399 research outputs found
Direct Detection is testing Freeze-in
Dark Matter (DM) may belong to a hidden sector that is only feebly
interacting with the Standard Model (SM) and may have never been in thermal
equilibrium in the Early Universe. In this case, the observed abundance of dark
matter particles could have built up through a process known as Freeze-in. We
show that, for the first time, direct detection experiments are testing this DM
production mechanism. This applies to scenarios where the SM and hidden sectors
communicate through a light mediator particle of mass less than a few MeV.
Through the exchange of such light mediator, the very same FIMP candidates can
have self-interactions that are in the range required to address the small
scale structure issues of collisionless cold dark matter.Comment: 7 pages, 4 figures. References added. Discussion of further
constraints on parameters. Figures updated. Conclusions unchanged. Matches
published versio
Top-philic Vector-Like Portal to Scalar Dark Matter
We investigate the phenomenology of scalar singlet dark matter candidates
that couple dominantly to the Standard Model via a Yukawa interaction with the
top quark and a colored vector-like fermion. We estimate the viability of this
vector-like portal scenario with respect to the most recent bounds from dark
matter direct and indirect detection, as well as to dark matter and vector-like
mediator searches at colliders. Moreover, we take QCD radiative corrections
into account in all our theoretical calculations. This work complements
analyses related both to models featuring a scalar singlet coupled through a
vector-like portal to light quarks, and to scenarios in which the dark matter
is a Majorana singlet coupled to the Standard Model through scalar colored
particles (akin to simplified models inspired by supersymmetry). Our study puts
especially forward the complementarity of different search strategies from
different contexts, and we show that current experiments allow for testing dark
matter masses ranging up to 700 GeV and mediator masses ranging up to 6 TeV.Comment: 15 pages, 11 figures; version accepted by PR
Radiative corrections to vectorlike portal dark matter
A massive real scalar dark matter particle can couple to Standard Model
leptons or quarks through a vector-like fermionic mediator , a scenario
known as the Vector-like portal. Due to helicity suppression of the
annihilation cross section into a pair of SM fermions, it has been shown in
previous works that radiative corrections, either at one-loop or through
radiation of gauge bosons, may play a significant role both in determining the
relic abundance and for indirect detection. All previous works considered the
limit of massless final state quarks or leptons. In this work, we focus on a
technical issue, which is to reliably determine the annihilation cross sections
taking into account finite fermion masses. Following previous works in the
framework of simplified supersymmetric dark matter scenarios, and building on
an analogy with Higgs decay into fermions, we address the issue of infrared and
collinear divergences that plagues the cross section by adopting an effective
operator description, which captures most of the relevant physics and give
explicit expressions for the annihilation cross sections. We then develop
several approximations for the differential and total cross sections, which
simplify greatly their expressions, and which can then be used in various
phenomenological studies of similar models. Finally, we describe our method to
compute the final gamma-ray spectrum, including hadronisation of the heavy
fermions, and provide some illustrative spectra for specific dark matter
candidates.Comment: 25 pages, 12 figures. One extra figure. Conclusions unchanged.
Version published in PR
Gentlest ascent dynamics on manifolds defined by adaptively sampled point-clouds
Finding saddle points of dynamical systems is an important problem in
practical applications such as the study of rare events of molecular systems.
Gentlest ascent dynamics (GAD) is one of a number of algorithms in existence
that attempt to find saddle points in dynamical systems. It works by deriving a
new dynamical system in which saddle points of the original system become
stable equilibria. GAD has been recently generalized to the study of dynamical
systems on manifolds (differential algebraic equations) described by equality
constraints and given in an extrinsic formulation. In this paper, we present an
extension of GAD to manifolds defined by point-clouds, formulated using the
intrinsic viewpoint. These point-clouds are adaptively sampled during an
iterative process that drives the system from the initial conformation
(typically in the neighborhood of a stable equilibrium) to a saddle point. Our
method requires the reactant (initial conformation), does not require the
explicit constraint equations to be specified, and is purely data-driven
Improving the Efficiency of Inductive Logic Programming Through the Use of Query Packs
Inductive logic programming, or relational learning, is a powerful paradigm
for machine learning or data mining. However, in order for ILP to become
practically useful, the efficiency of ILP systems must improve substantially.
To this end, the notion of a query pack is introduced: it structures sets of
similar queries. Furthermore, a mechanism is described for executing such query
packs. A complexity analysis shows that considerable efficiency improvements
can be achieved through the use of this query pack execution mechanism. This
claim is supported by empirical results obtained by incorporating support for
query pack execution in two existing learning systems
Interventricular Differences in β‐Adrenergic Responses in the Canine Heart: Role of Phosphodiesterases
Background
RV and LV have different embryologic, structural, metabolic, and electrophysiologic characteristics, but whether interventricular differences exist in β‐adrenergic (β‐AR) responsiveness is unknown. In this study, we examine whether β‐AR response and signaling differ in right (RV) versus left (LV) ventricles.
Methods and Results
Sarcomere shortening, Ca2+ transients, ICa,L and IKs currents were recorded in isolated dog LV and RV midmyocytes. Intracellular [cAMP] and PKA activity were measured by live cell imaging using FRET‐based sensors. Isoproterenol increased sarcomere shortening ≈10‐fold and Ca2+‐transient amplitude ≈2‐fold in LV midmyocytes (LVMs) versus ≈25‐fold and ≈3‐fold in RVMs. FRET imaging using targeted Epac2camps sensors revealed no change in subsarcolemmal [cAMP], but a 2‐fold higher β‐AR stimulation of cytoplasmic [cAMP] in RVMs versus LVMs. Accordingly, β‐AR regulation of ICa,L and IKs were similar between LVMs and RVMs, whereas cytoplasmic PKA activity was increased in RVMs. Both PDE3 and PDE4 contributed to the β‐AR regulation of cytoplasmic [cAMP], and the difference between LVMs and RVMs was abolished by PDE3 inhibition and attenuated by PDE4 inhibition. Finally LV and RV intracavitary pressures were recorded in anesthetized beagle dogs. A bolus injection of isoproterenol increased RV dP/dtmax≈5‐fold versus 3‐fold in LV.
Conclusion
Canine RV and LV differ in their β‐AR response due to intrinsic differences in myocyte β‐AR downstream signaling. Enhanced β‐AR responsiveness of the RV results from higher cAMP elevation in the cytoplasm, due to a decreased degradation by PDE3 and PDE4 in the RV compared to the LV
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