arXiv subjects

J. A. Schewtschenko

Publications and source records attributed to J. A. Schewtschenko.

4 recordsLinked to original sources

arXiv2016

Dark matter-radiation interactions: the structure of Milky Way satellite galaxies

In the thermal dark matter (DM) paradigm, primordial interactions between DM and Standard Model particles are responsible for the observed DM relic density. In Boehm et al. (2014), we showed that weak-strength interactions between DM and radiation (photons or neutrinos) can erase small-scale density fluctuations, leading to a suppression of the matter power spectrum compared to the collisionless cold DM (CDM) model. This results in fewer DM subhaloes within Milky Way-like DM haloes, implying a reduction in the abundance of satellite galaxies. Here we use very high resolution N-body simulations to measure the dynamics of these subhaloes. We find that when interactions are included, the largest subhaloes are less concentrated than their counterparts in the collisionless CDM model and have rotation curves that match observational data, providing a new solution to the "too big to fail" problem.

astro-ph.CO↗

arXiv2015

Dark matter-radiation interactions: the impact on dark matter haloes

Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe suppress density fluctuations on small mass scales. Here we perform a thorough analysis of structure formation in the fully non-linear regime using N-body simulations for models with DM-radiation interactions and compare the results to a traditional calculation in which DM only interacts gravitationally. Significant differences arise due to the presence of interactions, in terms of the number of low-mass DM haloes and their properties, such as their spin and density profile. These differences are clearly seen even for haloes more massive than the scale on which density fluctuations are suppressed. We also show that semi-analytical descriptions of the matter distribution in the non-linear regime fail to reproduce our numerical results, emphasizing the challenge of predicting structure formation in models with physics beyond collisionless DM.

astro-ph.CO↗

arXiv2014

A neutrino model fit to the CMB power spectrum

The standard cosmological model, LCDM, provides an excellent fit to Cosmic Microwave Background (CMB) data. However, the model has well known problems. For example, the cosmological constant, is fine-tuned to 1 part in 10^100 and the cold dark matter (CDM) particle is not yet detected in the laboratory. Shanks previously investigated a model which assumed neither exotic particles nor a cosmological constant but instead postulated a low Hubble constant (H_0) to allow a baryon density compatible with inflation and zero spatial curvature. However, recent Planck results make it more difficult to reconcile such a model with CMB power spectra. Here we relax the previous assumptions to assess the effects of assuming three active neutrinos of mass ~5eV. If we assume a low H_0~45kms^-1Mpc^-1 then, compared to the previous purely baryonic model, we find a significantly improved fit to the first 3 peaks of the Planck power spectrum. Nevertheless, the goodness-of-fit is still significantly worse than for LCDM and would require appeal to unknown systematic effects for the fit ever to be considered acceptable. A further serious problem is that the amplitude of fluctuations is low (sigma_8~0.2) making it difficult to form galaxies by the present day. This might then require seeds, perhaps from a primordial magnetic field, to be invoked for galaxy formation. These and other problems demonstrate the difficulties faced by models other than LCDM in fitting ever more precise cosmological data.

astro-ph.CO↗

arXiv2014

Using the Milky Way satellites to study interactions between cold dark matter and radiation

The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, taken at face value, the model significantly overestimates the number of satellite galaxies around the Milky Way. Attempts to solve this problem remain open to debate and have even led some to abandon CDM altogether. However, current simulations are limited by the assumption that dark matter feels only gravity. Here, we show that including interactions between CDM and radiation (photons or neutrinos) leads to a dramatic reduction in the number of satellite galaxies, alleviating the Milky Way satellite problem and indicating that physics beyond gravity may be essential to make accurate predictions of structure formation on small scales. The methodology introduced here gives constraints on dark matter interactions that are significantly improved over those from the cosmic microwave background.

astro-ph.CO↗