Universe, Volume 8, Issue 9 (September 2022) – 54 articles

Within the ultrarelativistic quantum molecular dynamics (UrQMD) model, the effect of initial density fluctuations on cumulants of the net-proton multiplicity distribution in Au + Au Collisions at $\sqrt{s_{NN}}$ = 7.7 GeV was investigated by varying the minimum distance $d_{\min }$ between two nucleons in the initialization. It was found that the initial density fluctuations increased with the decrease of $d_{\min }$ from 1.6 fm to 1.0 fm, and the influence of $d_{\min }$ on the magnitude of the net-proton number fluctuation in a narrow pseudorapidity window ($\Delta \eta \le$ 4) was negligible even if it indeed affected the density evolution during the collision. At a broad pseudorapidity window ($\Delta \eta \ge$ 4), the cumulant ratios were enlarged when the initial density fluctuations were increased with the smaller value of $d_{\min }$, and this enhancement was comparable to that observed in the presence of the nuclear mean-field potential. Moreover, the enhanced cumulants were more evident in collisions with a larger impact parameter. The present work demonstrates that the fingerprint of the initial density fluctuations on the cumulants in a broad pseudorapidity window is clearly visible, while it is not obvious as the pseudorapidity window becomes narrow. Full article

I review a few selected topics concerning heavy-quark fragmentation, taking particular care about bottom- and charm-quark production in $e^{+}{e}^{-}$ annihilation and the inclusion of non-perturbative corrections. In particular, I discuss the recent developments of calculations carried out in the framework of perturbative fragmentation functions and the perspective to extend them to other processes and higher accuracy. Special attention is paid to the use of an effective strong coupling constant to model hadronization effects. Full article

The cosmic microwave background (CMB) is one of the most powerful tools for cosmology. Its polarization could have imprinted the sign of an inflationary background of gravitational waves, which is supposed to have originated at ${10}^{-38}/{10}^{-35}$ seconds after the Big Bang. Detecting this background is extremely difficult because of the weakness of the signal (if any) left on the CMB polarization and because of the need to control the systematic effects. Additionally, the presence of astrophysical foregrounds, the possibility of leakage from curl-free to curl-like components, including gravitational lensing, and the instrumental noise and systematics, require sensitive detectors and smart systematic effect control. We discuss the experimental efforts spent in this field, highlighting the key observational difference and the choice that could lead, in the near future, to the detection of the curl component of the CMB polarization, a clear sign of the inflationary expansion. Full article

Many stars show activity cycles like the Sun. Kepler has gathered ∼200,000 light curves. Most of the Kepler stars only have long-cadence light curves, which limits their applicable methods. Some metrics, for example $S_{ph}$, are effective for long-cadence light curves but require rotation periods. In order to improve the utilization of Kepler light curves, we introduce and use the smoothness metric. The smoothness metric is able to analyze stars without a measured rotation period and is applicable for long-cadence light curves. We test and validate our metric, resulting in the detection of the 11 years solar cycle and a 457 days cycle for our prototype star KIC 9017220. We analyze 92,084 Kepler long-cadence light curves, and as our main results, we detect 4455 magnetic activity cycle candidates, but about 20 percent are false cycles and 50 percent are lower limits of the real cycles, and we analyze their causes in detail. As an investigation into the performance of our method, we simulate disturbance factors and prove that the p-value test is invalid under certain circumstances. Full article

Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on the strength of cometary material. This changed with the Rosetta mission and its detailed close observation data and with the landing(s) of Philae in 2014. There are already many articles and reviews in the literature that derive or compile many different strength values from various Rosetta and Philae data. In this paper, we attempt to provide an overview of the available direct and indirect data; we focus on comet Churyumov–Gerasimenko/67P but include a discussion on the Deep Impact strength results. As a prerequisite, we start by giving precise definitions of ‘strength’, discuss soil mechanics based on the Mohr–Coulomb ‘law’ of micro-gravity, and discuss bulk density and porosity, sintering, and the physics of the strength of a cohesive granular medium. We proceed by discussing the scaling of strength with the size and strain rate, which is needed to understand the observational data. We show how measured elastic properties and thermal (conductivity) data can be correlated with strength. Finally, a singular very high strength value is reviewed as well as some particularly small-strength values inferred from the bouncing motion of Philae, data from its collisions with the surface of the comet, and scratch marks it left, allegedly, on the surface close to its final resting site. The synthesis is presented as an overview figure of the tensile and compressive strength of cometary matter as a function of the size scale; conclusions about the size dependence and apparent natural variability of strength are drawn. Full article

