104 research outputs found
Multi-lepton signatures at LHC from sneutrino dark matter
We investigate multi-lepton LHC signals arising from an extension at the
grand unification scale of the standard minimal supersymmetric model (MSSM)
involving right-handed neutrino superfields. In this framework neutrinos have
Dirac masses and the mixed sneutrinos are the lightest supersymmetric particles
and hence the dark matter candidates. We analyze the model parameter space in
which the sneutrino is a good dark matter particle and has a direct detection
cross-section compatible with the LUX bound. Studying the supersymmetric mass
spectrum of this region, we find several signatures relevant for LHC, which are
distinct from the predictions of the MSSM with neutralino dark matter. For
instance two opposite sign and different flavor leptons, three uncorrelated
leptons and long-lived staus are the most representative. Simulating both the
signal and expected background, we find that the multi-lepton signatures and
the long-lived stau are in the reach of the future run of LHC with a luminosity
of 100/fb. We point out that if one of these signatures is detected, it might
be an indication of sneutrino dark matter.Comment: 34 pages, 14 figures and 6 tables; this version matches the published
on
New techniques for chargino-neutralino detection at LHC
The recent LHC discovery of a Higgs-like boson at 126 GeV has important
consequences for SUSY, pushing the spectrum of strong-interacting
supersymmetric particles to high energies, very difficult to probe at the LHC.
This gives extra motivation to study the direct production of electroweak
particles, as charginos and neutralinos, which are presently very poorly
constrained. The aim of this work is to improve the analysis of
chargino-neutralino pair production at LHC, focusing on the kinematics of the
processes. We propose a new method based on the study of the poles of a certain
kinematical variable. This complements other approaches, giving new information
about the spectrum and improving the signal-to-background ratio. We illustrate
the method in particular SUSY models, and show that working with the LHC at
100/fb luminosity one would be able to distinguish the SUSY signal from the
Standard Model background.Comment: accepted for publication in JHE
Dark matter protohalos in MSSM-9 and implications for direct and indirect detection
We study how the kinetic decoupling of dark matter (DM) within a minimal
supersymmetric extension of the standard model, by adopting nine independent
parameters (MSSM-9), could improve our knowledge of the properties of the DM
protohalos. We show that the most probable neutralino mass regions, which
satisfy the relic density and the Higgs mass contraints, are those with the
lightest supersymmetric neutralino mass around 1 TeV and 3 TeV, corresponding
to Higgsino-like and Wino-like neutralino, respectively. The kinetic decoupling
temperature in the MSSM-9 scenario leads to a most probable protohalo mass in a
range of . The part of the
region closer to 2 TeV gives also important contributions from the
neutralino-stau co-annihilation, reducing the effective annihilation rate in
the early Universe. We also study how the size of the smallest DM substructures
correlates to experimental signatures, such as the spin-dependent and
spin-independent scattering cross sections, relevant for direct detection of
DM. Improvements on the spin-independent sensitivity might reduce the most
probable range of the protohalo mass between 10 and
10, while the expected spin-dependent sensitivity
provides weaker constraints. We show how the boost of the luminosity due to DM
annihilation increases, depending on the protohalo mass. In the Higgsino case,
the protohalo mass is lower than the canonical value often used in the
literature (10), while does not
deviate from cm s; there is no
significant enhancement of the luminosity. On the contrary, in the Wino case,
the protohalo mass is even lighter, and is two orders
of magnitude larger; as its consequence, we see a substantial enhancement of
the luminosity.Comment: 26 pages, 8 figure
MSSM Forecast for the LHC
We perform a forecast of the MSSM with universal soft terms (CMSSM) for the
LHC, based on an improved Bayesian analysis. We do not incorporate ad hoc
measures of the fine-tuning to penalize unnatural possibilities: such
penalization arises from the Bayesian analysis itself when the experimental
value of is considered. This allows to scan the whole parameter space,
allowing arbitrarily large soft terms. Still the low-energy region is
statistically favoured (even before including dark matter or g-2 constraints).
Contrary to other studies, the results are almost unaffected by changing the
upper limits taken for the soft terms. The results are also remarkable stable
when using flat or logarithmic priors, a fact that arises from the larger
statistical weight of the low-energy region in both cases. Then we incorporate
all the important experimental constrains to the analysis, obtaining a map of
the probability density of the MSSM parameter space, i.e. the forecast of the
MSSM. Since not all the experimental information is equally robust, we perform
separate analyses depending on the group of observables used. When only the
most robust ones are used, the favoured region of the parameter space contains
a significant portion outside the LHC reach. This effect gets reinforced if the
Higgs mass is not close to its present experimental limit and persits when dark
matter constraints are included. Only when the g-2 constraint (based on
data) is considered, the preferred region (for ) is well inside
the LHC scope. We also perform a Bayesian comparison of the positive- and
negative- possibilities.Comment: 42 pages: added figures and reference
Indirect and direct detection prospect for TeV dark matter in the MSSM-9
We investigate the prospects of indirect and direct dark matter searches
within the minimal supersymmetric standard model with nine parameters (MSSM-9).
These nine parameters include three gaugino masses, Higgs, slepton and squark
masses, all treated independently. We perform a Bayesian Monte Carlo scan of
the parameter space taking into consideration all available particle physics
constraints such as the Higgs mass of 126 GeV, upper limits on the scattering
cross-section from direct-detection experiments, and assuming that the MSSM-9
provides all the dark matter abundance through thermal freeze-out mechanism.
