We consider a fully dynamical origin for the masses of weak gauge bosons and heavy quarks of the Standard Model. Electroweak symmetry breaking and the gauge boson masses arise from new strong ...dynamics, which leads to the appearance of a composite scalar in the spectrum of excitations. In order to generate mass for the Standard Model fermions, we consider extended gauge dynamics, effectively represented by four fermion interactions at presently accessible energies. By systematically treating these interactions, we show that they lead to a large reduction of the mass of the scalar resonance. Therefore, interpreting the scalar as the recently observed 125 GeV state implies that the mass originating solely from new strong dynamics can be much heavier, i.e. of the order of 1 TeV. In addition to reducing the mass of the scalar resonance, we show that the four-fermion interactions allow for contributions to the oblique corrections in agreement with the experimental constraints. The couplings of the scalar resonance with the Standard Model gauge bosons and fermions are evaluated, and found to be compatible with the current LHC results. Additional new resonances are expected to be heavy, with masses of the order of a few TeVs, and hence accessible in future experiments.
Extra-dimensional Higgsless models with electroweak symmetry breaking through boundary conditions generically have difficulties with electroweak precision constraints, when the fermions are localized ...to the “branes” in the fifth dimension. In this Letter we show that these constraints can be relaxed by allowing the light fermions to have a finite extent into the bulk of the fifth dimension. The T and U electroweak parameters can be naturally suppressed by a custodial symmetry, while the S parameter can be made to vanish through a cancellation, if the leakage into the bulk of the light gauge fields and the light left-handed fermion fields are of the same size. This cancellation is possible while allowing realistic values for the first two generations of fermion masses, although special treatment is probably required for the top quark. We present this idea here in the context of a specific continuum theory-space model; however, it can be applied to any five-dimensional Higgsless model, either with a flat or a warped background.
We present a new Little Higgs model, motivated by the deconstruction of a five-dimensional gauge-Higgs model. The approximate global symmetry is SO(5)
0
× SO(5)
1
, breaking to SO(5), with a gauged ...subgroup of SU(2)
0
L
× U(1)
0
R
×
O
(4)
1
, breaking to SU(2)
L
×U(1)
Y
. Radiative corrections produce an additional small vacuum misalignment, breaking the electroweak symmetry down to U(1)
EM
. Novel features of this model are: the only un-eaten pseudo-Goldstone boson in the effective theory is the Higgs boson; the model contains a custodial symmetry, which ensures that
at tree-level; and the potential for the Higgs boson is generated entirely through one-loop radiative corrections. A small negative mass-squared in the Higgs potential is obtained by a cancellation between the contribution of two heavy partners of the top quark, which is readily achieved over much of the parameter space. We can then obtain both a vacuum expectation value of
v
= 246 GeV and a light Higgs boson mass, which is strongly correlated with the masses of the two heavy top quark partners. For a scale of the global symmetry breaking of
f
= 1 TeV and using a single cutoff for the fermion loops, the Higgs boson mass satisfies 120 GeV ≲
M
H
≲ 150 GeV over much of the range of parameter space. For
f
raised to 10 TeV, these values increase by about 40 GeV. Effects at the ultraviolet cutoff scale may also raise the predicted values of the Higgs boson mass, but the model still favors
M
H
≲ 200GeV.
Assuming that the observed Higgs-like resonance at the Large Hadron Collider is a technicolor isosinglet scalar (the technicolor Higgs), we argue that the standard model top-induced radiative ...corrections reduce its mass toward the desired experimental value. We discuss conditions for the spectrum of technicolor theories to feature a technicolor Higgs with the phenomenologically required dynamical mass. We consider different representations under the technicolor gauge group and employ scaling laws in terms of the dimension of the representation. We also summarize the potential effects of walking dynamics on the mass of the technicolor Higgs.
We study a chiral quark model of
π
,
σ
,
ρ
, and
a
1
mesons in the large-
N
c
limit. We show that the quadratic
a
1
−
π
mixing can be set to zero at zero momentum, thus protecting the
g
σππ
and
g
ρππ
...couplings from being contaminated by the corresponding vertices with one or both pions replaced by the axial-vector meson. We further require the chiral-quark Lagrangian to feature an approximate classical scale invariance, the latter being only broken by dimension-two mass terms, and that the longitudinal vector meson scattering amplitudes grow at most like
s
, where √
s
is the center-of-mass energy. This allows us to accurately predict the correct value of
g
σππ
,
g
ρππ
, and the
a
1
decay constant
. We further show that strongly coupled theories with near-conformal dynamics are expected to feature an approximate custodial chiral symmetry, with interesting phenomenological consequences.