We confront $f(T,T_G)$ gravity, with big bang nucleosynthesis (BBN) requirements. The former is obtained using both the torsion scalar, as well as the teleparallel equivalent of the Gauss–Bonnet term, in the Lagrangian, resulting to modified Friedmann equations in which the extra torsional terms constitute an effective dark energy sector. We calculate the deviations of the freeze-out temperature $T_f$, caused by the extra torsion terms in comparison to $\Lambda$CDM paradigm. Then, we impose five specific $f(T,T_G)$ models and extract the constraints on the model parameters in order for the ratio $|\Delta T_f/T_f|$ to satisfy the observational BBN bound. As we find, in most of the models the involved parameters are bounded in a narrow window around their general relativity values as expected, asin the power-law model, where the exponent n needs to be $n\lesssim 0.5$. Nevertheless, the logarithmic model can easily satisfy the BBN constraints for large regions of the model parameters. This feature should be taken into account in future model building. Full article

By using ionosonde data recorded at Chiang Mai (18.8° N, 98.9° E, magnetic latitude is 9.1° N), Puer (22.7° N, 101.1° E, magnetic latitude is 12.9° N), and Leshan (29.6° N, 103.7° E, magnetic latitude is 19.8° N), the statistical features of different types of spread F (SF) occurrence at low and middle latitudes were analyzed in this study. The results showed that the SF occurrence had obvious local time, latitude, and SF-type variations. The range spread F (RSF) occurrence in equinox months decreased with the increase in latitude, while the frequency spread F’s (FSF) occurrence rate in the summer months increased and the onset time of FSF became earlier when the latitude increased. The generation of SF depends on the SF type. A plasma bubble excited by the generalized Rayleigh–Taylor instability (GRT) at the equator is more likely to produce RSF, while nighttime medium-scale traveling ionospheric disturbances (MSTIDs) induced by Perkins instability at middle latitudes is the main reason for the generation of FSF. Full article

In this short review, we discuss how Earth’s climatological and geological history and also how the shadows of galactic black holes might reveal our Universe’s past evolution. Specifically we point out that a pressure singularity that occurred in our Universe’s past might have left its imprint on Earth’s geological and climatological history and on the shadows of cosmological black holes. Our approach is based on the fact that the $H_0$ tension problem may be resolved if some sort of abrupt physics change occurred in our Universe 70–150 Myrs ago, an abrupt change that deeply affected the Cepheid parameters. We review how such an abrupt physics change might have been caused in our Universe by a smooth passage of it through a pressure finite-time singularity. Such finite-time singularities might occur in modified gravity and specifically in $F\left(R\right)$ gravity, so we show how modified gravity might drive this type of evolution, without resorting to peculiar cosmic fluids or scalar fields. The presence of such a pressure singularity can distort the elliptic trajectories of bound objects in the Universe, causing possible geological and climatological changes on Earth, if its elliptic trajectory around the Sun might have changed. Also, such a pressure singularity affects directly the circular photon orbits around supermassive galactic black holes existing at cosmological redshift distances, thus the shadows of some cosmological black holes at redshifts $z\le 0.01$, might look different in shape, compared with the SgrA* and M87* supermassive black holes. This feature however can be checked experimentally in the very far future. Full article

I apply the jittering jets in a cooling flow scenario to explain the two pairs of bubbles in the cooling flow galaxy cluster RBS 797 which are perpendicular to each other and almost coeval, and conclude that the interaction of the jets with the cold dense clumps that feed the supermassive black hole (SMBH) takes place in the zone where the gravitational influence of the SMBH and that of the cluster are about equal. According to the jittering jets in a cooling flow scenario, jets uplift and entrain cold and dense clumps, impart the clumps’ velocity perpendicular to the original jets’ direction, and ‘drop’ them closer to the jets’ axis. The angular momentum of these clumps is at a very high angle compared to the original jets’ axis. When these clumps feed the SMBH in the next outburst (jet-launching episode) the new jets’ axis might be at a high angle to the axis of the first pair of jets. I apply this scenario to recent observations that show the two perpendicular pairs of bubbles in RBS 797 have a small age difference of <10 $\mathrm{Myr}$, and conclude that the jets–clumps interaction takes place at a distance of about ≈10–100 $\mathrm{pc}$ from the SMBH. Interestingly, in this zone, the escape velocity from the SMBH is about equal to the sound speed of the intracluster medium (ICM). I mention two other clusters of galaxies and discuss the implications of this finding. Full article

