3,040 research outputs found
Triplet-Quadruplet Dark Matter
We explore a dark matter model extending the standard model particle content
by one fermionic triplet and two fermionic quadruplets,
leading to a minimal realistic UV-complete model of electroweakly interacting
dark matter which interacts with the Higgs doublet at tree level via two kinds
of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum
of the dark sector consists of three Majorana fermions, three singly charged
fermions, and one doubly charged fermion, with the lightest neutral fermion
serving as a dark matter candidate. A typical spectrum exhibits a
large degree of degeneracy in mass between the neutral and charged fermions,
and we examine the one-loop corrections to the mass differences to ensure that
the lightest particle is neutral. We identify regions of parameter space for
which the dark matter abundance is saturated for a standard cosmology,
including coannihilation channels, and find that this is typically achieved for
. Constraints from precision electroweak
measurements, searches for dark matter scattering with nuclei, and dark matter
annihilation are important, but leave open a viable range for a thermal relic.Comment: 27 pages, 6 figures. v2: minor revisions to match published versio
Valence Bond Entanglement and Fluctuations in Random Singlet Phases
The ground state of the uniform antiferromagnetic spin-1/2 Heisenberg chain
can be viewed as a strongly fluctuating liquid of valence bonds, while in
disordered chains these bonds lock into random singlet states on long length
scales. We show that this phenomenon can be studied numerically, even in the
case of weak disorder, by calculating the mean value of the number of valence
bonds leaving a block of contiguous spins (the valence-bond entanglement
entropy) as well as the fluctuations in this number. These fluctuations show a
clear crossover from a small regime, in which they behave similar to those
of the uniform model, to a large regime in which they saturate in a way
consistent with the formation of a random singlet state on long length scales.
A scaling analysis of these fluctuations is used to study the dependence on
disorder strength of the length scale characterizing the crossover between
these two regimes. Results are obtained for a class of models which include, in
addition to the spin-1/2 Heisenberg chain, the uniform and disordered critical
1D transverse-field Ising model and chains of interacting non-Abelian anyons.Comment: 8 pages, 6 figure
Low-momentum interactions with Brown-Rho-Ericson scalings and the density dependence of the nuclear symmetry energy
We have calculated the nuclear symmetry energy up to
densities of with the effects from the Brown-Rho (BR) and
Ericson scalings for the in-medium mesons included. Using the
low-momentum interaction with and without such scalings, the equations of state
(EOS) of symmetric and asymmetric nuclear matter have been calculated using a
ring-diagarm formalism where the particle-particle-hole-hole ring diagrams are
included to all orders. The EOS for symmetric nuclear matter and neutron matter
obtained with linear BR scaling are both overly stiff compared with the
empirical constraints of Danielewicz {\it et al.} \cite{daniel02}. In contrast,
satisfactory results are obtained by either using the nonlinear Ericson scaling
or by adding a Skyrme-type three-nucleon force (TNF) to the unscaled
interaction.
Our results for obtained with the nonlinear Ericson scaling
are in good agreement with the empirical values of Tsang {\it et al.}
\cite{tsang09} and Li {\it et al.} \cite{li05}, while those with TNF are
slightly below these values. For densities below the nuclear saturation density
, the results of the above calculations are nearly equivalent to each
other and all in satisfactory agreement with the empirical values.Comment: 7 pages, 6 figure
Defective hierarchical porous copper-based metal-organic frameworks synthesised via facile acid etching strategy
Introducing hierarchical pore structure to microporous materials such as
metal-organic frameworks (MOFs) can be beneficial for reactions where the rate
of reaction is limited by low rates of diffusion or high pressure drop. This
advantageous pore structure can be obtained by defect formation, mostly via
post-synthetic acid etching, which has been studied extensively on water-stable
MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a
corresponding manner by using phosphoric acid as a size-selective etching agent
and a mixture of dimethyl sulfoxide and methanol as a dilute solvent.
Interestingly, we demonstrate that the etching process which is time- and
acidity- dependent, can result in formation of defective HKUST-1 with extra
interconnected hexagonal macropores without compromising on the bulk
crystallinity. These findings suggest an intelligent scalable synthetic method
for formation of hierarchical porosity in MOFs that are prone to hydrolysis,
for improved molecular accessibility and diffusion for catalysis.Comment: 14 pages, 8 figure
Microbial ecology of Thiobacillus ferrooxidans
FINAL TECHNICAL REPORT
TO
U.S. DEPARTMENT OF THE INTERIOR
Geological Survey
Washington. D.C.The contents of this report were developed in part under a grant from
the Department of the Interior, U.S. Geological Survey. Grant number 14-08-0001-61313
- …