55 research outputs found
Effects of Top-quark Compositeness on Higgs Boson Production at the LHC
Motivated by the possibility that the right-handed top-quark (t_R) is
composite, we discuss the effects of dimension-six operators on the Higgs boson
production at the LHC. When t_R is the only composite particle among the
Standard Model (SM) particles, the (V+A)\otimes (V+A) type four-top-quark
contact interaction is expected to have the largest coefficient among the
dimension-six operators, according to the Naive Dimensional Analysis (NDA). We
find that, to lowest order in QCD and other SM interactions, the cross section
of the SM Higgs boson production via gluon fusion does not receive corrections
from one insertion of the new contact interaction vertex. We also discuss the
effects of other dimension-six operators whose coefficients are expected to be
the second and the third largest from NDA. We find that the operator which
consists of two t_R's and two SM Higgs boson doublets can recognizably change
the Higgs boson production cross section from the SM prediction if the cut-off
scale is \sim 1TeV.Comment: 12 pages, 7 figures. v2: explanations improved in Section 3, other
minor changes. Version published in JHE
Analysis of techni-dilaton as a dark matter candidate
The almost conformal dynamics of walking technicolor (TC) implies the
existence of the approximate scale invariance, which breaks down spontaneously
by the condensation of anti-techni and techni-fermions. According to the
Goldstone theorem, a spinless, parity-even particle, called techni-dilaton
(TD), then emerges at low energy. If TC exhibits an extreme walking, TD mass is
parametrically much smaller than that of techni-fermions (around 1 TeV), while
its decay constant is comparable to the cutoff scale of walking TC. We analyze
the light, decoupled TD as a dark matter candidate and study cosmological
productions of TD, both thermal and non-thermal, in the early Universe. The
thermal population is governed dominantly by single TD production processes
involving vertices breaking the scale symmetry, while the non-thermal
population is by the vacuum misalignment and is accumulated via harmonic and
coherent oscillations of misaligned classical TD fields. The non-thermal
population turns out to be dominant and large enough to explain the abundance
of presently observed dark matter, while the thermal population is highly
suppressed due to the large TD decay constant. Several cosmological and
astrophysical limits on the light, decoupled TD are examined to find that the
TD mass is constrained to be in a range between 0.01 eV and 500 eV. From the
combined constraints on cosmological productions and astrophysical
observations, we find that the light, decoupled TD can be a good dark matter
candidate with the mass around a few hundreds of eV for typical models of
(extreme) walking TC. We finally mention possible designated experiments to
detect the TD dark matter.Comment: 26 pages. 16 figures; v2, expanded Section 2.4 on composite Higgs in
light of newly discovered Higgs-like particle at LH
Linear confinement without dilaton in bottom-up holography for walking technicolour
In PRD78(2008)055005 [arXiv:0805.1503 [hep-ph]] and PRD79(2009)075004
[arXiv:0809.1324 [hep-ph]], we constructed a holographic description of walking
technicolour theories using both a hard- and a soft-wall model. Here, we show
that the dilaton field becomes phenomenologically irrelevant for the spectrum
of spin-one resonances once a term is included in the Lagrangian that mixes the
Goldstone bosons and the longitudinal components of the axial vector mesons. We
show how this mixing affects our previous results and we make predictions about
how this description of technicolour can be tested.Comment: 7 pages, no figure
On the gauge boson's properties in a candidate technicolor theory
The technicolor scenario replaces the Higgs sector of the standard model with
a strongly interacting sector. One candidate for a realization of such a sector
is two-technicolor Yang-Mills theory coupled to two degenerate flavors of
adjoint, massless techniquarks. Using lattice gauge theory the properties of
the technigluons in this scenario are investigated as a function of the
techniquark mass towards the massless limit. For that purpose the minimal
Landau gauge two-point and three-point correlation functions are determined,
including a detailed systematic error analysis. The results are, within the
relatively large systematic uncertainties, compatible with a behavior very
similar to QCD at finite techniquark mass. However, the limit of massless
techniquarks exhibits features which could be compatible with a
(quasi-)conformal behavior.Comment: 27 pages, 17 figures, 1 table; v2: persistent notational error
corrected, some minor modification
Scaling laws near the conformal window of many-flavor QCD
We derive universal scaling laws for physical observables such as the
critical temperature, the chiral condensate, and the pion decay constant as a
function of the flavor number near the conformal window of many-flavor QCD in
the chiral limit. We argue on general grounds that the associated critical
exponents are all interrelated and can be determined from the critical exponent
of the running gauge coupling at the Caswell-Banks-Zaks infrared fixed point.
We illustrate our findings with the aid of nonperturbative functional
Renormalization Group (RG) calculations and low-energy QCD models.Comment: 18 pages, 4 figures, references added and discussion expanded
(matches JHEP version
Conformal gauge-Yukawa theories away from four dimensions
We present the phase diagram and associated fixed points for a wide class of Gauge-Yukawa theories in d=4+ϵ dimensions. The theories we investigate involve non-abelian gauge fields, fermions and scalars in the Veneziano-Witten limit. The analysis is performed in steps, we start with QCD d and then we add Yukawa interactions and scalars which we study at next-to- and next-to-next-to-leading order. Interacting infrared fixed points naturally emerge in dimensions lower than four while ultraviolet ones appear above four. We also analyse the stability of the scalar potential for the discovered fixed points. We argue for a very rich phase diagram in three dimensions while in dimensions higher than four certain Gauge-Yukawa theories are ultraviolet complete because of the emergence of an asymptotically safe fixed point
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