364 research outputs found
Bounds and Prospects for Stable Multiply Charged Particles at the LHC
Colored and colorless particles that are stable on collider scales and carry
exotic electric charges, so-called multiply-charged heavy stable particles
(MCHSPs), exist in extensions of the Standard Model, and can include the top
partner(s) in solutions of the hierarchy problem. To obtain bounds on
color-triplets and color-singlets of charges up to |Q|=8, we recast searches
for signatures of two production channels: the "open" channel - where the
particles are pair-produced above threshold, and are detectable in dedicated
LHC searches for stable multiply charged leptons, and the "closed" channel -
where a particle-antiparticle pair is produced as a bound state, detectable in
searches for a diphoton resonance. We recast the open lepton searches by
incorporating the relevant strong-interaction effects for color-triplets. In
both open and closed production, we provide a careful assessment of
photon-induced processes using the accurate LUXqed PDF, resulting in
substantially weaker bounds than previously claimed in the literature for the
colorless case. Our bounds for colored MCHSPs are shown for the first time, as
the LHC experiments have not searched for them directly. Generally, we obtain
nearly charge-independent lower mass limits of around 970 GeV (color-triplet
scalar), 1200 GeV (color-triplet fermion), and 880 - 900 GeV (color-singlet
fermion) from open production, and strongly charge-dependent limits from closed
production. In all cases there is a crossover between dominance by open and
closed searches at some charge. We provide prospective bounds for TeV LHC searches at integrated luminosities of 39.5 fb, 100
fb, and 300 fb. Moreover, we show that a joint observation in
the open and the closed channels allows to determine the mass, spin, color, and
electric charge of the particle
Crossover from normal to anomalous diffusion in field-aligned dipolar systems
Using molecular dynamics simulations we investigate the translational
dynamics of particles with dipolar interactions in homogenous external fields.
For a broad range of concentrations, we find that the anisotropic, yet normal
diffusive behavior characterizing weakly coupled systems becomes anomalous both
parallel and perpendicular to the field at sufficiently high dipolar coupling
and field strength. After the ballistic regime, chain formation first yields
cage-like motion in all directions, followed by transient, mixed
diffusive-superdiffusive behavior resulting from cooperative motion of the
chains. The enhanced dynamics disappears only at higher densities close to
crystallization
Non-equilibrium condensation and coarsening of field-driven dipolar colloids
In colloidal suspensions, self-organization processes can be easily fueled by
external fields. One particularly interesting class of phenomena occurs in
monolayers of dipolar particles that are driven by rotating external fields.
Here we report results from a computer simulation study of such systems
focusing on the clustering behavior also observed in recent experiments. The
key result of this paper is a novel interpretation of this pattern formation
phenomenon: We show the clustering to be a by-product of a vapor-liquid first
order phase transition. In fact, the observed dynamic coarsening process
corresponds to the spindodal demixing that occurs during such a transitionComment: 6 pages, 5 figure
The supersymmetric Higgs sector and B-Bbar mixing for large tan beta
We match the Higgs sector of the most general flavour breaking and CP
violating minimal supersymmetric standard model (MSSM) onto a generic
two-Higgs-doublet model, paying special attention to the definition of tan beta
in the effective theory. In particular no tan beta-enhanced loop corrections
appear in the relation to tan beta defined in the DRbar scheme in the MSSM. The
corrections to the Higgs-mediated flavour-changing amplitudes which result from
this matching are especially relevant for the B_d and B_s mass differences
dM_s,d for minimal flavour violation, where the superficially leading
contribution vanishes. We give a symmetry argument to explain this cancellation
and perform a systematic study of all Higgs-mediated effects, including Higgs
loops. The corrections to dM_s are at most 7% for mu>0 and M_A < 600 if
constraints from other observables are taken into account. For mu<0 they can be
larger, but are always less than about 20%. Contrary to recent claims we do not
find numerically large contributions here, nor do we find any tan beta-enhanced
contributions from loop corrections to the Higgs potential in B^+ -> tau^+ nu
or B -> X_s gamma. We further update supersymmetric loop corrections to the
Yukawa couplings, where we include all possible CP-violating phases and correct
errors in the literature. The possible presence of CP-violating phases
generated by Higgs exchange diagrams is briefly discussed as well. Finally we
provide improved values for the bag factors P^VLL_1, P^LR_2, and P^SLL_1 at the
electroweak scale.Comment: 61 page
Pattern formation of dipolar colloids in rotating fields: layering and synchronization
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We report Brownian dynamics (BD) simulation and theoretical results for a system of spherical colloidal particles with permanent dipole moments in a rotating magnetic field. Performing simulations at a fixed packing fraction and dipole coupling parameter, we construct a full non-equilibrium phase diagram as a function of the driving frequency (ω0) and field strength (B0). This diagram contains both synchronized states, where the individual particles follow the field with (on average) constant phase difference, and asynchronous states. The synchronization is accompanied by layer formation, i.e., by spatial symmetry-breaking, similar to systems of induced dipoles in rotating fields. In the permanent dipole case, however, too large ω0 yields a breakdown of layering, supplemented by complex changes of the single-particle rotational dynamics from synchronous to asynchronous behavior. We show that the limit frequencies ωc can be well described as a bifurcation in the nonlinear equation of motion of a single-particle rotating in a viscous medium. Finally, we present a simple density functional theory, which describes the emergence of layers in perfectly synchronized states as an equilibrium phase transition.DFG, GRK 1558, Kollektive Dynamik im Nichtgleichgewicht: in kondensierter Materie und biologischen Systeme
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