There is No Missing Satellites Problem [CEA]

A critical challenge to the cold dark matter (CDM) paradigm is that there are fewer satellites observed around the Milky Way than found in simulations of dark matter substructure. We show that there is a match between the observed satellite counts corrected by the detection efficiency of the Sloan Digital Sky Survey (for luminosities $L \gtrsim$ 340 L$\odot$) and the number of luminous satellites predicted by CDM, assuming an empirical relation between stellar mass and halo mass. The “issing satellites problem”, cast in terms of number counts, is thus solved, and imply that luminous satellites inhabit subhalos as small as 10$^7-$10$^8$ M$\odot$. The total number of Milky Way satellites depends sensitively on the spatial distribution of satellites. We also show that warm dark matter (WDM) models with a thermal relic mass smaller than 4 keV are robustly ruled out, and that limits of $m_\text{WDM} \gtrsim 8$ keV from the Milky Way are probable in the near future. Similarly stringent constraints can be placed on any dark matter model that leads to a suppression of the matter power spectrum on $\sim$10$^7$ M$\odot$ scales. Measurements of completely dark halos below $10^8$ M$\odot$, achievable with substructure lensing, are the next frontier for tests of CDM.

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S. Kim, A. Peter and J. Hargis
Mon, 20 Nov 17

Comments: 9 pages, 6 figures, and 3 tables (includes supplementary material). Key results are summarized in Figure 2. To be submitted to PRL. Comments welcome!

Modelling Baryonic Effects on Galaxy Cluster Mass Profiles [CEA]

Gravitational lensing is a powerful probe of the mass distribution of galaxy clusters and cosmology. However, accurate measurements of the cluster mass profiles is limited by the still poorly understood cluster astrophysics. In this work, we present a physically motivated model of baryonic effects on the cluster mass profiles, which self-consistently takes into account the impact of baryons on the concentration as well as mass accretion histories of galaxy clusters. We calibrate this model using the Omega500 hydrodynamical cosmological simulations of galaxy clusters with varying baryonic physics. Our model will enable us to simultaneously constrain cluster mass, concentration, and cosmological parameters using stacked weak lensing measurements from upcoming optical cluster surveys.

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M. Shirasaki, E. Lau and D. Nagai
Mon, 20 Nov 17

Comments: 12 pages, 7 figures, 2 tables, submitted to MNRAS

Correlations in the three-dimensional Lyman-alpha forest contaminated by high column density absorbers [CEA]

Correlations measured in 3D in the Lyman-alpha forest are contaminated by the presence of the damping wings of high column density (HCD) absorbing systems of neutral hydrogen (HI; having column densities $N(\mathrm{HI}) > 1.6 \times 10^{17}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$), which extend significantly beyond the redshift-space location of the absorber. We measure this effect as a function of the column density of the HCD absorbers and redshift by measuring 3D flux power spectra in cosmological hydrodynamical simulations from the Illustris project. Survey pipelines exclude regions containing the largest damping wings. We find that, even after this procedure, there is a scale-dependent correction to the 3D Lyman-alpha forest flux power spectrum from residual contamination. We model this residual using a simple physical model of the HCD absorbers as linearly biased tracers of the matter density distribution, convolved with their Voigt profiles and integrated over the column density distribution function. We recommend the use of this model over existing models used in data analysis, which approximate the damping wings as top-hats and so miss shape information in the extended wings. The simple linear Voigt model is statistically consistent with our simulation results for a mock residual contamination up to small scales ($k < 1\,h\,\mathrm{Mpc}^{-1}$), even though it cannot account for the effect of the highest column density absorbers (which are in any case preferentially removed from survey data) on the smallest scales (e.g., $k > 0.4\,h\,\mathrm{Mpc}^{-1}$ for small DLAs; $N(\mathrm{HI}) \sim 10^{21}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$). Our model is appropriate for an accurate analysis of the baryon acoustic oscillations feature and it is additionally essential for reconstructing the full shape of the 3D flux power spectrum, assuming that the highest column density absorbers are removed.

