Abstract In the past few decades, many studies revealed that there exist some apparent universal relations that can describe the dynamical properties in galaxies. In particular, the radial ...acceleration relation (RAR) is one of the most popular relations discovered recently that can be regarded as a universal law to connect the dynamical radial acceleration with the baryonic acceleration in galaxies. This has revealed an unexpected close connection between dark matter and baryonic matter in galaxies. In this article, by following the recent robust Galactic rotation curve analyzes, we derive the Galactic RAR (GRAR) and show for the first time that the alleged best-fit universal RAR deviates from the GRAR data at more than 5 σ . This provides a strong evidence to falsify the universal nature of RAR in galaxies claimed in past studies.
What If Planet Nine Has Satellites? Chan, Man Ho
Astrophysical journal/The Astrophysical journal,
02/2023, Letnik:
944, Številka:
2
Journal Article
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Odprti dostop
Abstract
In the past decade, numerical simulations started to reveal the possible existence of Planet Nine in our solar system. The Planet Nine scenario can provide an excellent explanation for the ...clustering in orbital elements for Kuiper Belt objects. However, no optical counterpart has been observed so far to verify the Planet Nine scenario. Therefore, some recent studies suggest that Planet Nine could be a dark object, such as a primordial black hole. In this article, we show that the probability of capturing large trans-Neptunian objects by Planet Nine to form a satellite system in the scattered disk region (between the inner Oort Clouds and the Kuiper Belt) is large. By adopting a benchmark model of Planet Nine, we show that the tidal effect can heat up the satellites significantly, which can give sufficient thermal radio flux for observations, even if Planet Nine is a dark object. This provides a new, indirect way for examining the Planet Nine hypothesis and revealing the basic properties of Planet Nine.
Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near Formula: ...see text μeV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency Formula: see text GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion-photon coupling constant can be constrained to Formula: see text GeVFormula: see text for Formula: see text μeV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).
Recent observations of the Cosmic Microwave Background and the Hubble Space Telescope obtain two different values of the Hubble constant with a discrepancy of at least
4.4
σ
, which is now known as ...the Hubble tension. On the other hand, observations of 21-cm signal from the EDGES experiment reveal an unexpected excess absorption trough. These results give a big challenge to the standard cosmological model – the
Λ
CDM model. In this article, we propose that the existence of a cosmological ultra-low frequency radio background (ULFRB) can simultaneously reconcile both discrepancies. The best-fit amounts of the energy density of this additional radio component based on the two problems give an excellent agreement with each other. The extra radio component could be arisen from the simulated decay of axions in the early universe.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Galaxy clusters are good targets for examining our understanding of cosmology. Apart from numerical simulations and gravitational lensing, X-ray observation is the most common and ...conventional way to analyze the gravitational structures of galaxy clusters. Therefore, it is valuable to have simple analytical relations that can connect the observed distribution of the hot, X-ray-emitting gas to the structure of the dark matter in the clusters as derived from simulations. In this article, we apply a simple framework that can analytically connect the hot gas empirical parameters with the standard parameters in the cosmological cold dark matter model. We have theoretically derived two important analytic relations,
r
s
≈
3
r
c
and
ρ
s
≈
9
β
kT
/
8
π
Gm
g
r
c
2
, which can easily relate the dark matter properties in galaxy clusters with the hot gas properties. This can give a consistent picture describing gravitational astrophysics for galaxy clusters by the hot gas and cold dark matter models.
Coronavirus disease 2019 (COVID-19) has led to radical changes in social distancing awareness and affected social relationships. Owing to large-scale lockdown, home quarantine and social distancing ...requirements, it was anticipated that sexual activities would be severely impacted. However, retrospective self-report studies showed that pornography use and autoerotism increased during the pandemic.
This study used big-data databases available on the Internet to investigate factors that modulated pornography use during the pandemic.
