256 research outputs found
Boundary Zonal Flow in Rotating Turbulent Rayleigh-BĂ©nard Convection
For rapidly rotating turbulent RayleighâBĂ©nard convection in a slender cylindrical cell, experiments and direct numerical simulations reveal a boundary zonal flow (BZF) that replaces the classical large-scale circulation. The BZF is located near the vertical side wall and enables enhanced heat transport there. Although the azimuthal velocity of the BZF is cyclonic (in the rotating frame), the temperature is an anticyclonic traveling wave of mode one, whose signature is a bimodal temperature distribution near the radial boundary. The BZF width is found to scale like Ra1/4Ek2/3 where the Ekman number Ek decreases with increasing rotation rate
Minimal Z' models: present bounds and early LHC reach
We consider `minimal' Z' models, whose phenomenology is controlled by only
three parameters beyond the Standard Model ones: the Z' mass and two effective
coupling constants. They encompass many popular models motivated by grand
unification, as well as many arising in other theoretical contexts. This
parameterization takes also into account both mass and kinetic mixing effects,
which we show to be sizable in some cases. After discussing the interplay
between the bounds from electroweak precision tests and recent direct searches
at the Tevatron, we extend our analysis to estimate the early LHC discovery
potential. We consider a center-of-mass energy from 7 towards 10 TeV and an
integrated luminosity from 50 to several hundred pb^-1, taking all existing
bounds into account. We find that the LHC will start exploring virgin land in
parameter space for M_Z' around 700 GeV, with lower masses still excluded by
the Tevatron and higher masses still excluded by electroweak precision tests.
Increasing the energy up to 10 TeV, the LHC will start probing a wider range of
Z' masses and couplings, although several hundred pb^-1 will be needed to
explore the regions of couplings favored by grand unification and to overcome
the Tevatron bounds in the mass region around 250 GeV.Comment: 25 pages. v2: small improvements and minor corrections, version
accepted for publication on JHE
Brane-induced supersymmetry breaking
We study spontaneous supersymmetry breaking induced by brane-localized
dynamics in five-dimensional supergravity compactified on S^1/Z_2. We consider
a model with gravity in the bulk and matter localized on tensionless branes at
the orbifold fixed points. We assume that the brane dynamics give rise to
effective brane superpotentials that trigger the supersymmetry breaking. We
analyze in detail the super-Higgs effect. We compute the full spectrum and show
that the symmetry breaking is spontaneous but nonlocal in the fifth dimension.
We demonstrate that the model can be interpreted as a new, non-trivial
implementation of a coordinate-dependent Scherk-Schwarz compactification.Comment: 15 pages. v2: improved treatment of brane actions, relation with
conventional Scherk-Schwarz mechanism clarified, version to be published in
JHE
On the two-loop sbottom corrections to the neutral Higgs boson masses in the MSSM
We compute the O(ab*as) two-loop corrections to the neutral Higgs boson
masses in the Minimal Supersymmetric Standard Model, using the effective
potential approach. Such corrections can be important in the region of
parameter space corresponding to tan(beta)>>1 and sizeable mu. In spite of the
formal analogy with the O(at*as) corrections, there are important differences,
since the dominant effects are controlled by the sbottom-Higgs scalar
couplings. We propose a convenient renormalization scheme that avoids
unphysically large threshold effects associated with the bottom mass, and
absorbs the bulk of the O(ab*as + ab*at) corrections into the one-loop
expression. We give general explicit formulae for the O(ab*as) corrections to
the neutral Higgs boson mass matrix. We also discuss the importance of the
O(ab^2) corrections and derive a formula for their contribution to mh in a
simple limiting case.Comment: 14 pages, 4 figures. Version to appear in Nucl. Phys.
On general flux backgrounds with localized sources
We derive new consistency conditions for string compactifications with
generic fluxes (RR, NSNS, geometrical) and localized sources (D-branes,
NS-branes, KK-monopoles). The constraints are all related by string dualities
and share a common origin in M-theory. We also find new sources of
instabilities. We discuss the importance of these conditions for the
consistency of the effective action and for the study of interpolating
solutions between vacua.Comment: 29 pages, 2 figures, v2: published versio
B-physics constraints on baryon number violating couplings: grand unification or R-parity violation
We investigate the role that baryon number violating interactions may play in
phenomenology. Present in various grand unified theories, supersymmetric
theories with R-parity violation and composite models, a diquark state could be
quite light. Using the data on B decays as well as mixing, we
find strong constraints on the couplings that such a light diquark state may
have with the Standard Model quarks.Comment: 19 pages, latex, no figures, 13 tables include
Constraints on Baryon-Nonconserving Yukawa Couplings in a Supersymmetric Theory
The 1-loop evolution of couplings in the minimal supersymmetric standard
model, extended to include baryon nonconserving operators through
explicit -parity violation, is considered keeping only
superpotential terms involving the maximum possible number of third generation
superfields. If all retained Yukawa couplings are required to remain in
the perturbative domain upto the scale of gauge group unification,
upper bounds ensue on the magnitudes of the coupling strengths at
the supersymmetry breaking scale, independent of the model of unification. They
turn out to be similar to the corresponding fixed point values reached from a
wide range of (including all greater than unity) at the unification
scale. The coupled evolution of the top and Yukawa couplings results
in a reduction of the fixed point value of the former.Comment: PRL-TH-94/8 and TIFR/TH/94-7, 15 pages, LaTe
Resource recovery and low carbon transitions: The hidden impacts of substituting cement with imported âwasteâ materials from coal and steel production
Here we investigate the increasingly complex relationship between the resource recovery practices of the UK concrete industryandongoing low-carbontransitions takingplaceinelectricityandsteel.ReductionsinUKcoalbased electricity and primary steel production are reducing domestic availability of residues â coal ash and steel slag â that are used to replace cement in concrete; for decarbonisation purposes and to increase concrete quality. This is leading to an unusual mass-transportation of âwastesâ from the Global South to Global North. Focusing closely upon the mitigation pathways of concrete producers, we develop an inter-industry model of material ïŹows, and a diversity of scenarios and sensitivity tests, to consider how resource recovery practices and carbon emissions of the three sectors may evolve. A continuation of domestic shortages in waste-derived cement substitutes appears inevitable and future international shortages possible. But even if foreign producers supplied enough cement substitutes to meet UK demand, the broader carbon implications of such trade may be far from benign. Using a revenue-based approach to allocate emissions to coal ash leads to a wide range of embodied carbon estimates â from relatively low (0.15t.CO2/t.ash) to exceeding that of traditional Portland cement (1t.CO2/t.ash). However, the carbonassociated withinternationally traded recovered resources currently stands behindaâdouble-blindâsystemofaccounting: emissionsdonotregisterintheconventionalterritorialaccountsof theimportingcountry andtheymaybehiddenfromitsconsumption-based accountsaswell.Theimpactsofsuch trade and related carbon accounting conventions are unclear and we emphasise the need for further investigation. To this end, our results demonstrate the importance of incorporating highly interconnected sectors and international trade into analyses of low-carbon transitions, and highlight the challenges this presents for designing appropriate policies, accounting frameworks, and interdisciplinary impact assessment methods that look beyond sectorial and national horizons.The UK Natural Environment Research Council (NERC), UK Economic and Social Research Council (ESRC) and Department for Environment, Food & Rural AïŹairs (DEFRA
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