992 research outputs found
First-Order Electroweak Phase Transition in the Standard Model with a Low Cutoff
We study the possibility of a first-order electroweak phase transition (EWPT)
due to a dimension-six operator in the effective Higgs potential. In contrast
with previous attempts to make the EWPT strongly first-order as required by
electroweak baryogenesis, we do not rely on large one-loop thermally generated
cubic Higgs interactions. Instead, we augment the Standard Model (SM) effective
theory with a dimension-six Higgs operator. This addition enables a strong
first-order phase transition to develop even with a Higgs boson mass well above
the current direct limit of 114 GeV. The phi^6 term can be generated for
instance by strong dynamics at the TeV scale or by integrating out heavy
particles like an additional singlet scalar field. We discuss conditions to
comply with electroweak precision constraints, and point out how future
experimental measurements of the Higgs self couplings could test the idea.Comment: 5 pages, 4 figures. v2: corrected typos, improved discussion of the
case lambda<0 and added references. To be published in PR
Gravitational Waves from Warped Spacetime
We argue that the RSI model can provide a strong signature in gravitational
waves. This signal is a relic stochastic background generated during the
cosmological phase transition from an AdS-Schwarschild phase to the RS1
geometry that should occur at a temperature in the TeV range. We estimate the
amplitude of the signal in terms of the parameters of the potential stabilizing
the radion and show that over much of the parameter region in which the phase
transition completes, a signal should be detectable at the planned space
interferometer, LISA.Comment: 18 pages, 15 figures; v2: discussion improved, in particular on the
justification of the thick wall approximation. 6 figures added. 4 pi factor
corrected in perturbativity bound. N-dependence displayed. Conclusions
unchanged. JHEP versio
Millau viaduct geotechnical studies and foundations
AbstractThe Millau viaduct over the Tarn River is an exceptional bridge considering the height under the deck and the 2.5km total length. Each of the seven high piers is founded on a thick raft setting on four large piles of 5m in diameter and 10–15m deep. The ground schematically consists of limestone in the north and of marls in the south. As the bridge is very sensitive to foundation settlements, the concessionary company decided to use the observational method for controlling the displacements and if necessary stabilize the foundations. The measurements show that the movements have remained small and admissible, particularly in terms of the rotations. The settlements have not occurred continuously under the load, but by steps
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
Investigating Problem-Based Learning Tutorship in Medical and Engineering Programs in Malaysia
Although Malaysia was the first country in Asia to adopt problem-based learning (PBL), the impact that this has had on its tutors remains largely unexplored. This paper details a qualitative study of the changing perceptions of teaching roles in two groups of problem-based learning tutors in two institutional contexts—one in medicine located in Kuala Lumpur and one in engineering located in Johor Bahru. Using Interpretive Phenomenological Analysis, the authors attempt to describe the way in which the two groups have experienced their changing professional world, and the mental processes through which they rationalize the transformation of Malaysia’s educational landscape. This paper discusses four themes of analysis: (1) Tutor perceptions are embedded in the context of Malaysian hierarchical social structures, (2) tutors recount a rewarding but challenging move to PBL, (3) tutors display widely different attitudes towards the role of expertise in PBL, and (4) tutors attempt to construct explanations and rationalize their emotional experiences with PBL
Vegetation response to the "African Humid Period" termination in Central Cameroon (7° N) – new pollen insight from Lake Mbalang
A new pollen sequence from the Lake Mbalang (7°19´ N, 13°44´ E, 1110 m a.s.l.) located on the eastern Adamawa plateau, in Central Cameroon, is presented in this paper to analyze the Holocene African Humid Period (AHP) termination and related vegetation changes at 7° N in tropical Africa, completing an important transect for exploring shifts in the northern margin of the African Monsoon. This sequence, spanning the last 7000 cal yr BP, shows that the vegetation response to this transitional climatic period was marked by significant successional changes within the broad context of long-term aridification. Semi-deciduous/sub-montane forest retreat in this area is initially registered as early as ca. 6100 cal yr BP and modern savannah was definitely established at ca. 3000 cal yr BP and stabilized at ca. 2400 cal yr BP; but a slight forest regeneration episode is observed between ca. 5200 and ca. 4200 cal yr BP. In this area with modern high rainfall, increasing in the length of the dry season during the AHP termination linked to a contraction of the northern margin of the Intertropical Convergence Zone (ITCZ) from ca. 6100 cal yr BP onward, probably associated with decreasing in cloud cover and/or fog frequency, has primarily controlled vegetation dynamics and above all the disappearance of the forested environment on the Adamawa plateau. Compared to previous studies undertaken in northern tropical and Central Africa, this work clearly shows that the response of vegetation to transitional periods between climatic extremes such as the AHP termination might be different in timing, mode and amplitude according to the regional climate of the study sites, but also according to the stability of vegetation before and during these climatic transitions
Dirac Neutrino Dark Matter
We investigate the possibility that dark matter is made of heavy Dirac
neutrinos with mass in the range [O(1) GeV- a few TeV] and with suppressed but
non-zero coupling to the Standard Model Z as well as a coupling to an
additional Z' gauge boson. The first part of this paper provides a
model-independent analysis for the relic density and direct detection in terms
of four main parameters: the mass, the couplings to the Z, to the Z' and to the
Higgs. These WIMP candidates arise naturally as Kaluza-Klein states in
extra-dimensional models with extended electroweak gauge group SU(2)_L* SU(2)_R
* U(1). They can be stable because of Kaluza-Klein parity or of other discrete
symmetries related to baryon number for instance, or even, in the low mass and
low coupling limits, just because of a phase-space-suppressed decay width. An
interesting aspect of warped models is that the extra Z' typically couples only
to the third generation, thus avoiding the usual experimental constraints. In
the second part of the paper, we illustrate the situation in details in a
warped GUT model.Comment: 35 pages, 25 figures; v2: JCAP version; presentation and plots
improved, results unchange
Observation of vortex coalescence in the anisotropic spin-triplet superconductor SrRuO
We present direct imaging of magnetic flux structures in the anisotropic,
spin-triplet superconductor SrRuO using a scanning SQUID
microscope. Individual quantized vortices were seen at low magnetic fields.
Coalescing vortices forming flux domains were revealed at intermediate fields.
Based on our observations we suggest that a mechanism intrinsic to the material
stabilizes the flux domains against the repulsive vortex-vortex interaction.
Topological defects like domain walls can provide this, implying proof for
unconventional chiral superconductivity.Comment: submitted to PR
- …