12,834 research outputs found
Empirical ugri-UBVRc Transformations for Galaxies
We present empirical color transformations between Sloan Digital Sky Survey
ugri and Johnson-Cousins UBVRc photometry for nearby galaxies (D < 11 Mpc). We
use the Local Volume Legacy (LVL) galaxy sample where there are 90 galaxies
with overlapping observational coverage for these two filter sets. The LVL
galaxy sample consists of normal, non-starbursting galaxies. We also examine
how well the LVL galaxy colors are described by previous transformations
derived from standard calibration stars and model-based galaxy templates. We
find significant galaxy color scatter around most of the previous
transformation relationships. In addition, the previous transformations show
systematic offsets between transformed and observed galaxy colors which are
visible in observed color-color trends. The LVL-based transformations
show no systematic color offsets and reproduce the observed color-color galaxy
trends.Comment: Accepted for publication in MNRAS (9 pages, 6 figures, 4 tables
Minimal self-interacting dark matter models with light mediator
The light mediator scenario of self-interacting dark matter is strongly
constrained in many ways. After summarizing the various constraints, we discuss
minimal options and models which allow to nevertheless satisfy all these
constraints. One straightforward possibility arises if the dark matter and
light mediator particles have a temperature sizably smaller than the SM
particles. Another simple possibility arises if dark matter doesn't annihilate
dominantly into a pair of light mediators but into heavier particles. Both
possibilities are discussed with scalar as well as vector boson light
mediators. Further possibilities, such as with a hierarchy of quartic scalar
couplings, are also identified.Comment: 23 pages, 31 figures, accepted for publication in JCA
Robust Estimators in Generalized Pareto Models
This paper deals with optimally-robust parameter estimation in generalized
Pareto distributions (GPDs). These arise naturally in many situations where one
is interested in the behavior of extreme events as motivated by the
Pickands-Balkema-de Haan extreme value theorem (PBHT). The application we have
in mind is calculation of the regulatory capital required by Basel II for a
bank to cover operational risk. In this context the tail behavior of the
underlying distribution is crucial. This is where extreme value theory enters,
suggesting to estimate these high quantiles parameterically using, e.g. GPDs.
Robust statistics in this context offers procedures bounding the influence of
single observations, so provides reliable inference in the presence of moderate
deviations from the distributional model assumptions, respectively from the
mechanisms underlying the PBHT.Comment: 26pages, 6 figure
Content analysis of the South African MMed mini-dissertation
Background. There is no baseline information on the South African (SA) MMed mini-dissertation, which became a compulsory (and controversial) research component for specialist registration in 2011.Objective. To obtain evidence-based information regarding the current composition of the research output of the MMed mini-dissertation.Methods. SA MMed mini-dissertations (N=307) were downloaded from electronic theses and dissertation websites and 8 university repositories that provide specialist training. Fourteen variables were noted for each mini-dissertation, the data were entered into an Excel (2016) (Microsoft, USA) spreadsheet and analysed using descriptive statistics.Results. The 307 mini-dissertations, representing 24 of the Colleges of Medicine of SA, were submitted from 1996 to 2018, mainly in monograph format (76%) and almost equally divided between prospective and retrospective studies. Observational studies predominated, with meta-analyses, systematic reviews and randomised controlled trials comprising 5% of the sample. Although quantitative investigations dominated (82%), just less than half of these used statistics to test variables. Confirmed ethical compliance improved from 41% in pre-2011 dissertations to 83% for dissertations submitted during 2015 - 2018.Conclusions. This study provides descriptive data on the SA MMed mini-dissertation. Comparisons indicate that the MMed research component compares favourably with the content and research approach of similar international specialist trainee research outputs
Impact of a XENONnT Signal on LHC Dijet Searches
It is well-known that dark matter (DM) direct detection experiments and the
LHC are complementary, since they probe physical processes occurring at
different energy scales. And yet, there are aspects of this complementarity
which are still not fully understood, or exploited. For example, what is the
impact that the discovery of DM at XENONnT would have on present and future
searches for DM in LHC final states involving a pair of hadronic jets? In this
work we investigate the impact of a XENONnT signal on the interpretation of
current dijet searches at the LHC, and on the prospects for dijet signal
discovery at the High-Luminosity (HL) LHC in the framework of simplified
models. Specifically, we focus on a general class of simplified models where DM
can have spin 0, 1/2 or 1, and interacts with quarks through the exchange of a
scalar, pseudo-scalar, vector, or pseudo-vector mediator. We find that
exclusion limits on the mediator's mass and its coupling to quarks from dijet
searches at the LHC are significantly affected by a signal at XENONnT, and that
signal events at XENONnT would drastically narrow the region
in the parameter space of simplified models where a dijet signal can be
discovered at C.L. at the HL-LHC.Comment: 23 pages, 3 figures, 3 tables, version accepted by JHE
Collide and Conquer: Constraints on Simplified Dark Matter Models using Mono-X Collider Searches
The use of simplified models as a tool for interpreting dark matter collider
searches has become increasingly prevalent, and while early Run II results are
beginning to appear, we look to see what further information can be extracted
from the Run I dataset. We consider three `standard' simplified models that
couple quarks to fermionic singlet dark matter: an -channel vector mediator
with vector or axial-vector couplings, and a -channel scalar mediator. Upper
limits on the couplings are calculated and compared across three alternate
channels, namely mono-jet, mono- (leptonic) and mono- (hadronic). The
strongest limits are observed in the mono-jet channel, however the
computational simplicity and absence of significant -channel model width
effects in the mono-boson channels make these a straightforward and competitive
alternative. We also include a comparison with relic density and direct
detection constraints.Comment: 32 pages, 8 figures; v2: minor changes, conclusion unchanged, matches
published versio
Determining Dark Matter properties with a XENONnT/LZ signal and LHC-Run3 mono-jet searches
We develop a method to forecast the outcome of the LHC Run 3 based on the
hypothetical detection of signal events at XENONnT. Our
method relies on a systematic classification of renormalisable single-mediator
models for dark matter-quark interactions, and is valid for dark matter
candidates of spin less than or equal to one. Applying our method to simulated
data, we find that at the end of the LHC Run 3 only two mutually exclusive
scenarios would be compatible with the detection of signal
events at XENONnT. In a first scenario, the energy distribution of the signal
events is featureless, as for canonical spin-independent interactions. In this
case, if a mono-jet signal is detected at the LHC, dark matter must have spin
1/2 and interact with nucleons through a unique velocity-dependent operator. If
a mono-jet signal is not detected, dark matter interacts with nucleons through
canonical spin-independent interactions. In a second scenario, the spectral
distribution of the signal events exhibits a bump at non zero recoil energies.
In this second case, a mono-jet signal can be detected at the LHC Run 3, dark
matter must have spin 1/2 and interact with nucleons through a unique
momentum-dependent operator. We therefore conclude that the observation of
signal events at XENONnT combined with the detection, or the
lack of detection, of a mono-jet signal at the LHC Run 3 would significantly
narrow the range of possible dark matter-nucleon interactions. As we argued
above, it can also provide key information on the dark matter particle spin.Comment: 17 pages, 8 figures, updated operator coefficients and figures,
version accepted by PR
Simplified Models for Dark Matter and Missing Energy Searches at the LHC
The study of collision events with missing energy as searches for the dark
matter (DM) component of the Universe are an essential part of the extensive
program looking for new physics at the LHC. Given the unknown nature of DM, the
interpretation of such searches should be made broad and inclusive. This report
reviews the usage of simplified models in the interpretation of missing energy
searches. We begin with a brief discussion of the utility and limitation of the
effective field theory approach to this problem. The bulk of the report is then
devoted to several different simplified models and their signatures, including
s-channel and t-channel processes. A common feature of simplified models for DM
is the presence of additional particles that mediate the interactions between
the Standard Model and the particle that makes up DM. We consider these in
detail and emphasize the importance of their inclusion as final states in any
coherent interpretation. We also review some of the experimental progress in
the field, new signatures, and other aspects of the searches themselves. We
conclude with comments and recommendations regarding the use of simplified
models in Run-II of the LHC.Comment: v2. references added, version submitted to journal. v1. 47 pages, 13
plot
Sensitivity of the Cherenkov Telescope Array to the detection of a dark matter signal in comparison to direct detection and collider experiments
Imaging atmospheric Cherenkov telescopes (IACTs) that are sensitive to
potential -ray signals from dark matter (DM) annihilation above
GeV will soon be superseded by the Cherenkov Telescope Array (CTA).
CTA will have a point source sensitivity an order of magnitude better than
currently operating IACTs and will cover a broad energy range between 20 GeV
and 300 TeV. Using effective field theory and simplified models to calculate
-ray spectra resulting from DM annihilation, we compare the prospects
to constrain such models with CTA observations of the Galactic center with
current and near-future measurements at the Large Hadron Collider (LHC) and
direct detection experiments. For DM annihilations via vector or pseudoscalar
couplings, CTA observations will be able to probe DM models out of reach of the
LHC, and, if DM is coupled to standard fermions by a pseudoscalar particle,
beyond the limits of current direct detection experiments.Comment: Accepted for publication in PRD. 20 pages, 11 figure
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