11,880 research outputs found
The 125 GeV Higgs and Electroweak Phase Transition Model Classes
Recently, the ATLAS and CMS detectors have discovered a bosonic particle
which, to a reasonable degree of statistical uncertainty, fits the profile of
the Standard Model Higgs. One obvious implication is that models which predict
a significant departure from Standard Model phenomenology, such as large exotic
(e.g., invisible) Higgs decay or mixing with a hidden sector scalar, are
already ruled out. This observation threatens the viability of electroweak
baryogenesis, which favors, for example, a lighter Higgs and a Higgs coupled to
or mixed with light scalars. To assess the broad impact of these constraints,
we propose a scheme for classifying models of the electroweak phase transition
and impose constraints on a class-by-class basis. We find that models, such as
the MSSM, which rely on thermal loop effects are severely constrained by the
measurement of a 125 GeV Higgs. Models which rely on tree-level effects from a
light singlet are also restricted by invisible decay and mixing constraints.
Moreover, we find that the parametric region favored by electroweak
baryogenesis often coincides with an enhanced symmetry point with a distinctive
phenomenological character. In particular, enhancements arising through an
approximate continuous symmetry are phenomenologically disfavored, in contrast
with enhancements from discrete symmetries. We also comment on the excess of
diphoton events observed by ATLAS and CMS. We note that although Higgs portal
models can accommodate both enhanced diphoton decay and a strongly first order
electroweak phase transition, the former favors a negative Higgs portal
coupling whereas the latter favors a positive one, and therefore these two
constraints are at tension with one another.Comment: 35 pages, 7 figure
Strongly First Order Phase Transitions Near an Enhanced Discrete Symmetry Point
We propose a group theoretic condition which may be applied to extensions of
the Standard Model in order to locate regions of parameter space in which the
electroweak phase transition is strongly first order, such that electroweak
baryogenesis may be a viable mechanism for generating the baryon asymmetry of
the universe. Specifically, we demonstrate that the viable corners of parameter
space may be identified by their proximity to an enhanced discrete symmetry
point. At this point, the global symmetry group of the theory is extended by a
discrete group under which the scalar sector is non-trivially charged, and the
discrete symmetry is spontaneously broken such that the discrete symmetry
relates degenerate electroweak preserving and breaking vacua. This idea is used
to investigate several specific models of the electroweak symmetry breaking
sector. The phase transitions identified through this method suggest
implications for other relics such as dark matter and gravitational waves.Comment: 17 pages, 4 figure
Production and state-selective detection of ultracold, ground state RbCs molecules
Using resonance-enhanced two-photon ionization, we detect ultracold,
ground-state RbCs molecules formed via photoassociation in a laser-cooled
mixture of 85Rb and 133Cs atoms. We obtain extensive bound-bound excitation
spectra of these molecules, which provide detailed information about their
vibrational distribution, as well as spectroscopic data on the RbCs ground
a^3\Sigma^+ and excited (2)^3\Sigma^+, (1)^1\Pi states. Analysis of this data
allows us to predict strong transitions from observed excited levels to the
absolute vibronic ground state of RbCs, potentially allowing the production of
stable, ultracold polar molecules at rates as large as 10^7 s^{-1}
Towards quantum gravity measurement by cold atoms
Peer reviewedPreprin
Mixed Statistics on 01-Fillings of Moon Polyominoes
We establish a stronger symmetry between the numbers of northeast and
southeast chains in the context of 01-fillings of moon polyominoes. Let \M be
a moon polyomino with rows and columns. Consider all the 01-fillings of
\M in which every row has at most one 1. We introduce four mixed statistics
with respect to a bipartition of rows or columns of \M. More precisely, let
and be the union of rows whose
indices are in . For any filling , the top-mixed (resp. bottom-mixed)
statistic (resp. ) is the sum of the number of
