We study, for the first time, how shear and angular momentum modify typical parameters of the spherical collapse model, in dark-energy-dominated universes. In particular, we study the linear density ...threshold for collapse δc and the virial overdensity ΔV for several dark energy models and its influence on the cumulative mass function. The equations of the spherical collapse are those obtained in Pace et al., who used the fully non-linear differential equation for the evolution of the density contrast derived from Newtonian hydrodynamics, and assumed that dark energy is present only at the background level. With the introduction of the shear and rotation terms, the parameters of the spherical collapse model are now mass dependant. The results of the paper show, as expected, that the new terms considered in the spherical collapse model oppose the collapse of perturbations on galactic scale giving rise to higher values of the linear overdensity parameter with respect to the non-rotating case. We find a similar effect also for the virial overdensity parameter. For what concerns the mass function, we find that its high-mass tail is suppressed, while the low-mass tail is slightly affected except in some cases, e.g. the Chaplygin gas case.
We continue the study of the impact of baryon physics on the small scale problems of the ΛCDM model, based on a semi-analytical model (Del Popolo, 2009). With such model, we show how the cusp/core, ...missing satellite (MSP), Too Big to Fail (TBTF) problems and the angular momentum catastrophe can be reconciled with observations, adding parent-satellite interaction. Such interaction between dark matter (DM) and baryons through dynamical friction (DF) can sufficiently flatten the inner cusp of the density profiles to solve the cusp/core problem. Combining, in our model, a Zolotov et al. (2012)-like correction, similarly to Brooks et al. (2013), and effects of UV heating and tidal stripping, the number of massive, luminous satellites, as seen in the Via Lactea 2 (VL2) subhaloes, is in agreement with the numbers observed in the MW, thus resolving the MSP and TBTF problems. The model also produces a distribution of the angular spin parameter and angular momentum in agreement with observations of the dwarfs studied by van den Bosch, Burkert, and Swaters (2001)
This paper provides a review of the types of dark matter that are thought to be fundamental components of the Universe, and their role in the origin and evolution of structures, together with some ...new original results concerning improvements to the spherical collapse model. In particular, we show how the spherical collapse model is modified when dynamical friction and tidal torques are taken into account.
We study, by means of the model proposed in Del Popolo (2009), the effect of baryon physics on the small scale problems of the CDM model. We show that, using this model, the cusp/core problem, the ...missing satellite problem (MSP), the Too Big to Fail (TBTF) problem, and the angular momentum catastrophe can be reconciled with observations. Concerning the cusp/core problem, the interaction among dark matter (DM) and baryonic clumps of 1% the mass of the halo, through dynamical friction (DF), is able to flatten the inner cusp of the density profiles. We moreover assume that haloes form primarily through quiescent accretion, in agreement with the spherical collapse model (SCM)-secondary infall model (SIM) prescriptions. The results of this paper follow from the two assumptions above. Concerning the MSP and TBTF problem, applying to the Via Lactea II (VL2) subhaloes a series of corrections similar to those of Brooks et al. (2013), namely applying a Zolotov et al. (2012)-like correction obtained with our model, and further correcting for the UV heating and tidal stripping, we obtain that the number of massive, luminous satellites is in agreement with the number observed in the MW. The model also produces an angular momentum distribution in agreement with observations, that is with the distribution of the angular spin parameter and angular momentum of the dwarfs studied by van den Bosch, Burkert, and Swaters (2001). In conclusion, the small scale problems of the CDM model can all be solved by introducing baryon physics.
Barions and ΛCDM Model Problems Del Popolo, A.; Le Delliou, M.
Astronomy reports,
02/2022, Letnik:
66, Številka:
2
Journal Article
Recenzirano
We examine the inner profiles of the rotation curves of galaxies in the velocity range from dwarf galaxies to Milky-way like galaxies, having maximum of rotation,
, in the range (30–250) km/s, whose ...diversity is much larger than that predicted by the
CDM model. After showing that the scatter in the observed rotation curves is much larger that predicted by dark matter-only cosmologies, we show how taking into account baryons, through a semi-analytical code, allows to create a a variety of rotation curves in agreement with observation. Simultaneously, we show that the quoted discrepancy does not need for different form of dark matter as advocated by other authors. We finally show how our model can reobtain the rotation curve of remarkable outliers like IC 2574, a 8 kpc cored profile having a challenging, and extremely low rising rotation curve, and UGC 5721 a cusp-like rotation curve galaxy. We suggest treating baryonic physics properly before introducing new exotic features, albeit legitimate, in the standard cosmological model.
Linelike features in TeV γ rays constitute a "smoking gun" for TeV-scale particle dark matter and new physics. Probing the Galactic Center region with ground-based Cherenkov telescopes enables the ...search for TeV spectral features in immediate association with a dense dark matter reservoir at a sensitivity out of reach for satellite γ-ray detectors, and direct detection and collider experiments. We report on 223 hours of observations of the Galactic Center region with the MAGIC stereoscopic telescope system reaching γ-ray energies up to 100 TeV. We improved the sensitivity to spectral lines at high energies using large-zenith-angle observations and a novel background modeling method within a maximum-likelihood analysis in the energy domain. No linelike spectral feature is found in our analysis. Therefore, we constrain the cross section for dark matter annihilation into two photons to ⟨σv⟩≲5×10^{-28} cm^{3} s^{-1} at 1 TeV and ⟨σv⟩≲1×10^{-25} cm^{3} s^{-1} at 100 TeV, achieving the best limits to date for a dark matter mass above 20 TeV and a cuspy dark matter profile at the Galactic Center. Finally, we use the derived limits for both cuspy and cored dark matter profiles to constrain supersymmetric wino models.