In this review, we collect, for the first time, old and new research results, and present future perspectives on how hadron production, in high-energy scattering processes, can experimentally probe fundamental questions of quantum gravity. The key observations that ignited the link between the two arenas are the so-called “color-event horizon” of quantum chromodynamics, and the (de)accelerations involved in such scattering processes. Both phenomena point to the Unruh (and related Hawking)-type effects. After the first pioneering investigations, such research studies continued, including studies of the horizon entropy and other “black-hole thermodynamical” behaviors, which incidentally are also part of the frontier of the analog gravity research itself. It has been stressed that the trait d’union between the two phenomenologies is that in both hadron physics and black hole physics, “thermal” behaviors are more easily understood, not as due to real thermalization processes (sometimes just impossible, given the small number of particles involved), but rather to a stochastic/quantum entanglement nature of such temperatures. Finally, other aspects, such as the self-critical organizations of hadronic matter and of black holes, have been recently investigated. The results of those investigations are also summarized and commented upon here. As a general remark, this research line shows that we can probe quantum gravity theoretical constructions with analog systems that are not confined to only the condensed matter arena. Full article

“Non-locality is most naturally incorporated into a theory in which there is a special frame of reference. One possible candidate for this special frame of reference is the one in which the Cosmic Microwave Background (CMB) is isotropic. However, other than the fact that a realistic interpretation of quantum mechanics requires a preferred frame and the CMB provides us with one, there is no readily apparent reason why the two should be linked” (L. Hardy). Starting from this remark, we first argue that, given the present view of the vacuum, the basic tenets of Quantum Field Theory cannot guarantee that Einstein Special Relativity, with no preferred frame, is the physically realized version of relativity. Then, to try to understand the nature of the hypothetical preferred $\Sigma -$frame, we consider the so-called ether drift experiments, those precise optical measurements that try to detect, in the laboratory, a small angular dependence of the two-way velocity of light and then to correlate this angular dependence with the direct CMB observations with satellites in space. By considering all experiments performed so far, from Michelson–Morley to the present experiments with optical resonators, and analyzing the small observed residuals in a modern theoretical framework, the long-sought $\Sigma -$frame tight to the CMB naturally emerges. Finally, if quantum non-locality reflects some effect propagating at vastly superluminal speed $v_{QI}\to \infty$, its ultimate origin could be hidden somewhere in the infinite speed $c_s\to \infty$ of vacuum density fluctuations. Full article

Searches for lepton flavor violation in tau decays are unambiguous signatures of new physics. The branching ratios of tau leptons at the level of ${10}^{-10}$–${10}^{-9}$ can be probed using 50 $a{b}^{-1}$ of electron-positron annihilation data being collected by the Belle II experiment at the world’s highest luminosity accelerator, the SuperKEKB, located at the High Energy Accelerator Research Organization, KEK, in Tsukuba, Japan. Searches with such expected sensitivity will either discover new physics or strongly constrain several new physics models. Full article

Mapping the same volume of space with different tracers allows us to obtain information through estimated quantities exploiting the multi-tracer technique. Indeed, the cross-correlation of different probes provides information that cannot be otherwise obtained. In addition, some estimated quantities are not sensitive to the noise produced by the sampling variance but are only limited by the shot (or Poisson) noise, an attractive perspective. A simple example is the ratio between the (cross)-correlations, measuring the ratio of the bias parameters. Multi-tracer approaches can thereby provide additional information that cannot be extracted from independent volumes. Full article

