2,249 research outputs found
Bipyrimidine Signatures as a Photoprotective Genome Strategy in G+C-rich Halophilic Archaea
Halophilic Archaea
• Experience high levels of ultraviolet (UV) radiation in their environments
• Demonstrate high resistance to UV • Are protected by pigmentation and efficient DNA repair
• Have high genomic G+C conten
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Electron ionization via dark matter-electron scattering and the Migdal effect
There are currently several existing and proposed experiments designed to probe sub-GeV dark matter (DM) using electron ionization in various materials. The projected signal rates for these experiments assume that this ionization yield arises only from DM scattering directly off electron targets, ignoring secondary ionization contributions from DM scattering off nuclear targets. We investigate the validity of this assumption and show that if sub-GeV DM couples with comparable strength to both protons and electrons, as would be the case for a dark photon mediator, the ionization signal from atomic scattering via the Migdal effect scales with the atomic number and 3-momentum transfer as . The result is that the Migdal effect is always subdominant to electron scattering when the mediator is light, but that Migdal-induced ionization can dominate over electron scattering for heavy mediators and DM masses in the hundreds of MeV range. We put these two ionization processes on identical theoretical footing, address some theoretical uncertainties in the choice of atomic wave functions used to compute rates, and discuss the implications for DM scenarios where the Migdal process dominates, including for XENON10, XENON100, and the recent XENON1T results on light DM scattering
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Dark matter interpretation of excesses in multiple direct detection experiments
We present a novel unifying interpretation of excess event rates observed in several dark matter direct-detection experiments that utilize single-electron threshold semiconductor detectors. Despite their different locations, exposures, readout techniques, detector composition, and operating depths, these experiments all observe statistically significant excess event rates of . However, none of these persistent excesses has yet been reported as a dark matter signal because individually, each can be attributed to different well-motivated but unmodeled backgrounds, and taken together, they cannot be explained by dark matter particles scattering elastically off detector nuclei or electrons. We show that these results can be reconciled if the semiconductor detectors are seeing a collective inelastic process, consistent with exciting a plasmon. We further show that plasmon excitation could arise in two compelling dark matter scenarios, both of which can explain rates of existing signal excesses in germanium and, at least at the order of magnitude level, across several single-electron threshold detectors. At least one of these scenarios also yields the correct relic density from thermal freeze-out. Both dark matter scenarios motivate a radical rethinking of the standard interpretations of dark matter-electron scattering from recent experiments
The Quantum Transverse Field Ising Model on an Infinite Tree from Matrix Product States
We give a generalization to an infinite tree geometry of Vidal's infinite
time-evolving block decimation (iTEBD) algorithm for simulating an infinite
line of quantum spins. We numerically investigate the quantum Ising model in a
transverse field on the Bethe lattice using the Matrix Product State ansatz. We
observe a second order phase transition, with certain key differences from the
transverse field Ising model on an infinite spin chain. We also investigate a
transverse field Ising model with a specific longitudinal field. When the
transverse field is turned off, this model has a highly degenerate ground state
as opposed to the pure Ising model whose ground state is only doubly
degenerate.Comment: 28 pages, 23 figures, PDFlate
Strong-coupling approach to the Mott--Hubbard insulator on a Bethe lattice in Dynamical Mean-Field Theory
We calculate the Hubbard bands for the half-filled Hubbard model on a Bethe
lattice with infinite coordination number up to and including third order in
the inverse Hubbard interaction. We employ the Kato--Takahashi perturbation
theory to solve the self-consistency equation of the Dynamical Mean-Field
Theory analytically for the single-impurity Anderson model in multi-chain
geometry. The weight of the secondary Hubbard sub-bands is of fourth order so
that the two-chain geometry is sufficient for our study. Even close to the
Mott--Hubbard transition, our results for the Mott--Hubbard gap agree very well
with those from numerical Dynamical Density-Matrix Renormalization Group
(DDMRG) calculations. The density of states of the lower Hubbard band also
agrees very well with DDMRG data, apart from a resonance contribution at the
upper band edge which cannot be reproduced in low-order perturbation theory.Comment: 40 pages, 7 figure
Prospects for studying the mass and gas in protoclusters with future CMB observations
Protoclusters are the progenitors of massive galaxy clusters. Understanding
the properties of these structures is important for building a complete picture
of cluster formation and for understanding the impact of environment on galaxy
evolution. Future cosmic microwave background (CMB) surveys may provide insight
into the properties of protoclusters via observations of the thermal Sunyaev
Zel'dovich (SZ) effect and gravitational lensing. Using realistic
hydrodynamical simulations of protoclusters from the Three Hundred Project, we
forecast the ability of CMB Stage 4-like (CMB-S4) experiments to detect and
characterize protoclusters with observations of these two signals. For
protoclusters that are the progenitors of clusters at with we find that the S4-Ultra deep survey has a roughly
20% chance of detecting the main halos in these structures with
at and a 10% chance of detecting them at , where these
probabilities include the impacts of noise, CMB foregrounds, and the different
possible evolutionary histories of the structures. On the other hand, if
protoclusters can be identified using alternative means, such as via galaxy
surveys like LSST and Euclid, CMB-S4 will be able to obtain high
signal-to-noise measurements of their stacked lensing and SZ signals, providing
a way to measure their average mass and gas content. With a sample of 2700
protoclusters at , the CMB-S4 wide survey can measure the stacked SZ
signal with a signal-to-noise of 7.2, and the stacked lensing signal with a
signal-to-noise of 5.7. Future CMB surveys thus offer exciting prospects for
understanding the properties of protoclusters.Comment: 12 pages, 10 figure
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