1,068 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
Four-top production and tt + missing energy events at multi TeV e+e− colliders
Four-top production and top pair production in association with missing energy at e+e− colliders are sensitive probes of beyond-the-Standard-Model physics. We consider Standard Model extensions containing a new U(1)' which couples preferably to the most massive states of the SMsuch as the top quark or Dark Matter but has suppressed couplings to all the light states of the SM, as inspired by
Randall-Sundrum–like setups or theories of partial fermion compositeness. These simple models are poorly constrained by experimental data but lead to striking new signatures at colliders. In this paper we consider Z' �production in association with a top quark pair in 3TeV e+e− collisions at CLIC, leading to interesting four-top final states and tt + Emiss events
Gamma-ray lines and One-Loop Continuum from s-channel Dark Matter Annihilations
The era of indirect detection searches for dark matter has begun, with the
sensitivities of gamma-ray detectors now approaching the parameter space
relevant for weakly interacting massive particles. In particular, gamma ray
lines would be smoking gun signatures of dark matter annihilation, although
they are typically suppressed compared to the continuum. In this paper, we pay
particular attention to the 1-loop continuum generated together with the
gamma-ray lines and investigate under which conditions a dark matter model can
naturally lead to a line signal that is relatively enhanced. We study generic
classes of models in which DM is a fermion that annihilates through an
s-channel mediator which is either a vector or scalar and identify the coupling
and mass conditions under which large line signals occur. We focus on the
"forbidden channel mechanism" advocated a few years ago in the "Higgs in space"
scenario for which tree level annihilation is kinematically forbidden today.
Detailed calculations of all 1-loop annihilation channels are provided. We
single out very simple models with a large line over continuum ratio and
present general predictions for a large range of WIMP masses that are relevant
not only for Fermi and Hess II but also for the next generation of telescopes
such as CTA and Gamma-400. Constraints from the relic abundance, direct
detection and collider bounds are also discussed.Comment: 32 pages, 13 figures; v2: minor clarifications, summary paragraph
added; v3: matches published version, minor clarifications, results unchange
Saline lakes
Diatom assemblages are described from surface sediments in thirteen salt lakes located in the southern Bolivian Altiplano. Factor analysis of correspondences and cluster analysis are used to classify the diatom assemblages. New methods are proposed to establish the qualitative and quantitative relationships between diatom floras and ecological parameters. Diatom assemblages are linked more to the ionic elements than to the salinity, pH, depth, temperature or elevation. Environmental variables are divided into three modalities which allow considerations of many different variables not under the same units. (Résumé d'auteur
Поведение азота при выплавке специальных сталей в плазменно-дуговой печи переменного тока с керамическим подом
Предложены формулы для расчета стандартной растворимости азота в специальных сталях и никелевом сплаве. Построены политермы растворимости азота в исследуемых материалах. Экспериментально установлена зависимость механических свойств сталей 05Х12Н2М и 07Х12НМФБР от содержания в них азота.Formulae are offered for calculation of standard solubility of nitrogen in special steels and nickel alloy. Polytherms of nitrogen solubility in materials being investgated are plotted. The dependence of mechanical properties of steels 05Kh12N2M and 07Kh12NMFBR on nitrogen content in them was established experimentally
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