. geometric optics approach. I will discuss new possibilities emerging from such multifrequency detections.

  • Open access
  • 24 Reads
Beryllium radioactive isotopes as a probe to measure residence time of Cosmic Rays in the Galaxy and halo thickness.
Published: 22 February 2021 by MDPI in 1st Electronic Conference on Universe session Deep-Space Probes

Cosmic Rays (CR) are a powerful tool for the investigation of the structure of the magnetic fields in the galactic halo and the property of the Inter-Stellar Medium. In particular the ratio of secondary CR (as Li,Be,B) over the primary CR (as He,C,O) is able to provide the grammage, that is the amount of material crossed by CR in their journey through the Galaxy. Two parameters of the CR propagation models: the galactic halo thickness, H, and the diffusion coefficient, D, are loosely constrained by such a grammage measurement, in particular a large degeneracy exist being only H/D well measured. The uncertainties on D and H parameters (this last one know to be in the range 3-8 kpc) also reflects on the accuracy of the determination of secondary anti-proton and positrons fluxes that are the background for the Dark Matter or exotic (astro-)physics searches. The 10Be/9Be isotopic flux ratio (thanks to the 2 My lifetime of 10Be) can be used as a radioactive clock providing the measurement of CR residence time in the galaxy. This is an important tool to solve the H/D degeneracy. Past measurements of 10Be/9Be isotopic flux ratio in CR are scarce, limited to low energy and affected by large uncertainties. Here a new technique to measure 10Be/9Be isotopic flux ratio with a Data-Driven approach in magnetic spectrometers is presented. As an example by applying the method to Beryllium data collected and published by PAMELA collaboration it is now possible to determine this important measurement avoiding the prohibitive uncertainties coming from the Monte Carlo simulation. It is shown that the accuracy of PAMELA data permits to infer a value of the halo thickness H within 20% precision.