4,868 research outputs found
Global fit to Higgs signal strengths and couplings and implications for extended Higgs sectors
The most recent LHC data have provided a considerable improvement in the
precision with which various Higgs production and decay channels have been
measured. Using all available public results from ATLAS, CMS and the Tevatron,
we derive for each final state the combined confidence level contours for the
signal strengths in the (gluon fusion + ttH associated production) versus
(vector boson fusion + VH associated production) space. These "combined signal
strength ellipses" can be used in a simple, generic way to constrain a very
wide class of New Physics models in which the couplings of the Higgs boson
deviate from the Standard Model prediction. Here, we use them to constrain the
reduced couplings of the Higgs boson to up-quarks, down-quarks/leptons and
vector boson pairs. We also consider New Physics contributions to the
loop-induced gluon-gluon and photon-photon couplings of the Higgs, as well as
invisible/unseen decays. Finally, we apply our fits to some simple models with
an extended Higgs sector, in particular to Two-Higgs-Doublet models of Type I
and Type II, the Inert Doublet model, and the Georgi-Machacek triplet Higgs
model.Comment: 31 pages, 15 figures; v2: fixed important factor of 2 missing in Eq.
(1) (results unchanged), extended discussion in the next-to-last paragraph of
Section 3, some references added; v3: appendices and references added,
matches version accepted by PR
Status of invisible Higgs decays
We analyze the extent to which the LHC and Tevatron results as of the end of
2012 constrain invisible (or undetected) decays of the Higgs boson-like state
at ~ 125 GeV. To this end we perform global fits for several cases: 1) a Higgs
boson with Standard Model (SM) couplings but additional invisible decay modes;
2) SM couplings to fermions and vector bosons, but allowing for additional new
particles modifying the effective Higgs couplings to gluons and photons; 3) no
new particles in the loops but tree-level Higgs couplings to the up-quarks,
down-quarks and vector bosons, relative to the SM, treated as free parameters.
We find that in the three cases invisible decay rates of 23%, 61%, 88%,
respectively, are consistent with current data at 95% confidence level (CL).
Limiting the coupling to vector bosons, CV, to CV < 1 in case 3) reduces the
allowed invisible branching ratio to 56% at 95% CL. Requiring in addition that
the Higgs couplings to quarks have the same sign as in the SM, an invisible
rate of up to 36% is allowed at 95% CL. We also discuss direct probes of
invisible Higgs decays, as well as the interplay with dark matter searches.Comment: 14 pages, 8 figures; v2: extended discussion on ZH associated
production, references added, minor corrections; v4: matches final version
published in Phys. Lett.
Higgs Couplings at the End of 2012
Performing a fit to all publicly available data, we analyze the extent to
which the latest results from the LHC and Tevatron constrain the couplings of
the Higgs boson-like state at ~ 125 GeV. To this end we assume that only
Standard Model (SM) particles appear in the Higgs decays, but tree-level Higgs
couplings to the up-quarks, down-quarks and vector bosons, relative to the SM
are free parameters. We also assume that the leptonic couplings relative to the
SM are the same as for the down-quark, and a custodial symmetry for the V=W,Z
couplings. In the simplest approach, the effective Higgs couplings to gluons
and photons are computed in terms of the previous parameters. This approach is
also applied to Two-Higgs-Doublet Models of Type I and Type II. However, we
also explore the possibility that the net Higgs to gluon-gluon and gamma-gamma
couplings have extra loop contributions coming from Beyond-the-Standard Model
physics. We find that the SM p-value ~ 0.5 is more than 2 sigma away from fits
in which: a) there is some non-SM contribution to the gamma-gamma coupling of
the Higgs; or b) the sign of the top quark coupling to the Higgs is opposite
that of the W coupling. In both these cases p-values ~ 0.9 can be achieved.
Since option b) is difficult to realize in realistic models, it would seem that
new physics contributions to the effective couplings of the Higgs are
preferred.Comment: 25 pages, 11 figures; v2: minor corrections, references added; v3:
acknowledgement adde
The Origin of Fe II Emission in AGN
We used a very large set of models of broad emission line (BEL) clouds in AGN
to investigate the formation of the observed Fe II emission lines. We show that
photoionized BEL clouds cannot produce both the observed shape and observed
equivalent width of the 2200-2800A Fe II UV bump unless there is considerable
velocity structure corresponding to a microturbulent velocity parameter v_turb
> 100 km/s for the LOC models used here. This could be either microturbulence
in gas that is confined by some phenomenon such as MHD waves, or a velocity
shear such as in the various models of winds flowing off the surfaces of
accretion disks. The alternative way that we can find to simultaneously match
both the observed shape and equivalent width of the Fe II UV bump is for the Fe
II emission to be the result of collisional excitation in a warm, dense gas.