Within this framework we find two most probable regions for dark matter: 1-TeV
higgsino-like and 3-TeV wino-like neutralinos. We discuss prospects for future
indirect (in particular the Cherenkov Telescope Array, CTA) and direct
detection experiments. We find that for slightly contracted dark matter
profiles in our Galaxy, which can be caused by the effects of baryonic infall
in the Galactic center, CTA will be able to probe a large fraction of the
remaining allowed region in synergy with future direct detection experiments
like XENON-1T.Comment: 8 pages, 3 figure
The health of SUSY after the Higgs discovery and the XENON100 data
We analyze the implications for the status and prospects of supersymmetry of
the Higgs discovery and the last XENON data. We focus mainly, but not only, on
the CMSSM and NUHM models. Using a Bayesian approach we determine the
distribution of probability in the parameter space of these scenarios. This
shows that, most probably, they are now beyond the LHC reach . This negative
chances increase further (at more than 95% c.l.) if one includes dark matter
constraints in the analysis, in particular the last XENON100 data. However, the
models would be probed completely by XENON1T. The mass of the LSP neutralino
gets essentially fixed around 1 TeV. We do not incorporate ad hoc measures of
the fine-tuning to penalize unnatural possibilities: such penalization arises
automatically from the careful Bayesian analysis itself, and allows to scan the
whole parameter space. In this way, we can explain and resolve the apparent
discrepancies between the previous results in the literature. Although SUSY has
become hard to detect at LHC, this does not necessarily mean that is very
fine-tuned. We use Bayesian techniques to show the experimental Higgs mass is
at off the CMSSM or NUHM expectation. This is substantial but
not dramatic. Although the CMSSM or the NUHM are unlikely to show up at the
LHC, they are still interesting and plausible models after the Higgs
observation; and, if they are true, the chances of discovering them in future
dark matter experiments are quite high
LHC and dark matter phenomenology of the NUGHM
We present a Bayesian analysis of the NUGHM, a supersymmetric scenario with
non-universal gaugino masses and Higgs masses, including all the relevant
experimental observables and dark matter constraints. The main merit of the
NUGHM is that it essentially includes all the possibilities for dark matter
(DM) candidates within the MSSM, since the neutralino and chargino spectrum
-and composition- are as free as they can be in the general MSSM. We identify
the most probable regions in the NUHGM parameter space, and study the
associated phenomenology at the LHC and the prospects for DM direct detection.
Requiring that the neutralino makes all of the DM in the Universe, we identify
two preferred regions around ,
which correspond to the (almost) pure Higgsino and wino case. There exist other
marginal regions (e.g. Higgs-funnel), but with much less statistical weight.
The prospects for detection at the LHC in this case are quite pessimistic, but
future direct detection experiments like LUX and XENON1T, will be able to probe
this scenario. In contrast, when allowing other DM components, the prospects
for detection at the LHC become more encouraging -- the most promising signals
being, beside the production of gluinos and squarks, the production of the
heavier chargino and neutralino states, which lead to WZ and same-sign WW final
states -- and direct detection remains a complementary, and even more powerful,
way to probe the scenario.Comment: The Sommerfeld enhancement has been included in the computation of
the relic density and in the discussion of indirect-detection limits. Some
references have been adde
Constraints on sneutrino dark matter from LHC Run 1
A mostly right-handed sneutrino as the lightest supersymmetric particle (LSP)
is an interesting dark matter candidate, leading to LHC signatures which can be
quite distinct from those of the conventional neutralino LSP. Using
SModelSv1.0.1 for testing the model against the limits published by ATLAS and
CMS in the context of so-called Simplified Model Spectra (SMS), we investigate
to what extent the supersymmetry searches at Run 1 of the LHC constrain the
sneutrino-LSP scenario. Moreover, we discuss the most relevant topologies for
which no SMS results are provided by the experimental collaborations but which
would allow to put more stringent constraints on sneutrino LSPs. These include,
for instance, the mono-lepton signature which should be particularly
interesting to consider at Run 2 of the LHC.Comment: 30 pages, 23 figures, matches published versio
Quantifying the tension between the Higgs mass and (g-2)_mu in the CMSSM
Supersymmetry has been often invoqued as the new physics that might reconcile
the experimental muon magnetic anomaly, a_mu, with the theoretical prediction
(basing the computation of the hadronic contribution on e^+ e^- data). However,
in the context of the CMSSM, the required supersymmetric contributions (which
grow with decreasing supersymmetric masses) are in potential tension with a
possibly large Higgs mass (which requires large stop masses). In the limit of
very large m_h supersymmetry gets decoupled, and the CMSSM must show the same
discrepancy as the SM with a_mu . But it is much less clear for which size of
m_h does the tension start to be unbearable. In this paper, we quantify this
tension with the help of Bayesian techniques. We find that for m_h > 125 GeV
the maximum level of discrepancy given current data (~ 3.3 sigma) is already
achieved. Requiring less than 3 sigma discrepancy, implies m_h < 120 GeV. For a
larger Higgs mass we should give up either the CMSSM model or the computation
of a_mu based on e^+ e^-; or accept living with such inconsistency
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