For rate determinations of anaerobic metabolism it is essential to maintain strictly anoxic conditions throughout the experiment. However, even if oxygen contamination can be avoided while preparing ...the incubation containers, it is still possible that the incubation containers themselves contaminate the samples by oxygen diffusing from or through their plastic or rubber components. In this study, we investigated the sources and extent of oxygen contamination during anoxic incubations, and present solutions to minimize oxygen contamination. In particular, we investigated oxygen contamination in Labco® Exetainers, glass vials with a butyl rubber septum in the screw cap, which are frequently used in microbiological experiments. Our results show that significant oxygen contamination occurred at different stages during the incubation. Contamination occurred when Exetainers were either filled or incubated for more than 16
h under oxic atmosphere, but also under an oxygen-free atmosphere due to diffusion of oxygen out of the butyl rubber septum. Therefore, to avoid oxygen contamination during incubations, we suggest (1) filling and incubating the incubation containers under anoxic atmosphere (glove bag) and (2) deoxygenating all elastomers in sample processing and incubation equipment. If initial oxygen contamination cannot be avoided, introduction of an anoxic headspace might help extract oxygen from the incubated sample and present a buffer against oxygen diffusing out of the septum. We modeled the amount of oxygen diffusing out of butyl rubber septa under different conditions, and results fitted well with the observed oxygen contamination. Thus, the model can be used to predict oxygen contamination under varying conditions and for differently sized septa.
► Oxygen leaking out of rubber seals contaminates anoxic samples during incubations. ► The degree of oxygen contamination was modeled. ► The model was verified with experiments. ► Solutions are provided to diminish oxygen contamination from rubber seals.
Technicolor Higgs boson in the light of LHC data Belyaev, Alexander; Brown, Matthew S.; Foadi, Roshan ...
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2014, Letnik:
90, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We consider scenarios in which the 125 GeV resonance observed at the Large Hadron Collider is a Technicolor (TC) isosinglet scalar, the TC Higgs and explore the viable parameter space of the ...effective Higgs boson couplings within the TC Higgs scenario using the latest LHC data. By comparison with quantum chromodynamics, we argue that the couplings of the TC Higgs to the massive weak bosons are very close to the standard model (SM) values. The couplings to photons and gluons are model-dependent, but close to the SM values in several TC theories. The couplings of the TC Higgs to SM fermions are due to interactions beyond TC, such as extended technicolor: if such interactions successfully generate mass for the SM fermions, we argue that the couplings of the latter to the TC Higgs are also SM-like. We suggest a generic parametrization of the TC Higgs interactions with SM particles that accommodates a large class of TC models, and we perform a fit of these parameters to the Higgs LHC data. The fit reveals regions of the parameter space where the form factors have an order-one absolute value at the 95% CL, in agreement with expectations in TC theories. This indicates that the discovered Higgs boson is consistent with the TC Higgs hypothesis for several TC theories.
125 GeV Higgs from a chiral techniquark model Di Chiara, Stefano; Foadi, Roshan; Tuominen, Kimmo
Physical review. D, Particles, fields, gravitation, and cosmology,
12/2014, Letnik:
90, Številka:
11
Journal Article
Recenzirano
Odprti dostop
We consider the spin-zero spectrum of a strongly coupled gauge theory. In particular, we focus on the dynamical mass of the isosinglet scalar resonance in the presence of a four-fermion interaction ...external to the gauge dynamics. This is motivated by the extended technicolor framework for dynamical electroweak symmetry breaking. Applying the large-N limit, we sum all the leading-order contributions, and find that the corrections to the mass of the isosinglet scalar resonance can be large, potentially reducing its value from O(1) TeV to the observed value of 125 GeV.
We assess current experimental constraints on the bidoublet+singlet model of top compositeness previously proposed in the literature. This model extends the Standard Model's spectrum by adding a ...custodially embedded vectorlike electroweak bidoublet of quarks and a vectorlike electroweak singlet quark. While either of those states alone would produce a model in tension with constraints from precision electroweak data, in combination they can produce a viable model. We show that current precision electroweak data, in the wake of the Higgs discovery, accommodate the model and we explore the impact of direct collider searches for the partners of the top quark.
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