According to the now strongly supported concordance Λ cold dark matter model, galaxies may be grossly described as a luminous component embedded in a dark matter halo. The density profile of these ...mass-dominating haloes may be determined by N-body simulations which mimic the evolution of the tiny initial density perturbations during the process leading to the structures we observe today. Unfortunately, when the effect of baryons is taken into account, the situation gets much more complicated due to the difficulties in simulating their physics. As a consequence, a definitive prediction of how dark matter haloes should presently look is still missing. We revisit here this issue from an observational point of view devoting our attention to dwarf galaxies. Being likely dark matter dominated, these systems are ideal candidates to investigate the present-day halo density profiles and check whether dark matter related quantities correlate with stellar ones or the environment. By fitting a large sample of well-measured rotation curves, we infer constraints on both halo structural parameters (such as the logarithmic slope of the density profile and its concentration) and derived quantities (e.g. the mass fraction and the Newtonian acceleration) which could then be used to constrain galaxy formation scenarios. Moreover, we investigate whether the halo properties correlate with the environment the galaxy lives in, thus offering a new tool to deepen our understanding of galaxy formation.
Shear and rotation in Chaplygin cosmology Del Popolo, A.; Pace, F.; Maydanyuk, S. P. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
02/2013, Letnik:
87, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We study the effect of shear and rotation on results previously obtained dealing with the application of the spherical collapse model (SCM) to generalized Chaplygin gas (gCg)-dominated universes. The ...system is composed of baryons and gCg and the collapse is studied for different values of the parameter alpha of the gCg. We show that the joint effect of shear and rotation is that of slowing down the collapse with respect to the simple SCM. This result is of utmost importance for the so-called unified dark matter models, since the described slowdown in the growth of density perturbations can solve one of the main problems of the quoted models, namely the instability described in previous papers e.g., H. B. Sandvik et al., Phys. Rev. D 69, 123524 (2004) at the linear perturbation level.
In this paper, we extend the Romanowsky and Fall (2012) results concerning the stellar angular momentum to the mass range 10
3
≲
M
*
/
M
⊙
≲ 10
12
, and using this result, we calculate the inner ...slope,
α
of haloes density profiles in terms of
V
rot
, by using a previous model of Del Popolo, taking into account the interactions between dark matter and baryons through dynamical friction. Using the McConnachie sample, and that of Romanowsky and Fall, based only on observations, we show that in the quoted sample the rotationally supported galaxies, and the pressure supported ones are divided by a break at
M
*
≃ 10
7.8
M
⊙
. Then we show that the slope
α
flattens monotonically, from
α
≃ − 1 to
α
≃ 0. The flattening is due to the increase of specific angular momentum moving fromMilkyWay-type galaxies to disk dwarf galaxies. Since at
M
*
< 10
7.8
M
⊙
, non-rotational supported galaxies start to dominate, the inner slope steepens again. The paper also extends the main result of Del Popolo (2016) to morphologies different from spheroids, and disks, taking into account the different morphologies delimited by the quoted ones. We finally compared our results with Di Cintio SPH simulations. The two models differ mainly at stellar masses smaller than
M
*
≲ 10
7.8
M
⊙
. In our model the inner slope is flatter than in simulations. This imply that even finding a cored,
α
≃ 0.4, profile in dSphs with masses slightly smaller than ≃10
6
M
⊙
will not imply necessarily a problem for the ΛCDM mode, as predicted by some simulations. To check which one of the two model was better describing data in this region, we used the LITTLE THINGS data, and compared the two models through a
χ
2
, finding that our model gives a better description of the data.
Instantons, which are nonperturbative solutions to Yang-Mills equations, provide a signal for the occurrence of quantum tunneling between distinct classes of vacua. They can give rise to decays of ...particles otherwise forbidden. Using data collected at the Pierre Auger Observatory, we search for signatures of such instanton-induced processes that would be suggestive of super-heavy particles decaying in the Galactic halo. These particles could have been produced during the post-inflationary epoch and match the relic abundance of dark matter inferred today. The nonobservation of the signatures searched for allows us to derive a bound on the reduced coupling constant of gauge interactions in the dark sector: α_{X}≲0.09, for 10^{9}≲M_{X}/GeV<10^{19}. Conversely, we obtain that, for instance, a reduced coupling constant α_{X}=0.09 excludes masses M_{X}≳3×10^{13} GeV. In the context of dark matter production from gravitational interactions alone, we illustrate how these bounds are complementary to those obtained on the Hubble rate at the end of inflation from the nonobservation of tensor modes in the cosmological microwave background.
PDF
