1,282 research outputs found
Random equations in aerodynamics
Literature was reviewed to identify aerodynamic models which might be treated by probablistic methods. The numerical solution of some integral equations that arise in aerodynamical problems were investigated. On the basis of the numerical studies a qualitative theory of random integral equations was developed to provide information on the behavior of the solutions of these equations (in particular, boundary and asymptotic behavior, and stability) and their statistical properties without actually obtaining explicit solutions of the equations
Well-tempered n-plet dark matter
We study simple effective models of fermionic WIMP dark matter, where the
dark matter candidate is a mixture of a Standard Model singlet and an n-plet of
SU(2) with n >= 3, stabilized by a discrete symmetry. The dark matter mass is
assumed to be around the electroweak scale, and the mixing is generated by
higher-dimensional operators, with a cutoff scale > 1 TeV. For appropriate
values of the mass parameters and the mixing we find that the observed dark
matter relic density can be generated by coannihilation. Direct detection
experiments have already excluded large parts of the parameter space, and the
next-generation experiments will further constrain these models.Comment: 25 pages, 7 figures; v2: references and plots updated, minor
corrections, conclusions unchange
Direct Chargino-Neutralino Production at the LHC: Interpreting the Exclusion Limits in the Complex MSSM
We re-assess the exclusion limits on the parameters describing the
supersymmetric (SUSY) electroweak sector of the MSSM obtained from the search
for direct chargino-neutralino production at the LHC. We start from published
limits obtained in simplified models, where for the case of heavy sleptons the
relevant branching ratio, BR(neu2->neu1 Z), is set to one. We show how the
decay mode neu2->neu1 h, which cannot be neglected in any realistic model once
kinematically allowed, substantially reduces the excluded parameter region. We
analyze the dependence of the excluded regions on the phase of the gaugino soft
SUSY-breaking mass parameter, M_1, on the mass of the light scalar tau, on tb
as well as on the squark and slepton mass scales. Large reductions in the
ranges of parameters excluded can be observed in all scenarios. The branching
ratios of charginos and neutralinos are evaluated using a full NLO calculation
for the complex MSSM. The size of the effects of the NLO calculation on the
exclusion bounds is investigated. We furthermore assess the potential reach of
the experimental analyses after collecting 100/fb at the LHC running at 13 TeV.Comment: 34 pages, 12 figures. Minor changes, matches published versio
Natural SUSY: LHC and Dark Matter direct detection experiments interplay
Natural SUSY scenarios with a low value of the parameter, are
characterised by a higgsino-like dark matter candidate, and a compressed
spectrum for the lightest higgsinos. We explore the prospects for probing this
scenario at the 13 TeV stage of the LHC via monojet searches, with various
integrated luminosity options, and demonstrate how these results are affect by
different assumptions on the achievable level of control on the experimental
systematic uncertainties. The complementarity between collider and direct
detection experiments (present and future) is also highlighted.Comment: Proceeding for the 18th International Conference From the Planck
Scale to the Electroweak Scale (Ioannina, Greece, 25-29 May 2015
Relic density of wino-like dark matter in the MSSM
The relic density of TeV-scale wino-like neutralino dark matter in the MSSM
is subject to potentially large corrections as a result of the Sommerfeld
effect. A recently developed framework enables us to calculate the
Sommerfeld-enhanced relic density in general MSSM scenarios, properly treating
mixed states and multiple co-annihilating channels as well as including
off-diagonal contributions. Using this framework, including on-shell one-loop
mass splittings and running couplings and taking into account the latest
experimental constraints, we perform a thorough study of the regions of
parameter space surrounding the well known pure-wino scenario: namely the
effect of sfermion masses being non-decoupled and of allowing non-negligible
Higgsino or bino components in the lightest neutralino. We further perform an
investigation into the effect of thermal corrections and show that these can
safely be neglected. The results reveal a number of phenomenologically
interesting but so far unexplored regions where the Sommerfeld effect is
sizeable. We find, in particular, that the relic density can agree with
experiment for dominantly wino neutralino dark matter with masses ranging from
1.7 to beyond 4 TeV. In light of these results the bounds from Indirect
Detection on wino-like dark matter should be revisited.Comment: 49 pages, 15 figure
Monojet searches for momentum-dependent dark matter interactions
We consider minimal dark matter scenarios featuring momentum-dependent couplings of the dark sector to the Standard Model. We derive constraints from existing LHC searches in the monojet channel, estimate the future LHC sensitivity for an integrated luminosity of 300 fb−1, and compare with models exhibiting conventional momentum-independent interactions with the dark sector. In addition to being well motivated by (composite) pseudo-Goldstone dark matter scenarios, momentum-dependent couplings are interesting as they weaken direct detection constraints. For a specific dark matter mass, the LHC turns out to be sensitive to smaller signal cross-sections in the momentum-dependent case, by virtue of the harder jet transverse-momentum distribution
Neutralino Decays in the Complex MSSM at One-Loop: a Comparison of On-Shell Renormalization Schemes
We evaluate two-body decay modes of neutralinos in the Minimal Supersymmetric
Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we
take into account all two-body decay channels involving charginos, neutralinos,
(scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation
of the decay widths is based on a full one-loop calculation including hard and
soft QED radiation. Of particular phenomenological interest are decays
involving the Lightest Supersymmetric Particle (LSP), i.e. the lightest
neutralino, or a neutral or charged Higgs boson. For the chargino/neutralino
sector we employ two different renormalization schemes, which differ in the
treatment of the complex phases. In the numerical analysis we concentrate on
the decay of the heaviest neutralino and show the results in the two different
schemes. The higher-order corrections of the heaviest neutralino decay widths
involving the LSP can easily reach a level of about 10-15%, while the
corrections to the decays to Higgs bosons are up to 20-30%, translating into
corrections of similar size in the respective branching ratios. The difference
between the two schemes, indicating the size of unknown two-loop corrections,
is less than order(0.1%). These corrections are important for the correct
interpretation of LSP and Higgs production at the LHC and at a future linear
e+e- collider. The results will be implemented into the Fortran code FeynHiggs.Comment: 49 pages, 27 figures, typos corrected. arXiv admin note: substantial
text overlap with arXiv:1112.0760, arXiv:1111.7289, arXiv:1204.400
Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays
According to the heavy-quark flavour symmetry, the transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays and , we perform a
phenomenological study of transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate transition form factors from
to . It is found that, although being consistent with
each other within error bars, the central values of our results for form factors at , , are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table
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