48,605 research outputs found
Quantum WDM fermions and gravitation determine the observed galaxy structures
Quantum mechanics is necessary to compute galaxy structures at kpc scales and
below. This is so because near the galaxy center, at scales below 10 - 100 pc,
warm dark matter (WDM) quantum effects are important: observations show that
the interparticle distance is of the order of, or smaller than the de Broglie
wavelength for WDM. This explains why all classical (non-quantum) WDM N-body
simulations fail to explain galactic cores and their sizes. We describe
fermionic WDM galaxies in an analytic semiclassical framework based on the
Thomas-Fermi approach, we resolve it numerically and find the main physical
galaxy magnitudes: mass, halo radius, phase-space density, velocity dispersion,
fully consistent with observations, including compact dwarf galaxies. Namely,
fermionic WDM treated quantum mechanically, as it must be, reproduces the
observed galaxy DM cores and their sizes. [In addition, as is known, WDM
simulations produce the right DM structures in agreement with observations for
scales > kpc]. We show that compact dwarf galaxies are natural quantum
macroscopic objects supported against gravity by the fermionic WDM quantum
pressure (quantum degenerate fermions) with a minimal galaxy mass and minimal
velocity dispersion. Interestingly enough, the minimal galaxy mass implies a
minimal mass m_{min} for the WDM particle. The lightest known dwarf galaxy
(Willman I) implies m > m_{min} = 1.91 keV. These results and the observed halo
radius and mass of the compact galaxies provide further indication that the WDM
particle mass m is approximately around 2 keV.Comment: 15 pages, 2 figures, expanded version to appear in Astroparticle
Physics. admin note: substantial text overlap with arXiv:1204.309
Warm dark matter primordial spectra and the onset of structure formation at redshift z
Analytic formulas reproducing the warm dark matter (WDM) primordial spectra
are obtained for WDM particles decoupling in and out of thermal equilibrium
which provide the initial data for WDM non-linear structure formation. We
compute and analyze the corresponding WDM overdensities and compare them to the
CDM case. We consider the ratio of the WDM to CDM primordial spectrum and the
WDM to CDM overdensities: they turn to be self-similar functions of k/k_{1/2}
and R/R_{1/2} respectively, k_{1/2} and R_{1/2} being the wavenumber and length
where the WDM spectrum and overdensity are 1/2 of the respective CDM
magnitudes. Both k_{1/2} and R_{1/2} show scaling as powers of the WDM particle
mass m while the self-similar functions are independent of m. The WDM
primordial spectrum sharply decreases around k_{1/2} with respect to the CDM
spectrum, while the WDM overdensity slowly decreases around R_{1/2}. The
nonlinear regions where WDM structure formation takes place are shown and
compared to those in CDM: the WDM non-linear structures start to form later
than in CDM, and as a general trend, decreasing the DM particle mass delays the
onset of the non-linear regime. The non-linear regime starts earlier for
smaller objects than for larger ones; smaller objects can form earlier both in
WDM and CDM. We compute and analyze the differential mass function dN/dM for
WDM at redshift z in the Press-Schechter approach. The WDM suppression effect
of small scale structure increases with the redshift z. Our results for dN/dM
are useful to be contrasted with observations, in particular for 4 < z < 12. We
perfom all these studies for the most popular WDM particle physics models.
