3,521 research outputs found
Status Report on Universal Extra Dimensions After LHC8
Although they do not address the hierarchy problem, models with Universal
Extra Dimensions have attracted a lot of attention as simple benchmark models
characterized by small mass splittings and a dark matter WIMP played by the
Lightest Kaluza-Klein particle (LKP). We review their status, with emphasis on
the minimal implementation in 5 dimensions (MUED) in which the LKP is a massive
hypercharge gauge boson. In this case, the mass range accounting for the
correct dark matter abundance (around 1.4 TeV) remains untouched by LHC8 and is
out of reach of present DM direct detection experiments. However, LHC14 can
probe the relevant region in the 3-lepton channel.Comment: Invited review for special issue on "Extra dimensions vs Collider
Physics" to appear in IJMPA. 14 pages, 9 figures; v2: Figure 5 clarified and
references added; v3:comment added on low cutoff cas
Higgsogenesis
In addition to explaining the masses of elementary particles, the Higgs boson
may have far-reaching implications for the generation of the matter content in
the Universe. For instance, the Higgs plays a key role in two main theories of
baryogenesis, namely electroweak baryogenesis and leptogenesis. In this letter,
we propose a new cosmological scenario where the Higgs chemical potential
mediates asymmetries between visible and dark matter sectors, either generating
a baryon asymmetry from a dark matter asymmetry or vice-versa. We illustrate
this mechanism with a simple model with two new fermions coupled to the Higgs
and discuss associated signatures.Comment: 5 pages, 2 figures; v2: Intro and conclusion improved, clarifications
added, results unchanged. Compared to the PRL version, this arxiv version
contains two extra plots, one additional table and a slightly longer
conclusio
Gravitational Waves from Phase Transitions at the Electroweak Scale and Beyond
If there was a first order phase transition in the early universe, there
should be an associated stochastic background of gravitational waves. In this
paper, we point out that the characteristic frequency of the spectrum due to
phase transitions which took place in the temperature range 100 GeV - 10^7 GeV
is precisely in the window that will be probed by the second generation of
space-based interferometers such as the Big Bang Observer (BBO). Taking into
account the astrophysical foreground, we determine the type of phase
transitions which could be detected either at LISA, LIGO or BBO, in terms of
the amount of supercooling and the duration of the phase transition that are
needed. Those two quantities can be calculated for any given effective scalar
potential describing the phase transition. In particular, the new models of
electroweak symmetry breaking which have been proposed in the last few years
typically have a different Higgs potential from the Standard Model. They could
lead to a gravitational wave signature in the milli-Hertz frequency, which is
precisely the peak sensitivity of LISA. We also show that the signal coming
from phase transitions taking place at T ~ 1-100 TeV could entirely screen the
relic gravitational wave signal expected from standard inflationary models.Comment: 18 pages, 24 figure
QCD-induced Electroweak Phase Transition
Phase transitions associated with nearly conformal dynamics are known to lead
to significant supercooling. A notorious example is the phase transition in
Randall-Sundrum models or their CFT duals. In fact, it was found that the phase
transition in this case is first-order and the tunneling probability for the
radion/dilaton is so small that the system typically remains trapped in the
false vacuum and the phase transition never completes. The universe then keeps
expanding and cooling. Eventually the temperature drops below the QCD scale. We
show that the QCD condensates which subsequently form give an additional
contribution to the radion/dilaton potential, an effect which had been ignored
so far. This significantly reduces the barrier in the potential and allows the
phase transition to complete in a substantially larger region of parameter
space. Due to the supercooling, electroweak symmetry is then broken
simultaneously. This class of models therefore naturally leads to an
electroweak phase transition taking place at or below QCD temperatures, with
interesting cosmological implications and signatures.Comment: 33 pages, 5 figure
Particle Identification for Physics beyond the LHC
Accelerator physics beyond the LHC is expected to provide precision in the
study of new physics processes which the LHC may have already unveiled and to
extend the high energy frontier beyond its reach, in the multi-TeV domain. In
this paper I review the anticipated needs in terms of particle identification
of this physics program in relation to the experimental conditions.Comment: 6 pages, 4 figures, invited contribution to the Second Workshop on
advanced Transition Radiation Detectors for accelerators and space
applications, Bari, September 200
Payment periods in 2009 - one year on from the economic modernisation act.
Payemnt periods shortened in 2009. The decline is no longer due entirely to SMEs; it now concerns MTEs a well as large companies. It generates cash earnings, chiefly for SMEs.activity, profitability, debt, investment, SMEs, MTEs.
Supergravity Inspired Warped Compactifications and Effective Cosmological Constants
We propose a supergravity inspired derivation of a Randall-Sundrum's type
action as an effective description of the dynamics of a brane coupled to the
bulk through gravity only. The cosmological constants in the bulk and on the
brane appear at the classical level when solving the equations of motion
describing the bosonic sector of supergravities in ten and eleven dimensions
coupled to the brane. They are related to physical quantities like the brane
electric charge and thus inherit some of their physical properties. The most
appealing property is their quantization: in d_\perp extra dimensions,
Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical
origin also explains the apparent fine-tuning required in the Randall-Sundrum
scenario. In our approach, the cosmological constants are derived parameters
and cannot be chosen arbitrarily; instead they are determined by the underlying
Lagrangian. Some of the branes we construct that support cosmological constant
in the bulk have supersymmetric properties: D3-branes of type IIB superstring
theory provide an explicit example.Comment: 17 pages, LaTeX, 1 figure. v2: references added and a comment about
D-8 brane of massive IIA sugra included v3: improved argument on the
effective cosmological constants quantization and clarified discussion on the
supersymmetric issue of the solutions constructed. Final version to appear in
NP
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