Such gas would emit very few lines other than Fe II. However, since the
collisionally excited gas would constitute yet another component in an already
complicated picture of the BELR, we prefer the model involving turbulence. In
either model, the strength of Fe II emission relative to the emission lines of
other ions such as Mg II depends as much on other parameters (either v_turb or
the surface area of the collisionally excited gas) as it does on the iron
abundance. Therefore, the measurement of the iron abundance from the FeII
emission in quasars becomes a more difficult problem.Comment: 23 pages. Accepted by Ap
Radar Detection of High Concentrations of Ice Particles - Methodology and Preliminary Flight Test Results
High Ice Water Content (HIWC) has been identified as a primary causal factor in numerous engine events over the past two decades. Previous attempts to develop a remote detection process utilizing modern commercial radars have failed to produce reliable results. This paper discusses the reasons for previous failures and describes a new technique that has shown very encouraging accuracy and range performance without the need for any hardware modifications to industrys current radar designs. The performance of this new process was evaluated during the joint NASA/FAA HIWC RADAR II Flight Campaign in August of 2018. Results from that evaluation are discussed, along with the potential for commercial application, and development of minimum operational performance standards for a future commercial radar product
Chemical and dynamical processes in the mesospheric emissive layer. First results of stereoscopic observations
[1] The mesospheric emissive layer is an efficient tracer of the dynamical processes propagating in the atmosphere at that level. CCD images in the near infrared taken from the ground at slant angles often reveal the existence of wavy fields. A series of such images has been transformed, using matrix operations, producing a downward satellite-type view that covers a circular area of radius ∼1000 km at the altitude of the layer. The Fourier characteristics of the wave system are measured using a Morlet-type wavelet generator function with horizontal wavelengths of mostly ∼20–40 km and 100–150 km and temporal periods of ∼15–30 min. An oxygen-hydrogen model is used to evaluate the response of the emissive layer to a progressive density wave. The altitude of the layer is modulated with an amplitude of ∼0.8–1.8 km when a density wave propagates vertically. The layer thickness is slightly modulated and is equal to ∼7 km. Stereoscopic pairs of photographs taken simultaneously on 8–9 September 2000 at the Château-Renard and Pic du Midi observatories are used to obtain surface maps of the emission layer barycenter altitude. A stereocorrelation method suitable for low contrast objects without discrete contours is employed. Preliminary results for areas ∼50 × 50 km2 are presented. The surface maps of the layer barycenter altitude depict the existence of waves. They show the same wavy structure and compare favorably with the maps showing the emission intensity
Radial Fredholm perturbation in the two-dimensional Ising model and gap-exponent relation
We consider concentric circular defects in the two-dimensional Ising model,
which are distributed according to a generalized Fredholm sequence, i. e. at
exponentially increasing radii. This type of aperiodicity does not change the
bulk critical behaviour but introduces a marginal extended perturbation. The
critical exponent of the local magnetization is obtained through finite-size
scaling, using a corner transfer matrix approach in the extreme anisotropic
limit. It varies continuously with the amplitude of the modulation and is
closely related to the magnetic exponent of the radial Hilhorst-van Leeuwen
model. Through a conformal mapping of the system onto a strip, the gap-exponent
relation is shown to remain valid for such an aperiodic defect.Comment: 12 pages, TeX file + 4 figures, epsf neede
Human thyroid tumours, the puzzling lessons from E7 and RET/PTC3 transgenic mice
Human rearranged RET/PTC3 (papillary thyroid carcinoma) proto-oncogene and high-risk human papillomavirus (HPV) type 16 E7 oncogene induces in the mouse a neoplastic transformation of thyroid follicular cells. We present a detailed immuno-histological study (170 mouse thyroids: RET/PTC3, E7, wild type, 2- to 10-month-old) with cell cycle proliferation and signalling pathway indicators. The characteristics of both models are different. There is an ‘oncogene dependent' cellular signature, maintained at all studied ages in the E7 model, less in the RET/PTC3 model. During tumour development a large heterogeneity occurred in the Tg-RET/PTC3 model within a same tumour or within a same thyroid lobe. The Tg-E7 model was less heterogeneous, with a dominant goitrous pattern. The solid tumour already described in the RET/PTC3 models associated with cribriform patterns, suggested ‘PTC spindle cell changes' as in humans PTC rather than the equivalent of the solid human PTC. Proliferation and apoptosis in the two thyroid models are related to the causal oncogene rather than reflect a general tumorigenic process. The thyroids of RET/PTC3 mice appeared as a partial and transient model of human PTCs, whereas the Tg-E7 mice do not belong to the usual PTC type
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