Daily relative search volume (RSV) data from Google Trends for the period from 24 February 2020 to 13 July 2020 were extracted. Pornhub traffic data were extracted from the Pornhub Insights website, for the period from 24 February 2020 to 13 July 2020. The parameter was defined as 'percent change in traffic compared to an average day in 2019'. The number of daily new cases of COVID-19 was extracted from the database on Our World in Data.
The normality of the data was examined using the Shapiro-Wilk test. All variables included in this study were non-normally distributed. Therefore, non-parametric tests or parametric tests with bootstrapping were adopted where appropriate.
According to Google Trends, the RSV for 'pornography' increased after late March 2020, which is close to the date when the World Health Organization declared COVID-19 a global pandemic. The number of daily new cases of COVID-19 was positively correlated with the traffic of Pornhub, a popular pornography website, and the RSV for 'pornography'. Moderation analysis demonstrated a significant main effect of daily new cases of COVID-19 and the RSV for 'social distancing' in predicting Pornhub traffic/RSV for 'pornography'. Furthermore, the RSV for 'social distancing' significantly moderated the relationship between daily new cases and Pornhub traffic/RSV for 'pornography'. A stronger COVID-pornography use association was observed with increased social distancing awareness.
Increased pornography consumption during the pandemic was observed, and it was associated with the severity of the pandemic. Social distancing awareness could be a key factor influencing interest in and use of pornography. Further studies on the changes in sexual desire and birth-rate control are worthwhile because long-term public health may be affected by the changes in sexual behaviour during the pandemic.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Recent studies of gamma-ray, cosmic-ray, and radio data put stringent constraints on the fraction of primordial black holes (PBHs) in our universe. In this article, we propose a new indirect ...method in using the X-ray luminosity data of cool-core clusters to constrain the evaporating PBH fraction for the monochromatic, log-normal and power-law mass distributions. The present results show that the amount of evaporating PBHs only constitutes a minor component of dark matter for a large parameter space. The constraints are consistent with and close to that obtained from other cosmic-ray and multiwavelength observations.
Recently, a study has shown that the Bose-Einstein condensates (BECs) formed by the d*(2380) hexaquarks (d*(2380)-BECs) can be thermally produced in the early universe and they are stable enough to ...be a competitive candidate for dark matter. Searching for the decaying signature of d*(2380)-BECs is a possible way to verify this dark matter model. In this article, we discuss the scattering and decaying properties of the d*(2380)-BECs and we show that the decay rate of the d*(2380)-BECs is correlated with the TeV cosmic-ray flux. The predicted average decay rate in our Galaxy is several orders of magnitude larger than the current observed upper limit. Therefore, it would be very difficult for us to search for the decaying signature of the d*(2380)-BEC dark matter model. Nevertheless, the size of the d*(2380)-BECs may be large enough to have self-interaction so that we can possibly detect them in the future.
Abstract
Recent radio observations have obtained stringent constraints for annihilating dark matter. In this article, we use the radio continuum spectral data of the Large Magellanic Cloud to analyze ...the dark matter annihilation signals. We have discovered a slightly positive signal of dark matter annihilation with a 1.5
σ
statistical significance. The overall best-fit dark matter mass is
m
DM
≈ 90 GeV, annihilating via the
b
b
¯
channel. We have also constrained the 3
σ
lower limits of dark matter mass with the standard thermal dark matter annihilation cross section for the
e
+
e
−
,
μ
+
μ
−
,
τ
+
τ
−
, and
b
b
¯
channels.
In the past decade, gamma-ray observations and radio observations of our Milky Way and the Milky Way dwarf spheroidal satellite galaxies put very strong constraints on annihilation cross sections of ...dark matter. In this paper, we suggest a new target object (NGC 2976) that can be used for constraining annihilating dark matter. The radio and X-ray data of NGC 2976 can put very tight constraints on the leptophilic channels of dark matter annihilation. The lower limits of dark matter mass annihilating via , , and channels are 200 GeV, 130 GeV, and 110 GeV, respectively, with the canonical thermal relic cross section. We suggest that this kind of large nearby dwarf galaxy with a relatively high magnetic field can be a good candidate for constraining annihilating dark matter in future analyses.
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