The existence of gravitational radiation arriving at null infinity ${\mathcal{J}}^{+}$, i.e., escaping from the physical system, is addressed in the presence of a non-negative cosmological constant $\mathsf{\Lambda }\ge 0$. The case with vanishing $\mathsf{\Lambda }$ is well understood and relies on the properties of the News tensor field (or the News function) defined at ${\mathcal{J}}^{+}$. The situation is drastically different when $\mathsf{\Lambda }>0$, where there is no known notion of ‘News’ with similar good properties. In this paper, both situations are considered jointly from a tidal point of view, that is, taking into account the strength (or energy) of the curvature tensors. The fundamental object used for this purposes is the asymptotic (radiant) super-momentum, a causal vector defined at infinity with remarkable properties. This leads to a novel characterization of gravitational radiation valid for the general case with $\mathsf{\Lambda }\ge 0$, which has been proven to be equivalent when $\mathsf{\Lambda }=0$ to the standard one based on News. Here, the implications of this result when $\mathsf{\Lambda }>0$ are analyzed in detail. A general procedure to construct ‘News tensors’ when $\mathsf{\Lambda }>0$ is depicted, a proposal for asymptotic symmetries is provided, and an example of a conserved charge that may detect gravitational radiation at ${\mathcal{J}}^{+}$ is exhibited. A series of illustrative examples is listed as well. Full article

For the efficient identification of quantum states, we propose the notion of linear canonical wavelet transform in the framework of quantum mechanics. Using the machinery of Dirac representation theory and integration within an ordered product of operators, we recast the linear canonical wavelet transform to a matrix element of the squeezing–displacing operator $\mathcal{U}(\mu ,s){\mathcal{K}}_M$ between analyzing vector $⟨\psi |$ and two-mode quantum state vector $|f⟩$ to be transformed. We also derive the inner product relation and inversion formula for the linear canonical wavelet transform in the realm of quantum mechanics. Lastly, we present an explicit example for the lucid implementation of linear canonical wavelet transform in identifying the quantum states. Full article

We derived astroparticle constraints in different dark matter scenarios that are alternatives to cold dark matter (CDM): thermal relic warm dark matter, WDM; fuzzy dark matter, $\psi$DM; self-interacting dark matter, SIDM; sterile neutrino dark matter, $\nu$DM. Our framework is based on updated determinations of the high-redshift UV luminosity functions for primordial galaxies to redshift $z\sim 10$, on redshift-dependent halo mass functions in the above DM scenarios from numerical simulations, and on robust constraints on the reionization history of the Universe from recent astrophysical and cosmological datasets. First, we built an empirical model of cosmic reionization characterized by two parameters, namely the escape fraction $f_{\mathrm{esc}}$ of ionizing photons from primordial galaxies, and the limiting UV magnitude $M_{\mathrm{UV}}^{\lim }$ down to which the extrapolated UV luminosity functions steeply increased. Second, we performed standard abundance matching of the UV luminosity function and the halo mass function, obtaining a relationship between UV luminosity and the halo mass, whose shape depends on an astroparticle quantity X specific to each DM scenario (e.g., WDM particle mass); we exploited such a relationship to introduce (in the analysis) a constraint from primordial galaxy formation, in terms of the threshold halo mass above which primordial galaxies can efficiently form stars. Third, we performed Bayesian inference on the three parameters $f_{\mathrm{esc}}$, $M_{\mathrm{UV}}^{\lim }$, and X via a standard MCMC technique, and compared the outcomes of different DM scenarios on the reionization history. We also investigated the robustness of our findings against educated variations of still uncertain astrophysical quantities. Finally, we highlight the relevance of our astroparticle estimates in predicting the behavior of the high-redshift UV luminosity function at faint, yet unexplored magnitudes, which may be tested with the advent of the James Webb Space Telescope. Full article

A very likely New Physics in plain sight, but that the community does not see, is a second Higgs doublet that has a second set of Yukawa couplings. The extra tt and tc couplings can each drive baryogenesis, with O(1) Higgs quartic couplings providing a first order electroweak phase transition. A natural cancellation mechanism can tame electron EDM, if extra ee, tt couplings “know” the known fermion mass and mixing hierarchies. Colliding c with g produces tH/A, bH${}^{+}$ via extra tc coupling, and together with extra tt coupling give ttc(bar), ttt(bar), and btb(bar) signatures at the LHC. Extra tu coupling can also be probed, but more definitive would be the B to $\mu \nu$ and $\tau \nu$ decay rate ratio. Myriad extra Yukawa couplings can make an impact on flavor physics and CP violation, including on muon g-2. The opening to the prelude of a new physics Higgs and flavor era may unfold before us. Full article

