5 research outputs found
Projected Constraints on Modified Gravity Cosmologies from 21 cm Intensity Mapping
We present projected constraints on modified gravity models from the
observational technique known as 21 cm intensity mapping, where cosmic
structure is detected without resolving individual galaxies. The resulting map
is sensitive to both BAO and weak lensing, two of the most powerful
cosmological probes. It is found that a 200 m x 200 m cylindrical telescope,
sensitive out to z=2.5, would be able to distinguish DGP from most dark energy
models, and constrain the Hu & Sawicki f(R) model to |f_{R0}| < 9*10^(-6) at
95% confidence. The latter constraint makes extensive use of the lensing
spectrum in the nonlinear regime. These results show that 21 cm intensity
mapping is not only sensitive to modifications of the standard model's
expansion history, but also to structure growth. This makes intensity mapping a
powerful and economical technique, achievable on much shorter time scales than
optical experiments that would probe the same era.Comment: 10 pages, 5 figures, 1 table. Added references and expanded
discussion. As resubmitted to Phys. Rev. D, in response to reviewer comment
Near term measurements with 21 cm intensity mapping: neutral hydrogen fraction and BAO at z<2
It is shown that 21 cm intensity mapping could be used in the near term to
make cosmologically useful measurements. Large scale structure could be
detected using existing radio telescopes, or using prototypes for dedicated
redshift survey telescopes. This would provide a measure of the mean neutral
hydrogen density, using redshift space distortions to break the degeneracy with
the linear bias. We find that with only 200 hours of observing time on the
Green Bank Telescope, the neutral hydrogen density could be measured to 25%
precision at redshift 0.54<z<1.09. This compares favourably to current
measurements, uses independent techniques, and would settle the controversy
over an important parameter which impacts galaxy formation studies. In
addition, a 4000 hour survey would allow for the detection of baryon acoustic
oscillations, giving a cosmological distance measure at 3.5% precision. These
observation time requirements could be greatly reduced with the construction of
multiple pixel receivers. Similar results are possible using prototypes for
dedicated cylindrical telescopes on month time scales, or SKA pathfinder
aperture arrays on day time scales. Such measurements promise to improve our
understanding of these quantities while beating a path for future generations
of hydrogen surveys.Comment: 6 pages, 5 figures. Submitted to Phys. Rev. D. Addressed reviewer
comments. Changed figure format, added more detailed technical discussion,
and added forecasts for aperture arrays. Added references
Looking in the axion mirror: An all-sky analysis of stimulated decay
Axion dark matter (DM) produces echo images of bright radio sources via
stimulated decay. These images appear as a faint radio line centered at half
the axion mass, with the line width set by the DM velocity dispersion. Due to
the kinematics of the decay, the echo can be emitted in the direction nearly
opposite to the incoming source of stimulating radiation, meaning that axions
effectively behave as imperfect monochromatic mirrors. We present an all-sky
analysis of axion DM-induced echo images using extragalactic radio point
sources, Galactic supernova remnants (SNRs), and Galactic synchrotron radiation
(GSR) as sources of stimulating radiation. The aggregate signal strength is not
significantly affected by unknown properties of individual sources of
stimulating radiation, which we sample from an empirical distribution to
generate an ensemble of realizations for the all-sky signal template. We
perform forecasts for CHIME, HERA, CHORD, HIRAX, and BURSTT, finding that they
can run as competitive axion experiments simultaneously with other objectives,
requiring no new hardware.Comment: 24 pages, 15 figures. Supplementary code and animation at
https://github.com/yitiansun/axion-mirro