3,657 research outputs found
The Distribution of Path Losses for Uniformly Distributed Nodes in a Circle
When simulating a wireless network, users/nodes are usually assumed to be distributed uniformly in space. Path losses between nodes in a simulated network are generally calculated by determining the distance between every pair of nodes and applying a suitable path loss model as a function of this distance (power of distance with an environment-specific path loss exponent) and adding a random component to represent the log-normal shadowing. A network with nodes consists of (−1)/2 path loss values. In order to generate statistically significant results for system-level simulations, Monte Carlo simulations must be performed where the nodes are randomly distributed at the start of every run. This is a time-consuming operation which need not be carried out if the distribution of path losses between the nodes is known. The probability density function (pdf) of the path loss between the centre of a circle and a node distributed uniformly within a the circle is derived in this work
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
En-gauging Naturalness
The discovery of a 125.5 GeV Higgs with standard model-like couplings and
naturalness considerations motivate gauge extensions of the MSSM. We analyse
two variants of such an extension and carry out a phenomenological study of
regions of the parameter space satisfying current direct and indirect
constraints, employing state-of-the art two-loop RGE evolution and GMSB
boundary conditions. We find that due to the appearance of non-decoupled
D-terms it is possible to obtain a 125.5 GeV Higgs with stops below 2 TeV,
while the uncolored sparticles could still lie within reach of the LHC. We
compare the contributions of the stop sector and the non-decoupled D-terms to
the Higgs mass, and study their effect on the Higgs couplings. We further
investigate the nature of the next-to lightest supersymmetric particle, in
light of the GMSB motivated searches currently being pursued by ATLAS and CMS.Comment: 45 pages, 17 figures, Supplementary material
SupplementaryQSMxEW-Regime1.pdf attached in source. v2: preprint number added
v3: Appendix A.6, Published in EPJ
Threshold enhancement of diphoton resonances
The data collected by the LHC collaborations at an energy of 13 TeV indicates
the presence of an excess in the diphoton spectrum that would correspond to a
resonance of a 750 GeV mass. The apparently large production cross section is
nevertheless very difficult to explain in minimal models. We consider the
possibility that the resonance is a pseudoscalar boson with a two--photon
decay mediated by a charged and uncolored fermion having a mass at the threshold and a very small decay width, MeV; one can then generate
a large enhancement of the amplitude which explains the excess
without invoking a large multiplicity of particles propagating in the loop,
large electric charges and/or very strong Yukawa couplings. The implications of
such a threshold enhancement are discussed in two explicit scenarios: i) the
Minimal Supersymmetric Standard Model in which the state is produced via
the top quark mediated gluon fusion process and decays into photons
predominantly through loops of charginos with masses close to and
ii) a two Higgs doublet model in which is again produced by gluon fusion
but decays into photons through loops of vector--like charged heavy leptons. We
also comment on a minimal scenario in which the state couples only to
photons through a heavy lepton loop and is both produced and decays through
this coupling. In all these scenarios, while the mass of the charged fermion
has to be adjusted to be extremely close to half of the resonance mass, the
small total widths are naturally obtained if only suppressed three-body decay
channels occur. Finally, the implications of some of these scenarios for dark
matter are discussed.Comment: 15 pages, 4 figures, version submitted to journal with typos
correcte
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
- …