The problem of the boundaries of the Mendeleev table of chemical elements is closely related to the understanding of the properties of nuclear matter. In this regard, the synthesis of superheavy nuclei on accelerators and the registration of their decay products are of fundamental scientific interest. The Joint Institute of Nuclear Research in Dubna (JINR) conducts research on the synthesis of superheavy nuclei on the new DC-280 cyclotron (the Factory of Superheavy Elements). As part of the development of this experiment, the possibility of using phosphate glass as a material for detectors of heavy and superheavy nuclei is being considered. This issue requires test experiments to study the recording properties of the glass at different irradiation and treatment conditions. The article presents a method for identifying heavy ions in phosphate glass detectors under various conditions by the geometric characteristics of ion tracks. The results obtained indicate the possibility of using the KNFS-3 phosphate glass detectors for registration and identification of accelerated superheavy nuclei. Full article

Relativistic plasma can be formed in strong electromagnetic or gravitational fields. Such conditions exist in compact astrophysical objects, such as white dwarfs and neutron stars, as well as in accretion discs around neutron stars and black holes. Relativistic plasma may also be produced in the laboratory during interactions of ultra-intense lasers with solid targets or laser beams between themselves. The process of thermalization in relativistic plasma can be affected by quantum degeneracy, as reaction rates are either suppressed by Pauli blocking or intensified by Bose enhancement. In addition, specific quantum phenomena, such as Bose–Einstein condensation, may occur in such a plasma. In this review, the process of plasma thermalization is discussed and illustrated with several examples. The conditions for quantum condensation of photons are formulated. Similarly, the conditions for thermalization delay due to the quantum degeneracy of fermions are analyzed. Finally, the process of formation of such relativistic plasma originating from an overcritical electric field is discussed. All these results are relevant for relativistic astrophysics as well as for laboratory experiments with ultra-intense lasers. Full article

In solar cycles 23–24, solar activity noticeably decreased and, as a result, solar wind parameters decreased. Based on the measurements of the OMNI base for the period 1976–2019, the time profiles of the main solar wind parameters and magnetospheric indices for the main interplanetary drivers of magnetospheric disturbances (solar wind types CIR. Sheath, ejecta and MC) are studied using the double superposed epoch method. The main task of the research is to compare time profiles for the epoch of high solar activity at 21–22 SC and the epoch of low activity at 23–24 SC. The following results were obtained. (1) The analysis did not show a statistically significant change in driver durations during the epoch of minimum. (2) The time profiles of all parameters for all types of SW in the epoch of low activity have the same shape as in the epoch of high activity, but locate at lower values of the parameters. (3) In CIR events, the longitude angle of the solar wind flow has a characteristic S shape; but in the epoch of low activity, it varies in a larger range than in the previous epoch. Full article

We have studied the variation of the time profile of X-ray emission of solar flares that occurred during the second half of solar cycle 23 (SC 23) and for about the full solar cycle 24 (SC 24) (2002–2018). We define a new index, called the “ratio index” (R_f), for all X-ray solar flares. This index is defined as the ratio of the flare’s rising time interval by its total duration period. According to the ratio index, the X-ray solar flares are classified into two types: (1) sudden flares [R_f < 0.5], and (2) gradual flares [R_f > 0.5]. The sudden flare type, with fast-rising and slow recovery, is more common and represents most of the flares that happen most of the time during the solar cycles but are less common during the minimum solar activity years. On the other hand, the gradual flare type (or R_f > 0.5) is less common but predominates during the minimum solar activity epochs. Sudden flares tend to be strong, large, and numerous in the polar regions, while gradual flares are weak, short, and countable in the latitude range between 50 and 70, both for northern and southern latitudes. However, both types appear to happen in the lower latitudes and the solar equatorial regions. Full article

Nonlocal gravity (NLG) is a classical nonlocal generalization of Einstein’s theory of gravitation developed in close analogy with the nonlocal electrodynamics of media. It appears that the nonlocal aspect of the universal gravitational interaction could simulate dark matter. Within the Newtonian regime of NLG, we investigate the deviation of the gravitational force from the Newtonian inverse square law as a consequence of the existence of the effective dark matter. In particular, we work out the magnitude of this deviation in the solar system out to 100 astronomical units. Moreover, we give an improved lower limit for the short-range parameter of the reciprocal kernel of NLG. Full article