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K. Rogers, S. Bird, H. Peiris, et. al.
Mon, 20 Nov 17

Comments: 12 pages, 9 figures. To be submitted to MNRAS

Confronting the Potential-driven DBI-inspired nonminimal kinetic coupling (Dinkic) inflation to the observational data [CEA]

In the previous work, a new kind of inflation model was proposed, which has the interesting property that its perturbation equation of motion gets a correction of k^4, due to the non-linearity of the kinetic term. Nonetheless, the scale-invariance of the power spectrum remains valid, both in large-k and small-k limits. In this paper, we investigate in detail the spectral index, the index running and the tensor/scalar ratio in this model, especially on the potential-driven case, and compare the results to the current PLANCK/BICEP observational data. We also discuss the tensor spectrum in this case, which is expected to be tested by the future observations on primordial gravitational waves.

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J. Chen, H. Wenjie, D. Hou, et. al.
Mon, 20 Nov 17

Comments: N/A

Clustering of Galaxies with f(R) gravity [CEA]

Based on thermodynamics, we discuss the galactic clustering of expanding Universe by assuming the gravitational interaction through the modified Newton’s potential given by $f(R)$ gravity. We compute the corrected $N$-particle partition function analytically. The corrected partition function leads to more exact equations of states of the system. By assuming that system follows quasi-equilibrium, we derive the exact distribution function which exhibits the $f(R)$ correction. Moreover, we evaluate the critical temperature and discuss the stability of the system. We observe the effects of correction of $f(R)$ gravity on the power law behavior of particle-particle correlation function also. In order to check feasibility of an $f(R)$ gravity approach to the clustering of galaxies, we compare our results with an observational galaxy cluster catalog.

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S. Capozziello, M. Faizal, M. Hameeda, et. al.
Mon, 20 Nov 17

Comments: 14 pages, 8 figures, 1 table; accepted for publication on MNRAS

Vainshtein mechanism after GW170817 [CEA]

The almost simultaneous detection of gravitational waves and a short gamma-ray burst from a neutron star merger has put a tight constraint on the difference between the speed of gravity and light. In the four-dimensional scalar-tensor theory with second order equations of motion, the Horndeski theory, this translates into a significant reduction of the viable parameter space of the theory. Recently, extensions of Horndeski theory, which are free from Ostrogradsky ghosts despite the presence of higher order derivatives in the equations of motion, have been identified and classified exploiting the degeneracy criterium. In these new theories, the fifth force mediated by the scalar field must be suppressed in order to evade the stringent Solar System constraints. We study the Vainshtein mechanism in the most general degenerate higher order scalar-tensor theory in which light and gravity propagate at the same speed. We find that the Vainshtein mechanism generally works outside a matter source but it is broken inside matter, similarly to beyond Horndeski theories. This leaves interesting possibilities to test these theories that are compatible with gravitational wave observations using astrophysical objects.

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M. Crisostomi and K. Koyama
Mon, 20 Nov 17

Comments: 5 pages, no figure

Primordial black hole detection through diffractive microlensing [CEA]

Recent observations of the gravitational wave by LIGO motivates investigations for the existence of Primordial Black Holes (PBHs) as a candidate for the dark matter. We propose quasar gravitational microlensing observations in Infrared to the sub-millimeter wavelengths by sub-lunar PBHs as lenses. The advantage of observations in the longer wavelengths is that the Schwarzschild radius of the lens is of the order of the wavelength (i.e. $R_{\rm sch}\simeq \lambda$), so the wave optics features of gravitational lensing can be seen on the cosmological scales. In the wave optics regime, the magnification has a periodic profile rather than monotonic one in the geometric case. This observation can break the degeneracy between the lens parameters and determine uniquely the lens mass as well as its distance from the observer. We estimate the wave optics optical-depth and number of detectable events for sub-lunar lenses and propose a long-term survey of quasars with cadence $\sim$ hour to probe possible fraction of dark matter in form of sub-lunar PBHs.

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T. Naderi, A. Mehrabi and S. Rahvar
Mon, 20 Nov 17

Comments: 6 pages, 4 figures, comments welcome