Why the Water Bridge does not collapse

In 2007 an interesting phenomenon was discovered: a thread of water, the so-called water bridge (WB), can hang between two glass beakers filled with deionized water if voltage is applied to them. We analyze the available explanations of the WB stability and propose a completely different one: the force that supports the WB is the surface tension of water and the role of electric field is not to allow the WB to reduce its surface energy by means of breaking into separate drops.Comment: 4 pages, 3 figure

Quark-antiquark pair production in space-time dependent fields

Fermion-antifermion pair-production in the presence of classical fields is described based on the retarded and advanced fermion propagators. They are obtained by solving the equation of motion for the Dirac Green's functions with the respective boundary conditions to all orders in the field. Subsequently, various approximation schemes fit for different field configurations are explained. This includes longitudinally boost-invariant forms. Those occur frequently in the description of ultrarelativistic heavy-ion collisions in the semiclassical limit. As a next step, the gauge invariance of the expression for the expectation value of the number of produced fermion-antifermion pairs as a functional of said propagators is investigated in detail. Finally, the calculations are carried out for a longitudinally boost-invariant model-field, taking care of the last issue, especially.Comment: 32 pages, 8 figures, revised versio

Behaviour change at work: Empowering energy efficiency in the workplace through user-centred design

Copyright @ 2011 University of California eScholarship RepositoryCO2 emissions from non-domestic buildings - primarily workplaces - make up 18 percent of the UK's carbon footprint. A combination of technology advances and behavioural changes have the potential to make significant impact, but interventions have often been planned in ways which do not take into account the needs, levels of understanding and everyday behavioural contexts of building users - and hence do not achieve the hoped-for success.This paper provides a brief introduction to the Empower project, a current industrial-academic collaboration in the UK which is applying methods from user-centred design practice to understand diverse users' needs, priorities, mental models of energy and decision-making heuristics - as well as the affordances available to them - in a number of office buildings. We are developing and trialling a set of low-cost, simple software interventions tailored to multiple user groups with different degrees of agency over their energy use, which seek to influence more energy efficient behaviour at work in areas such as HVAC, lighting and equipment use. The project comprises an ethnographic research phase, a participatory design programme involving building users in the design of interventions, and iterative trials in a large office building in central London

Late Reheating, Hadronic Jets and Baryogenesis

If inflaton couples very weakly to ordinary matter the reheating temperature of the universe can be lower than the electroweak scale. In this letter we show that the late reheating occurs in a highly non-uniform way, within narrow areas along the jets produced by ordinary particles originated from inflaton decays. Depending on inflaton mass and decay constant, the initial temperature inside the lumps of the overheated plasma may be large enough to trigger the unsuppressed sphaleron processes with baryon number non-conservation, allowing for efficient local electroweak baryogenesis.Comment: 4 pages, 2 figures, revtex

Higgs Boson Exempt No-Scale Supersymmetry and its Collider and Cosmology Implications

One of the most straightforward ways to address the flavor problem of low-energy supersymmetry is to arrange for the scalar soft terms to vanish simultaneously at a scale $M_{c}$ much larger than the electroweak scale. This occurs naturally in a number of scenarios, such as no-scale models, gaugino mediation, and several models with strong conformal dynamics. Unfortunately, the most basic version of this approach that incorporates gaugino mass unification and zero scalar masses at the grand unification scale is not compatible with collider and dark matter constraints. However, experimental constraints can be satisfied if we exempt the Higgs bosons from flowing to zero mass value at the high scale. We survey the theoretical constructions that allow this, and investigate the collider and dark matter consequences. A generic feature is that the sleptons are relatively light. Because of this, these models frequently give a significant contribution to the anomalous magnetic moment of the muon, and neutralino-slepton coannihilation can play an important role in obtaining an acceptable dark matter relic density. Furthermore, the light sleptons give rise to a large multiplicity of lepton events at colliders, including a potentially suggestive clean trilepton signal at the Tevatron, and a substantial four lepton signature at the LHC.Comment: 36 pages, 16 figure