Contrasting them to observations should point out the precise value of the WDM
particle mass in the keV scale, and help to single out the best WDM particle
physics model (Abridged).Comment: 18 pages, 8 figures. To appear in Phys Rev
The pre-inflationary and inflationary fast-roll eras and their signatures in the low CMB multipoles
We study the entire coupled evolution of the inflaton and the scale factor
for general initial conditions at a given initial time. The generic early
universe evolution has three stages: decelerated fast-roll followed by
inflationary fast roll and then inflationary slow-roll. This evolution is valid
for all regular inflaton potentials. In addition, we find a special (extreme)
slow-roll solution starting at t = -infty in which the fast-roll stages are
absent. At some time t = t_*, the generic evolution backwards in time reaches a
mathematical singu- larity where a(t) vanishes and Hubble becomes singular. We
find the general behaviour near the singularity. The classical inflaton
description is valid for t-t_* > 10 t_{Planck} well before the beginning of
inflation, quantum loop effects are negligible there. The singularity is never
reached in the validity region of the classical treatment and therefore it is
not a real physical phenomenon here. The whole evolution of the fluctuations is
computed. The Bunch-Davies initial conditions (BDic) are generalized for the
present case. The power spectrum gets dynamically modified by the effect of the
fast-roll eras and the BDic choice at a finite time through the transfer
function D(k) of initial conditions. D(0) = 0. D(k) presents a first peak for k
~ 2/eta_0 (eta_0 being the conformal initial time), then oscillates with
decreasing amplitude and vanishes asymptotically for k -> infty. The transfer
function D(k) affects the low CMB multipoles C_l: the change Delta C_l/C_l for
l=1-5 is computed as a function of the starting instant of the fluctuations
t_0. CMB quadrupole observations give large suppressions which are well
reproduced here(Abridged)Comment: 31 pages, 10 figures. Version to appear in PR
Highlights and Conclusions of the Chalonge 14th Paris Cosmology Colloquium 2010: `The Standard Model of the Universe: Theory and Observations'
The Chalonge 14th Paris Cosmology Colloquium was held on 22-24 July 2010 in
Paris Observatory on the Standard Model of the Universe: News from WMAP7,
BICEP, QUAD, SPT, AMI, ACT, Planck, QUIJOTE and Herschel; dark matter (DM)
searches and galactic observations; related theory and simulations. %aiming
synthesis, progress and clarification. P Biermann, D Boyanovsky, A Cooray, C
Destri, H de Vega, G Gilmore, S Gottlober, E Komatsu, S McGaugh, A Lasenby, R
Rebolo, P Salucci, N Sanchez and A Tikhonov present here their highlights of
the Colloquium. Inflection points emerged: LambdaWDM (Warm DM) emerges
impressively over LambdaCDM whose galactic scale problems are ever-increasing.
Summary and conclusions by H. J. de Vega, M. C. Falvella and N. G. Sanchez
stress among other points: (i) Primordial CMB gaussianity is confirmed.
Inflation effective theory predicts a tensor to scalar ratio 0.05-0.04 at
reach/border line of next CMB observations, early fast-roll inflation provides
lowest multipoles depression. SZ amplitudes are smaller than expected: CMB and
X-ray data agree but intracluster models need revision and relaxed/non-relaxed
clusters distinction. (ii) cosmic ray positron excess is explained naturally by
astrophysical processes, annihilating/decaying dark matter needs growing
tailoring. (iii) Cored (non cusped) DM halos and warm (keV scale mass) DM are
increasingly favored from theory and observations, naturally producing observed
small scale structures, wimps turn strongly disfavoured. LambdaWDM 1 keV
simulations well reproduce observations. Evidence that LambdaCDM does not work
at small scales is staggering. P Biermann presents his live minutes of the
Colloquium and concludes that a keV sterile neutrino is the most interesting DM
candidate. Photos of the Colloquium are included.Comment: 58 pages, 20 figures. Three contributions added: G. Gilmore, S.
Gottlober and E. Komats
Effects of drop and film viscosity on drop impacts onto thin films
While drop-film impacts have been studied extensively in the past, little thought has been given towards separating the effects of the drop fluid properties from those of the film. Distinguishing between the behaviors resulting from characteristics of each independently could provide insight into the underlying physical phenomena with a clarity that is unavailable when the drop and the film consist of identical liquids. In this study, the viscosity is the central parameter varied in both drop and film liquid. Using water, aqueous glycerol mixtures, and Fluoroinert FC-72, a range of kinematic viscosity covering 3 orders of magnitude (4 × 10-7 - 6.5 × 10 -4 m2/s) is examined; a smaller range of surface tension (0.024-0.072 N/m) is covered, as well. Drop impacts occur over a range of Weber numbers from 20 to 3000 and Reynolds numbers from 20 to 14000. Impact outcomes categorized are both formation of a crown and splashing from the crown. Criteria for each impact outcome are presented in light of both film and drop properties; certain outcomes are found to depend more strongly on either the properties of the drop or the film individually. Crown formation appears to relate more strongly to the film's properties, whereas crown splashing has some dependence on the drop properties. Existing splashing correlations are examined in light of the separation of properties. © 2013 by Begell House, Inc
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