In this paper, the generalized helical hypersurfaces $\mathbf{x}=\mathbf{x}(u,v,w)$ with a time-like axis in Minkowski spacetime ${\mathbb{E}}_1^4$ are considered. The first and the second fundamental form matrices, the Gauss map, and the shape operator matrix of $\mathbf{x}$ are calculated. Moreover, the curvatures of the generalized helical hypersurface $\mathbf{x}$ are obtained by using the Cayley–Hamilton theorem. The umbilical conditions for the curvatures of $\mathbf{x}$ are given. Finally, the Laplace–Beltrami operator of the generalized helical hypersurface with a time-like axis is presented in ${\mathbb{E}}_1^4$. Full article

We propose a new class of cosmological unified dark sector models called “Generalized Logotropic Models”. They depend on a free parameter n. The original logotropic model is a special case of our generalized model corresponding to $n=1$. The $\Lambda$CDM model is recovered for $n=0$. In our scenario, the Universe is filled with a single fluid, a generalized logotropic dark fluid (GLDF), whose pressure P includes higher order logarithmic terms of the rest-mass density ${\rho }_m$. The total energy density $ϵ$ is the sum of the rest-mass energy density ${\rho }_m{c}^2$ and the internal energy density u which play the roles of dark matter energy density ${ϵ}_m$ and dark energy density ${ϵ}_{de}$, respectively. We investigate the cosmological behavior of the generalized logotropic models by focusing on the evolution of the energy density, scale factor, equation of state parameter, deceleration parameter and squared speed of sound. Low values of $n\le 3$ are favored. We also study the asymptotic behavior of the generalized logotropic models. In particular, we show that the model presents a phantom behavior and has three distinct ways of evolution depending on the value of n. For $0<n\le 2$, it leads to a little rip and for $n>2$ to a big rip. We predict the value of the big rip time as a function of n without any free (undetermined) parameter. Full article

Using the Barrow entropy and considering the timescale as IR cutoff, a new holographic dark energy model named Barrow agegraphic dark energy (BADE) was proposed. We use phase space analysis method to discuss the evolution of the universe in three different mode of BADE ($Q=0$; $Q=3\alpha H({\rho }_m+{\rho }_D)$; $Q=H(\alpha {\rho }_m+\beta {\rho }_D)$). We find the attractor which represents the dark energy-dominated era exists in all cases. In the case $Q=0$ and $Q=H(\alpha {\rho }_m+\beta {\rho }_D)$ with $\beta =0$, the attractor can behave as the cosmological constant, and these models can used to mimic the cosmological constant. Full article

In situ recordings by the solar Wind spacecraft reveal the ubiquitousness of alpha particles, whose drift velocities to the background proton $v_{\alpha }$ are generally less than or equal to the local Alfvén velocity $v_A$. The alpha beam instability plays a significant role in the alpha beam deceleration in the solar wind; nonetheless, the detailed mechanism of deceleration remains unclear. By using the linear Vlasov equation of the PDRK/B0 solver, the present work investigates the kinetic instability caused by both the alpha beam and the electron temperature anisotropy in the solar wind and assesses the effects of the electron temperature anisotropy on such instability. The results show that both anisotropic electrons and alpha beams lead to the excitation of several plasma waves, and the wave frequency, growth rate, and polarization properties are sensitive to the electron temperature anisotropy ($T_{e\perp }/T_{e\Vert }$), the parallel electron beta (${\beta }_{e\Vert }$), and the alpha beam drift velocity ($v_{\alpha }/v_A$). With an excess parallel temperature $T_{e\perp }/T_{e\Vert }<1$, the parallel magnetosonic/whistler (PM/W), parallel Alfvén wave (PAW), and oblique Alfvén/ion cyclotron (OA/IC) instabilities could be generated, while for an excess perpendicular temperature $T_{e\perp }/T_{e\Vert }>1$, the PM/W, OA/IC, parallel whistler (PW), and kinetic Alfvén wave (KAW) instabilities could grow. In the region of $T_{e\perp }/T_{e\Vert }<1$, the thresholds of the PM/W, PAW, and OA/IC instabilities extend to lower drift velocity $v_{\alpha }/v_A$. In the region of $T_{e\perp }/T_{e\Vert }>1$, the thresholds of the PM/W and OA/IC instabilities increase, while those of the PW and KAW instabilities are shifted to lower $v_{\alpha }/v_A$. The current study presents a comprehensive overview for alpha beam instabilities that limit the alpha beam drift velocity in the solar wind. Full article

