A
bstract
Hidden sectors are ubiquitous in supergravity theories, in strings and in branes. Well motivated models such as the Stueckelberg hidden sector model could provide a candidate for dark ...matter. In such models, the hidden sector communicates with the visible sector via the exchange of a dark photon (dark
Z
′) while dark matter is constituted of Dirac fermions in the hidden sector. Using data from collider searches and precision measurements of SM processes as well as the most recent limits from dark matter direct and indirect detection experiments, we perform a comprehensive scan over a wide range of the
Z
′ mass and set exclusion bounds on the parameter space from sub-GeV to several TeV. We then discuss the discovery potential of an
O
(TeV) scale
Z
′ at HL-LHC and the ability of future forward detectors to probe very weakly interacting sub-GeV
Z
′ bosons. Our analysis shows that the parameter space in which a
Z
′ can decay to hidden sector dark matter is severely constrained whereas limits become much weaker for a
Z
′ with no dark decays. The analysis also favors a self-thermalized dark sector which is necessary to satisfy the dark matter relic density.
We present simplified MSSM models for light neutralinos and charginos with realistic mass spectra and realistic gaugino-higgsino mixing, that can be used in experimental searches at the LHC. The ...formerly used naive approach of defining mass spectra and mixing matrix elements manually and independently of each other does not yield genuine MSSM benchmarks. We suggest the use of less simplified, but realistic MSSM models, whose mass spectra and mixing matrix elements are the result of a proper matrix diagonalisation. We propose a novel strategy targeting the design of such benchmark scenarios, accounting for user-defined constraints in terms of masses and particle mixing. We apply it to the higgsino case and implement a scan in the four relevant underlying parameters
{
μ
,
tan
β
,
M
1
,
M
2
}
for a given set of light neutralino and chargino masses. We define a measure for the quality of the obtained benchmarks, that also includes criteria to assess the higgsino content of the resulting charginos and neutralinos. We finally discuss the distribution of the resulting models in the MSSM parameter space as well as their implications for supersymmetric dark matter phenomenology.
A
bstract
We present a detailed study of a combined singlet-doublet scalar and singlet-doublet fermion model for dark matter. These models have only been studied separately in the past. We show that ...their combination allows for the radiative generation of neutrino masses, but that it also implies the existence of lepton-flavour violating (LFV) processes. We first analyse the dark matter, neutrino mass and LFV aspects separately. We then perform two random scans for scalar dark matter imposing Higgs mass, relic density and neutrino mass constraints, one over the full parameter space, the other over regions where scalar-fermion coannihilations become important. In the first case, a large part of the new parameter space is excluded by LFV, and the remaining models will be probed by XENONnT. In the second case, direct detection cross sections are generally too small, but a substantial part of the viable models will be tested by future LFV experiments. Possible constraints from the LHC are also discussed.
A
bstract
To maximise the information obtained from various independent new physics searches conducted at the LHC, it is imperative to consider the combination of multiple analyses. To showcase the ...exclusion power gained by combining signal regions from different searches, we consider a simplified scenario inspired by supersymmetry, with all particles but one squark flavour and a bino-like neutralino decoupled. The corresponding signal therefore comprises strong squark pair production, associated squark-neutralino production, as well as weak neutralino pair production. We find that considering the associated and strong production mechanisms together significantly impacts mass limits, while contributions from the weak production are insignificant in the context of current exclusion limits. In addition, we demonstrate that the combination of uncorrelated signal regions as assessed from the recent TACO approach substantially pushes exclusion limits towards higher masses, relative to the bounds derived from the most sensitive individual analyses.
It is shown that a decaying neutralino in a supergravity unified framework is a viable candidate for dark matter. Such a situation arises in the presence of a hidden sector with ultraweak couplings ...to the visible sector where the neutralino can decay into the hidden sector’s lightest supersymmetric particle (LSP) with a lifetime larger than the lifetime of the universe. We present a concrete model where the MSSM/SUGRA is extended to include a hidden sector comprised of
U
(
1
)
X
1
×
U
(
1
)
X
2
gauge sector and the LSP of the hidden sector is a neutralino which is lighter than the LSP neutralino of the visible sector. We compute the loop suppressed radiative decay of the visible sector neutralino into the neutralino of the hidden sector and show that the decay can occur with a lifetime larger than the age of the universe. The decaying neutralino can be probed by indirect detection experiments, specifically by its signature decay into the hidden sector neutralino and an energetic gamma ray photon. Such a gamma ray can be searched for with improved sensitivity at Fermi-LAT and by future experiments such as the Square Kilometer Array (SKA) and the Cherenkov Telescope Array (CTA). We present several benchmarks which have a natural suppression of the hadronic channels from dark matter annihilation and decays and consistent with measurements of the antiproton background.
