38 research outputs found
DarkHistory: A code package for calculating modified cosmic ionization and thermal histories with dark matter and other exotic energy injections
We present a new public Python package, DarkHistory, for computing the
effects of dark matter annihilation and decay on the temperature and ionization
history of the early universe. DarkHistory simultaneously solves for the
evolution of the free electron fraction and gas temperature, and for the
cooling of annihilation/decay products and the secondary particles produced in
the process. Consequently, we can self-consistently include the effects of both
astrophysical and exotic sources of heating and ionization, and automatically
take into account backreaction, where modifications to the
ionization/temperature history in turn modify the energy-loss processes for
injected particles. We present a number of worked examples, demonstrating how
to use the code in a range of different configurations, in particular for
arbitrary dark matter masses and annihilation/decay final states. Possible
applications of DarkHistory include mapping out the effects of dark matter
annihilation/decay on the global 21cm signal and the epoch of reionization, as
well as the effects of exotic energy injections other than dark matter
annihilation/decay. The code is available at
https://github.com/hongwanliu/DarkHistory with documentation at
https://darkhistory.readthedocs.io . Data files required to run the code can be
downloaded at https://doi.org/10.7910/DVN/DUOUWA .Comment: 40 pages, 17 figure
Exotic energy injection in the early universe II: CMB spectral distortions and constraints on light dark matter
We calculate the post-recombination contribution to the Cosmic Microwave
Background (CMB) spectral distortion due to general exotic energy injections,
including dark matter (DM) decaying or annihilating to Standard Model
particles. Upon subtracting the background distortion that would be present
even without such energy injections, we find residual distortions that are
still potentially large enough to be detectable by future experiments such as
PIXIE. The distortions also have a high-energy spectral feature that is a
unique signature of the injection of high-energy particles. We present a
calculation of the global ionization history in the presence of decaying dark
matter with sub-keV masses, and also show that previous calculations of the
global ionization history in the presence of energy injection are not
significantly modified by these additional spectral distortions. Our improved
treatment of low-energy electrons allows us to extend calculations of the CMB
anisotropy constraints for decaying DM down to arbitrarily low masses. We also
recast these bounds as constraints on the coupling of axion-like particles to
photons.Comment: 23 pages, 16 figure
Role of Cationic Side Chains in the Antimicrobial Activity of C18G.
Antimicrobial peptides (AMPs) have been an area of great interest, due to the high selectivity of these molecules toward bacterial targets over host cells and the limited development of bacterial resistance to these molecules throughout evolution. The peptide C18G has been shown to be a selective, broad spectrum AMP with a net +8 cationic charge from seven lysine residues in the sequence. In this work, the cationic Lys residues were replaced with other natural or non-proteinogenic cationic amino acids: arginine, histidine, ornithine, or diaminopropionic acid. These changes vary in the structure of the amino acid side chain, the identity of the cationic moiety, and the pKa of the cationic group. Using a combination of spectroscopic and microbiological methods, the influence of these cationic groups on membrane binding, secondary structure, and antibacterial activity was investigated. The replacement of Lys with most other cationic residues had, at most, 2-fold effects on minimal inhibitory concentration against a variety of Gram-positive and Gram-negative bacteria. However, the peptide containing His as the cationic group showed dramatically reduced activity. All peptide variants retained the ability to bind lipid vesicles and showed clear preference for binding vesicles that contained anionic lipids. Similarly, all peptides adopted a helical conformation when bound to lipids or membrane mimetics, although the peptide containing diaminopropionic acid exhibited a decreased helicity. The peptides exhibited a wider variety of activity in the permeabilization of bacterial membranes, with peptides containing Lys, Arg, or Orn being the most broadly active. In all, the antibacterial activity of the C18G peptide is generally tolerant to changes in the structure and identity of the cationic amino acids, yielding new possibilities for design and development of AMPs that may be less susceptible to immune and bacterial recognition or in vivo degradation
Stellar Diameters and Temperatures VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs
We present direct radii measurements of the well-known transiting exoplanet
host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We
find the limb-darkened angular diameters to be theta_LD = 0.3848 +/- 0.0055 and
0.2254 +/- 0.0072 milliarcsec for HD 189733 and HD 209458, respectively. HD
189733 and HD 209458 are currently the only two transiting exoplanet systems
where detection of the respective planetary companion's orbital motion from
high resolution spectroscopy has revealed absolute masses for both star and
planet. We use our new measurements together with the orbital information from
radial velocity and photometric time series data, Hipparcos distances, and
newly measured bolometric fluxes to determine the stellar effective
temperatures (T_eff = 4875 +/- 43, 6093 +/- 103 K), stellar linear radii (R_* =
0.805 +/- 0.016, 1.203 +/- 0.061 R_sun), mean stellar densities (rho_* = 1.62
+/- 0.11, 0.58 +/- 0.14 rho_sun), planetary radii (R_p = 1.216 +/- 0.024, 1.451
+/- 0.074 R_Jup), and mean planetary densities (rho_p = 0.605 +/- 0.029, 0.196
+/- 0.033 rho_Jup) for HD 189733 b and HD 209458 b, respectively. The stellar
parameters for HD 209458, a F9 dwarf, are consistent with indirect estimates
derived from spectroscopic and evolutionary modeling. However, we find that
models are unable to reproduce the observational results for the K2 dwarf, HD
189733. We show that, for stellar evolutionary models to match the observed
stellar properties of HD 189733, adjustments lowering the solar-calibrated
mixing length parameter from 1.83 to 1.34 need to be employed
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie