1,546 research outputs found
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
Minimal Asymmetric Dark Matter
In the early Universe, any particle carrying a conserved quantum number and
in chemical equilibrium with the thermal bath will unavoidably inherit a
particle-antiparticle asymmetry. A new particle of this type, if stable, would
represent a candidate for asymmetric dark matter (DM) with an asymmetry
directly related to the baryon asymmetry. We study this possibility for a
minimal DM sector constituted by just one (generic) multiplet
carrying hypercharge, assuming that at temperatures above the electroweak phase
transition an effective operator enforces chemical equilibrium between
and the Higgs boson. We argue that limits from DM direct detection searches
severely constrain this scenario, leaving as the only possibilities scalar or
fermion multiplets with hypercharge , preferentially quintuplets or
larger representations, and with a mass in the few TeV range.Comment: 9 pages, 2 figures, included t-channel scattering, added details on
charged-neutral mass splitting and indirect detection, accepted in PL
Higher Dimensional Effective Operators for Direct Dark Matter Detection
We discuss higher dimensional effective operators describing interactions
between fermionic dark matter and Standard Model particles. They are typically
suppressed compared to the leading order effective operators, which can explain
why no conclusive direct dark matter detection has been made so far. The
ultraviolet completions of the effective operators, which we systematically
study, require new particles. These particles can potentially have masses at
the TeV scale and can therefore be phenomenologically interesting for LHC
physics. We demonstrate that the lowest order options require Higgs-portal
interactions generated by dimension six operators. We list all possible
tree-level completions with extra fermions and scalars, and we discuss the LHC
phenomenology of a specific example with extra heavy fermion doublets.Comment: 27 pages, 11 figures, 3 table
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
Neutrino mass from higher than d=5 effective operators in SUSY, and its test at the LHC
We discuss neutrino masses from higher than d=5 effective operators in a
supersymmetric framework, where we explicitly demonstrate which operators could
be the leading contribution to neutrino mass in the MSSM and NMSSM. As an
example, we focus on the d=7 operator L L H_u H_u H_d H_u, for which we
systematically derive all tree-level decompositions. We argue that many of
these lead to a linear or inverse see-saw scenario with two extra neutral
fermions, where the lepton number violating term is naturally suppressed by a
heavy mass scale when the extra mediators are integrated out. We choose one
example, for which we discuss possible implementations of the neutrino flavor
structure. In addition, we show that the heavy mediators, in this case SU(2)
doublet fermions, may indeed be observable at the LHC, since they can be
produced by Drell-Yan processes and lead to displaced vertices when they decay.
However, the direct observation of lepton number violating processes is on the
edge at LHC.Comment: 24 pages, 5 figures, 6 table
Dark Matter interactions in an flavor symmetry framework
The interactions of dark matter (DM) with the visible sector are often
phenomenologically described in the framework of simplified models where the
couplings of quarks to the new particles are generally assumed to be universal
or have a simple structure motivated by observational benchmarks. They should,
however, a priori be treated as free parameters. In this work we discuss one
particular realization of the structure of DM couplings based on an flavor symmetry, which has been shown to account reasonably well for
fermion masses and mixing, and compare their effect on observational signals to
universal as well as Yukawa-like couplings, which are motivated by minimal
flavor violation. We will also comment on how these structures could be
constrained in UV complete theories of DM and how DM observables, such as,
e.g., relic density and direct detection, can potentially be used as a smoking
gun for the underlying flavor symmetries.Comment: 24 pages, 6 figure
Functional lesional neurosurgery for tremor: back to the future?
For nearly a century, functional neurosurgery has been applied in the treatment of tremor. While deep brain stimulation has been in the focus of academic interest in recent years, the establishment of incisionless technology, such as MRI-guided high-intensity focused ultrasound, has again stirred interest in lesional approaches.In this article, we will discuss the historical development of surgical technique and targets, as well as the technological state-of-the-art of conventional and incisionless interventions for tremor due to Parkinson's disease, essential and dystonic tremor and tremor related to multiple sclerosis (MS) and midbrain lesions. We will also summarise technique-inherent advantages of each technology and compare their lesion characteristics. From this, we identify gaps in the current literature and derive future directions for functional lesional neurosurgery, in particularly potential trial designs, alternative targets and the unsolved problem of bilateral lesional treatment. The results of a systematic review and meta-analysis of the consistency, efficacy and side effect rate of lesional treatments for tremor are presented separately alongside this article
Pion Cloud Contribution to K+ Nucleus Scattering
A careful reanalysis is done of the contribution to nucleus
scattering from the interaction of the kaon with the virtual pion cloud. The
usual approximations made in the evaluation of the related kaon selfenergy are
shown to fail badly. We also find new interaction mechanisms which provide
appreciable corrections to the kaon selfenergy. Some of these contribute to the
imaginary part below pion creation threshold. The inclusion of these new
mechanisms in the inelastic part of the optical potential produces a
significant improvement in the differential and total nuclear cross
sections. Uncertainties remain in the dispersive part of the optical potential.Comment: 27 pages, 17 figures (not all of them included, please request them),
report UG-DFM-2/9
The Tensor to Scalar Ratio of Phantom Dark Energy Models
We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.Comment: 5 pages, 4 figure
Contribution of Long Wavelength Gravitational Waves to the CMB Anisotropy
We present an in depth discussion of the production of gravitational waves
from an inflationary phase that could have occurred in the early universe,
giving derivations for the resulting spectrum and energy density. We also
consider the large-scale anisotropy in the cosmic microwave background
radiation coming from these waves. Assuming that the observed quadrupole
anisotropy comes mostly from gravitational waves (consistent with the
predictions of a flat spectrum of scalar density perturbations and the measured
dipole anisotropy) we describe in detail how to derive a value for the scale of
inflation of GeV, which is at a particularly interesting
scale for particle physics. This upper limit corresponds to a 95\% confidence
level upper limit on the scale of inflation assuming only that the quadrupole
anisotropy from gravitational waves is not cancelled by another source. Direct
detection of gravitational waves produced by inflation near this scale will
have to wait for the next generation of detectors.Comment: (LaTeX 16 pages), 2 figures not included, YCTP-P16-9
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