1,759 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
Modeling the Biomass Production of Grasslands of Wallonia According to their Functional Type
Permanent grasslands are complex ecosystems which respond with a great variability - in terms of specific richness - to soil type and management strategies. Modelling is a valuable tool to explore these relationships. Our work consisted in adapting the Moorepark St Gilles grass growth model (MoSt GG) designed to model Lolium perenne plant functional type (PFT) pastures (PFT A) to a different PFT (Dactylis glomerata, PFT B) through literature-based parametrization. The model was evaluated under Walloon (Belgium) conditions using growth trials from 2014 to 2018 in two sites with contrasting pedo-climatic conditions. Three to five cuts were performed over the course of the growing seasons depending on the rainfall yielding a total of 20 and 25 biomass measurements (kg of DM per ha), for PFT A and B respectively. No site effects were observed in the performance of the model. The relative root mean square error (RRMSE), normalized deviation (ND) and model efficiency (EF) across all cuts, sites and PFTs were 33%, 3% and 68% respectively. PFT B was better simulated than A for the criteria RRMSE (33% vs 33%), ND (4% vs. 9%), and EF (75% vs. 54%). Although this first evaluation was satisfactory, a complementary parametrization for additional pedoclimatic conditions and PFTs is called for to use the model under the diversity of Walloon condition
Narrativity in complex systems
Humans use narrative for making sense of their environment. In this chapter we ask if, and if so how and to what extent, our narrative mind can help us deal scientifically with complexity. In order to answer this question, and to show what this means for education, we discuss fundamental aspects of narrative understanding of dynamical systems by working on a concrete story. These aspects involve perception of complex systems, experientiality of narrative, decomposition of systems into mechanisms, perception of forces of nature in mechanisms, and the relation of story-worlds to modelling-worlds, particularly in so-called ephemeral mechanisms. In parallel to describing fundamental issues, we develop a practical heuristic strategy for dealing with complex systems in five steps. (1) Systems thinking: Identify phenomena and foreground a system associated with these phenomena. (2) Mechanisms: Find and describe mechanisms responsible for these phenomena. (3) Forces of nature: Learn to perceive forces of nature as agents acting in these mechanisms. (4) Story-worlds and models: Learn how to use stories of forces (of nature) to construct story-worlds; translate the story-worlds into dynamical-model-worlds. (5) Ephemeral mechanisms for one-time, shortlived, unpredictable, and historical (natural) events: Learn how to create and accept ephemeral story-worlds and models. Ephemeral mechanisms and ephemeral story-worlds are a means for dealing with unpredictability inherent in complex dynamical systems. We argue that unpredictability does not fundamentally deny storytelling, modelling, explanation, and understanding of natural complex systems
On the presentation of the LHC Higgs Results
We put forth conclusions and suggestions regarding the presentation of the
LHC Higgs results that may help to maximize their impact and their utility to
the whole High Energy Physics community.Comment: Conclusions from the workshops "Likelihoods for the LHC Searches",
21-23 January 2013 at CERN, "Implications of the 125 GeV Higgs Boson", 18-22
March 2013 at LPSC Grenoble, and from the 2013 Les Houches "Physics at TeV
Colliders" workshop. 16 pages, 3 figures. Version 2: Comment added on the
first publication of signal strength likelihoods in digital form by ATLA
Aperiodic Ising Quantum Chains
Some years ago, Luck proposed a relevance criterion for the effect of
aperiodic disorder on the critical behaviour of ferromagnetic Ising systems. In
this article, we show how Luck's criterion can be derived within an exact
renormalisation scheme for Ising quantum chains with coupling constants
modulated according to substitution rules. Luck's conjectures for this case are
confirmed and refined. Among other outcomes, we give an exact formula for the
correlation length critical exponent for arbitrary two-letter substitution
sequences with marginal fluctuations of the coupling constants.Comment: 27 pages, LaTeX, 1 Postscript figure included, using epsf.sty and
amssymb.sty (one error corrected, some minor changes
Photoinduced 3D orientational order in side chain liquid crystalline azopolymers
We apply experimental technique based on the combination of methods dealing
with principal refractive indices and absorption coefficients to study the
photoinduced 3D orientational order in the films of liquid crystalline (LC)
azopolymers. The technique is used to identify 3D orientational configurations
of trans azobenzene chromophores and to characterize the degree of ordering in
terms of order parameters. We study two types of LC azopolymers which form
structures with preferred in-plane and out-of-plane alignment of
azochromophores, correspondingly. Using irradiation with the polarized light of
two different wavelengths we find that the kinetics of photoinduced anisotropy
can be dominated by either photo-reorientation or photoselection mechanisms
depending on the wavelength. We formulate the phenomenological model describing
the kinetics of photoinduced anisotropy in terms of the isomer concentrations
and the order parameter tensor. We present the numerical results for absorption
coefficients that are found to be in good agreement with the experimental data.
The model is also used to interpret the effect of changing the mechanism with
the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure
Local critical behaviour at aperiodic surface extended perturbation in the Ising quantum chain
The surface critical behaviour of the semi--infinite one--dimensional quantum
Ising model in a transverse field is studied in the presence of an aperiodic
surface extended modulation. The perturbed couplings are distributed according
to a generalized Fredholm sequence, leading to a marginal perturbation and
varying surface exponents. The surface magnetic exponents are calculated
exactly whereas the expression of the surface energy density exponent is
conjectured from a finite--size scaling study. The system displays surface
order at the bulk critical point, above a critical value of the modulation
amplitude. It may be considered as a discrete realization of the Hilhorst--van
Leeuwen model.Comment: 13 pages, TeX file + 6 figures, epsf neede
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