15 research outputs found
Non-Abelian dark matter and dark radiation
We propose a new class of dark matter models with unusual phenomenology. What
is ordinary about our models is that dark matter particles are WIMPs, they are
weakly coupled to the Standard Model and have weak scale masses. What is
unusual is that they come in multiplets of a new "dark" non-Abelian gauge group
with milli-weak coupling. The massless dark gluons of this dark gauge group
contribute to the energy density of the universe as a form of weakly
self-interacting dark radiation. In this paper we explore the consequences of
having i.) dark matter in multiplets ii.) self-interacting dark radiation and
iii.) dark matter which is weakly coupled to dark radiation. We find that i.)
dark matter cross sections are modified by multiplicity factors which have
significant consequences for collider searches and indirect detection, ii.)
dark gluons have thermal abundances which affect the CMB as dark radiation.
Unlike additional massless neutrino species the dark gluons are interacting and
have vanishing viscosity and iii.) the coupling of dark radiation to dark
matter represents a new mechanism for damping the large scale structure power
spectrum. A combination of additional radiation and slightly damped structure
is interesting because it can remove tensions between global CDM fits
from the CMB and direct measurements of the Hubble expansion rate () and
large scale structure ().Comment: 25 pages, 8 figures; v2: minor improvements, references added; v3:
added references and an acknowledgement note to J. Lesgourgues; accepted for
publication in PR
Interacting Dark Sector and Precision Cosmology
We consider a recently proposed model in which dark matter interacts with a
thermal background of dark radiation. Dark radiation consists of relativistic
degrees of freedom which allow larger values of the expansion rate of the
universe today to be consistent with CMB data (-problem). Scattering
between dark matter and radiation suppresses the matter power spectrum at small
scales and can explain the apparent discrepancies between CDM
predictions of the matter power spectrum and direct measurements of Large Scale
Structure LSS (-problem). We go beyond previous work in two ways: 1.
we enlarge the parameter space of our previous model and allow for an arbitrary
fraction of the dark matter to be interacting and 2. we update the data sets
used in our fits, most importantly we include LSS data with full -dependence
to explore the sensitivity of current data to the shape of the matter power
spectrum. We find that LSS data prefer models with overall suppressed matter
clustering due to dark matter - dark radiation interactions over CDM
at 3-4 . However recent weak lensing measurements of the power spectrum
are not yet precise enough to clearly distinguish two limits of the model with
different predicted shapes for the linear matter power spectrum. In two
Appendices we give a derivation of the coupled dark matter and dark radiation
perturbation equations from the Boltzmann equation in order to clarify a
confusion in the recent literature, and we derive analytic approximations to
the solutions of the perturbation equations in the two physically interesting
limits of all dark matter weakly interacting or a small fraction of dark matter
strongly interacting.Comment: 29 pages + 2 Appendices; published versio
Cannibal Dark Matter and Large Scale Structure
Cannibals are dark matter particles with a scattering process that allows
three particles to annihilate to two. This exothermic process keeps the gas of
the remaining particles warm long after they become non-relativistic. A
cannibalizing dark sector which is decoupled from the Standard Model naturally
arises from a pure-glue confining hidden sector. It has an effective field
theory description with a single massive interacting real scalar field, the
lightest glueball. Since warm dark matter strongly suppresses growth of
structure cannibals cannot be all of the dark matter. Thus we propose a
scenario where most dark matter is non-interacting and cold but about 1 percent
is cannibalistic. We review the cannibals' unusual scaling of the temperature
and energy and number densities with redshift and generalize the equations for
the growth of matter density perturbations to the case of cannibals. We solve
the equations numerically to predict the scaling of the Hubble parameter and
the characteristic shape of the linear matter power spectrum as a function of
model parameters. Our results may have implications for the and
problems.Comment: 25 pages, 1 appendix. v2: typos corrected, added reference
Probing New Physics with High-Redshift Quasars: Axions and Non-standard Cosmology
The Hubble diagram of quasars, as candidates to ``standardizable" candles,
has been used to measure the expansion history of the Universe at late times,
up to very high redshifts (). It has been shown that this history, as
inferred from the quasar dataset, deviates at level from the
concordance (CDM) cosmology model preferred by the cosmic microwave
background (CMB) and other datasets. In this article, we investigate whether
new physics beyond CDM (BCDM) or beyond the Standard Model
(BSM) could make the quasar data consistent with the concordance model. We
first show that an effective redshift-dependent relation between the quasar UV
and X-ray luminosities, complementing previous phenomenological work in the
literature, can potentially remedy the discrepancy. Such a redshift dependence
can be realized in a BSM model with axion-photon conversion in the
intergalactic medium (IGM), although the preferred parameter space could be in
mild tension with various other astrophysical constraints on axions, depending
on the specific assumptions made regarding the IGM magnetic field. We briefly
discuss a variation of the axion model that could evade these astrophysical
constraints. On the other hand, we show that models beyond CDM such as
one with a varying dark energy equation of state (CDM) or the
phenomenological cosmographic model with a polynomial expansion of the
luminosity distance, cannot alleviate the tension. The code for our analysis,
based on emcee and corner.py, is publicly available at
https://github.com/ChenSun-Phys/high_z_candles.Comment: 10+3 pages, 4 figures, 4 tables, 3 appendices; comments are welcom
Stepped Partially Acoustic Dark Matter: Likelihood Analysis and Cosmological Tensions
We generalize the recently proposed Stepped Partially Acoustic Dark Matter
(SPartAcous) model by including additional massless degrees of freedom in the
dark radiation sector. We fit SPartAcous and its generalization against
cosmological precision data from the cosmic microwave background, baryon
acoustic oscillations, large-scale structure, supernovae type Ia, and Cepheid
variables. We find that SPartAcous significantly reduces the tension but
does not provide any meaningful improvement of the tension, while the
generalized model succeeds in addressing both tensions, and provides a better
fit than and other dark sector models proposed to address
the same tensions. In the generalized model, can be raised to
(the 95% upper limit) if the fitted data does not
include the direct measurement from the SH0ES collaboration, and to
(95% upper limit) if it does. A version of
that has been modified to analyze this model is publicly
available at https://github.com/ManuelBuenAbad/class_spartacousComment: 38 pages, 8 figure