We present
DM@NLO
, a
Fortran 77
based program with a
C++
interface dedicated to precision calculations of dark matter (DM) (co)annihilation cross-sections and elastic dark matter-nucleon scattering ...amplitudes in the minimal supersymmetric (SUSY) Standard Model (MSSM) at next-to-leading order (NLO) in perturbative (SUSY) QCD. If the annihilating initial particles carry an electric or colour charge, the Sommerfeld enhanced cross section is included as well and can be matched to the NLO cross section. We review these calculations including technical details relevant for using the code. We illustrate their impact by applying
DM@NLO
to an example scenario in the constrained MSSM.
A
bstract
Next-to-leading order predictions matched to parton showers are compared with recent ATLAS data on isolated photon production and CMS data on associated photon and jet production in pp and ...pPb collisions at different centre-of-mass energies of the LHC. We find good agreement and, as expected, considerably reduced scale uncertainties compared to previous theoretical calculations. Predictions are made for the ratio of inclusive photons over decay photons
R
γ
, an important quantity to evaluate the significance of additional photon sources, e.g. thermal radiation from a Quark-Gluon-Plasma, and for distributions in the parton momentum fraction in lead ions
x
Pb
obs
, that could be determined by ALICE, ATLAS, CMS and LHCb in ongoing analyses of photon+jet production in pPb collisions at
s
N
N
=
5.02
TeV. These data should have an important impact on the determination of nuclear effects such as shadowing at low
x
.
A
bstract
Motivated by the shift in experimental attention towards electroweak super-symmetric particle production at the CERN LHC, we update in this paper our precision predictions at ...next-to-leading order of perturbative QCD matched to resummation at the next-to-leading logarithmic accuracy for direct slepton pair production in proton-proton collisions. Simplified models, now commonly adopted by the experimental collaborations for selectrons and smuons as well as mixing staus, are used as benchmarks for total cross sections at achieved and future center-of-mass energies. They are presented together with the corresponding scale and parton density uncertainties in graphical and tabular form for future reference. Using modern Monte Carlo techniques, we also reanalyze recent ATLAS and CMS slepton searches in light of our precision cross sections and for various assumptions on the decomposition of the sleptons and their neutralino decay products.
Detection prospects of singlet fermionic dark matter Esch, Sonja; Klasen, Michael; Yaguna, Carlos E.
Physical review. D, Particles, fields, gravitation, and cosmology,
10/2013, Volume:
88, Issue:
7
Journal Article
Peer reviewed
Open access
A singlet fermion which interacts only with a new singlet scalar provides a viable and minimal scenario that can explain the dark matter. The singlet fermion is the dark matter particle whereas the ...new scalar mixes with the Higgs boson providing a link between the dark matter sector and the standard model. In this paper, we present an updated analysis of this model focused on its detection prospects. Both the parity-conserving case and the most general case are considered. First, the full parameter space of the model is analyzed, and the regions compatible with the dark matter constraint are obtained and characterized. Then, the implications of current and future direct detection experiments are taken into account. Specifically, we determine the regions of the multidimensional parameter space that are currently excluded and those that are going to be probed by next generation experiments. Finally, indirect detection prospects are discussed and the expected signal at neutrino telescopes is calculated.
A
bstract
The production of virtual photons is a very sensitive probe of the properties of the quark-gluon plasma. As they are experimentally detected by lepton pairs, they suffer from a large ...background arising from hadron decays. Light-flavour hadrons dominate at low invariant masses below
m
ee
~ 0.5 GeV and heavy flavours above. These contributions must therefore also be taken into account in experimental analyses at the LHC. In this paper, we calculate the direct contribution from virtual photons produced in the Drell-Yan process with an additional jet in POWHEG and find that it is significant at low invariant masses. We also simulate the background contributions from
c
c
¯
and
b
b
¯
production with POWHEG and quantify the theoretical uncertainties due to variations of the perturbative scales and parton distribution functions. We find larger relative and absolute uncertainties for the lighter
c
quarks than for heavier
b
quarks.
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