The number ratio of carbon-rich to oxygen-rich asymptotic giant branch (AGB) stars (the so-called C/M ratio) is closely related to the evolution environment of the host galaxy. This work studies the C/M ratio in 14 galaxies within the Local Group with the most complete and clean sample of member stars identified in our previous works. The borderlines between carbon-rich AGB and oxygen-rich AGB stars as well as red supergiants are defined by Gaussian mixture model fitting to the number density in the $(J-K)/K$ diagram for the member stars of the LMC and M33, and then applied to the other galaxies by shifting the difference in the position of tip red giant branch (TRGB). The C/M ratios are obtained after precise and consistent categorization. Although for galaxies with larger distance modulo there is greater uncertainty, the C/M ratio is clearly found to decrease with the color index ${(J-K)}_0$ of TRGB as the indicator of metallicity, which agrees with previous studies and can be explained by the fact that carbon stars are more easily formed in a metal-poor environment. Furthermore, the C/M ratio within M33 is found to increase with galactocentric distance, which coincides with this scenario and the galactic chemical evolution model. On the other hand, the C/M ratio within M31 is found to decrease with galactocentric radius, which deserves further study. Full article

The dark energy from virtual gravitons is consistent with observational data on supernovas with the same accuracy as the ΛCDM model. The fact that virtual gravitons are capable of producing a de Sitter accelerated expansion of the FLRW universe was established in 2008 (see references). The combination of conformal non-invariance with zero rest mass of gravitons (unique properties of the gravitational field) leads to the appearance of graviton dark energy in a mater-dominated era; this fact explains the relatively recent appearance of the dark energy and answers the question “Why now?”. The transition redshifts (where deceleration is replaced by acceleration) that follow from the graviton theory are consistent with model-independent transition redshifts derived from observational data. Prospects for testing the GCDM model (the graviton model of dark energy where G stands for gravitons) and comparison with the ΛCDM model are discussed. Full article

The hybrid and the dressed metric formalisms for the study of primordial perturbations in Loop Quantum Cosmology lead to dynamical equations for the modes of these perturbations that are of a generalized harmonic-oscillator type, with a mass that depends on the background but is the same for all modes. For quantum background states that are peaked on trajectories of the effective description of Loop Quantum Cosmology, the main difference between the two considered formalisms is found in the expression of this mass. The value of the mass at the bounce is especially important, since it is only in a short interval around this event that the quantum geometry effects on the perturbations are relevant. In a previous article, the properties of this mass were discussed for an inflaton potential of quadratic form, or with similar characteristics. In the present work, we extend this study to other interesting potentials in cosmology, namely the Starobinsky and the exponential potentials. We prove that there exists a finite interval of values of the potential (which includes the zero but typically goes beyond the sector of kinetically dominated inflaton energy density) for which the hybrid mass is positive at the bounce whereas the dressed metric mass is negative. Full article

It was shown several years ago that dark matter halo outskirts are characterized by very steep density profiles in a very small radial range. This feature has been interpreted as a pile-up of different particle orbits at a similar location, namely, splashback material at half an orbit after collapse. Adhikari et al. (2014) obtained the location of the splashback radius through a very simple model by calculating a dark matter shell trajectory in the secondary infall model while it crosses a growing NFW profile-shaped dark matter halo. Because they imposed a halo profile instead of calculating it from the trajectories of the shells of dark matter, they were not able to find the dark matter profile around the splashback radius. In the present paper, we use an improved spherical infall model taking into account shell crossing as well as several physical effects such as ordered and random angular momentum, dynamical friction, adiabatic contraction, etc. This allows us to determine the density profile from the inner to the outer region and to study the behavior of the outer density profile. We compare the density profiles and their logarithmic slope of with the simulation results of Diemer and Kravtsov (2014), finding a good agreement between the prediction of the model and the simulations. Full article