northeast chains whose top (resp. bottom) cell is in , together
with the number of southeast chains whose top (resp. bottom) cell is in the
complement of . Similarly, we define the left-mixed and
right-mixed statistics and , where is a subset
of the column index set . Let be any of these
four statistics , , and , we show that the joint distribution of the pair is symmetric and independent of the subsets . In
particular, the pair of statistics is
equidistributed with (\se(M),\ne(M)), where \se(M) and are the
numbers of southeast chains and northeast chains of , respectively.Comment: 20 pages, 6 figure
Optimum Shapes for Minimising Bond Stress in Scarf Repairs
Bonded scarf repairs are used in composite structures when high strength recovery is needed or when there is a requirement for a flush surface to satisfy aerodynamic or stealth requirements. However, scarf repairs are complex to design and require the removal of significant parent structure, particularly for thick skins. In this investigation, analytical and numerical approaches have been developed to investigate whether an optimum repair shape for a known biaxial load can be determined. The results clearly demonstrate that the strength of a repaired panel can be improved by optimising both the initial damage cut-out shape and the scarf angle distribution
Mithramycin forms a stable dimeric complex by chelating with Fe(II): DNA-interacting characteristics, cellular permeation and cytotoxicity
Mith (mithramycin) forms a 2:1 stoichiometry drugâmetal complex through the chelation with Fe(II) ion as studied using circular dichroism spectroscopy. The binding affinity between Mith and Fe(II) is much greater than other divalent metal ions, including Mg(II), Zn(II), Co(II), Ni(II) and Mn(II). The [(Mith)(2)âFe(II)] complex binds to DNA and induces a conformational change of DNA. Kinetic analysis of surface plasmon resonance studies revealed that the [(Mith)(2)âFe(II)] complex binds to DNA duplex with higher affinity compared with the [(Mith)(2)âMg(II)] complex. A molecular model of the Mith-DNAâMetal(II) complex is presented. DNA-break assay showed that the [(Mith)(2)âFe(II)] complex was capable of promoting the one-strand cleavage of plasmid DNA in the presence of hydrogen peroxide. Intracellular Fe(II) assays and fluorescence microscopy studies using K562 indicated that this dimer complex maintains its structural integrity and permeates into the inside of K562 cells, respectively. The [(Mith)(2)âFe(II)] complex exhibited higher cytotoxicity than the drug alone in some cancer cell lines, probably related to its higher DNA-binding and cleavage activity. Evidences obtained in this study suggest that the biological effects caused by the [(Mith)(2)âFe(II)] complex may be further explored in the future
Development of polymer composites using modiïŹed, high-structural integrity graphene platelets
Previous studies on polymer/graphene composites have mainly utilized either reduced graphene oxide or graphite nanoplatelets of over 10 nm in thickness. In this study we covalently modiïŹed 3-nm thick graphene platelets (GnPs) by the reaction between the GnPsâ epoxide groups and the end-amine groups of a commercial long-chain surfactant (Mw = 2000), compounded the modiïŹed GnPs (m-GnPs) with a model polymer epoxy, and investigated the structure and properties of both m-GnPs and their epoxy composites. A low Raman ID/IG ratio of 0.13 was found for m-GnPs corresponding to high structural integ-rity. A percolation threshold of electrical conductivity was observed at 0.32 vol% m-GnPs, and the 0.98 vol% m-GnPs improved the Youngâs modulus, fracture energy release rate and glass transition tem-perature of epoxy by 14%, 387% and 13%, respectively. These signiïŹcantly improved properties are cred-ited to: (i) the low Raman ID/IG ratio of GnPs, maximizing the structural integrity and thus conductivity, stiffness and strength inherited from its sister graphene, (ii) the low thickness of GnPs, minimizing the damaging effect of the poor through-plane mechanical properties and electrical conductivity of graphene,(iii) the high-molecular weight surfactant, leading to uniformly dispersed GnPs in the matrix, and (iv) a covalently bonded interface between m-GnPs and matrix, more effectively transferring load/electron across interface
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