The Minimal Model for Dark Matter and Unification

Gauge coupling unification and the success of TeV-scale weakly interacting dark matter are usually taken as evidence of low energy supersymmetry (SUSY). However, if we assume that the tuning of the higgs can be explained in some unnatural way, from environmental considerations for example, SUSY is no longer a necessary component of any Beyond the Standard Model theory. In this paper we study the minimal model with a dark matter candidate and gauge coupling unification. This consists of the SM plus fermions with the quantum numbers of SUSY higgsinos, and a singlet. It predicts thermal dark matter with a mass that can range from 100 GeV to around 2 TeV and generically gives rise to an electric dipole moment that is just beyond current experimental limits, with a large portion of its allowed parameter space accessible to next generation EDM and direct detection experiments. We study precision unification in this model by embedding it in a 5-D orbifold GUT where certain large threshold corrections are calculable, achieving gauge coupling and b-tau unification, and predicting a rate of proton decay just beyond current limits.Comment: 20 pages, 10 figures. v2: Minor typos and Reference errors corrected. Modified explanation of the KK mode contribution to runnin

Modeling sand slides by a mechanics-based degenerate parabolic equation

Avalanching plays a crucial role in granular materials dynamics, in particular in the evolution of the shape of the leeward side of sand dunes. This paper presents a physically-based mathematical model capable of reproducing the kinematic evolution of the surface of sand piles and to obtain eventually the stationary configurations, in the presence of external sources as well. Simulation results with different boundary conditions and geometries are reported in order to show the high flexibility of the model. The model is also validated by means of comparison with the experimental results of different authors

Unstable Heavy Majorana Neutrinos and Leptogenesis

We propose a new mechanism producing a non-vanishing lepton number asymmetry, based on decays of heavy Majorana neutrinos. If they are produced out of equilibrium, as occurs in preheating scenario, and are superpositions of mass eigenstates rapidly decaying, their decay rates contains interference terms provided the mass differences $\Delta m$ are small compared to widths $\Gamma$. The resulting lepton asymmetry, which is the analogue of the time-integrated CP asymmetry in $B^0-\bar{B}^0$ system, is found to be proportional to $\Delta m/\Gamma$.Comment: 18 pages, latex, revised version to be published in Phys. Rev.

Reheating Temperature and Inflaton Mass Bounds from Thermalization After Inflation

We consider the conditions for the decay products of perturbative inflaton decay to thermalize. The importance of considering the full spectrum of inflaton decay products in the thermalization process is emphasized. It is shown that the delay between the end of inflaton decay and thermalization allows the thermal gravitino upper bound on the reheating temperature to be raised from 10^{8} GeV to as much as 10^{12} GeV in realistic inflation models. Requiring that thermalization occurs before nucleosynthesis imposes an upper bound on the inflaton mass as a function of the reheating temperature, m_{S} < 10^{10} (T_{R}/1 GeV)^{7/9} GeV. It is also shown that even in realistic inflation models with relatively large reheating temperatures, it is non-trivial to have thermalization before the electroweak phase transition temperature. Therefore the thermal history of the Universe is very sensitive to details of the inflation model.Comment: 12 Pages LaTeX. Catalysed thermalization discussion correcte

Thermalization After Inflation and Reheating Temperature

We present a detailed examination of thermalization after inflation for perturbative inflaton decay. Different interactions among particles in the plasma of inflaton decay products are considered and it will be shown that 2 -> 2 scatterings and particle decay are the important ones. We show that thermalization occurs after decays dominate scatterings, and that depending on the typical mass scale of inflaton decay products, different situations may arise. In particular, thermalization may be delayed until late times, in which case the bounds from thermal gravitino production on supersymmetric models of inflation are considerably relaxed. We will also consider the case where the observable sector consists only of the MSSM matter content, and point out that flat directions with large vevs may result in earlier thermalization of the plasma and push the reheat temperature towards its upper limit.Comment: 18 pages, LaTeX, a few references added and revise