28 research outputs found
Light Composite Higgs from Higher Representations versus Electroweak Precision Measurements -- Predictions for LHC
We investigate theories in which the technifermions in higher dimensional
representations of the technicolor gauge group dynamically break the
electroweak symmetry of the standard model. For the two-index symmetric
representation of the gauge group the lowest number of techniflavors needed to
render the underlying gauge theory quasi conformal is two. We confront the
models with the recent electroweak precision measurements and demonstrate that
the two technicolor theory is a valid candidate for a dynamical breaking of the
electroweak symmetry. The electroweak precision measurements provide useful
constraints on the relative mass splitting of the new leptons needed to cure
the Witten anomaly. In the case of a fourth family of leptons with ordinary
lepton hypercharge the new heavy neutrino can be a natural candidate of cold
dark matter. We also propose theories in which the critical number of flavors
needed to enter the conformal window is higher than the one with fermions in
the two-index symmetric representation, but lower than in the walking
technicolor theories with fermions only in the fundamental representation of
the gauge group. Due to the near conformal/chiral phase transition, we show
that the composite Higgs is very light compared to the intrinsic scale of the
technicolor theory. For the two technicolor theory we predict the composite
Higgs mass not to exceed 150 GeV.Comment: RevTex, 53 pages, 7 figures and two table
Minimal Super Technicolor
We introduce novel extensions of the Standard Model featuring a
supersymmetric technicolor sector. First we consider N=4 Super Yang-Mills which
breaks to N=1 via the electroweak (EW) interactions and coupling to the MSSM.
This is a well defined, economical and calculable extension of the SM involving
the smallest number of fields. It constitutes an explicit example of a natural
supersymmetric conformal extension of the Standard Model featuring a well
defined connection to string theory. It allows to interpolate, depending on how
we break the underlying supersymmetry, between unparticle physics and Minimal
Walking Technicolor. As a second alternative we consider other N =1 extensions
of the Minimal Walking Technicolor model. The new models allow all the standard
model matter fields to acquire a mass.Comment: Improved version demonstrating that this extension is
phenomenologically viable. No Landau pole exists in the theory to two loops
level. This is the first theory showing that supersymmetry can solve the
flavor problem when coupled to low energy technicolo
Confinement and Chiral Symmetry
We illustrate why color deconfines when chiral symmetry is restored in gauge
theories with quarks in the fundamental representation, and while these
transitions do not need to coincide when quarks are in the adjoint
representation, entanglement between them is still present.Comment: 4 pages, 1 figure, proceedings of Quark Matter 200
Induced Universal Properties and Deconfinement
We propose a general strategy to determine universal properties induced by a
nearby phase transition on a non-order parameter field. A general
renormalizable Lagrangian is used, which contains the order parameter and a
non-order parameter field, and respects all the symmetries present. We
investigate the case in which the order parameter field depends only on space
coordinates and the case in which this field is also time dependent. We find
that the spatial correlators of the non-order parameter field, in both cases,
are infrared dominated and can be used to determine properties of the phase
transition. We predict a universal behavior for the screening mass of a generic
singlet field, and show how to extract relevant information from such a
quantity. We also demonstrate that the pole mass of the non-order parameter
field is not infrared sensitive. Our results can be applied to any continuous
phase transition. As an example we consider the deconfining transition in pure
Yang-Mills theory, and show that our findings are supported by lattice data.
Our analysis suggests that monitoring the spatial correlators of different
hadron species, more specifically the derivatives of these, provides an
efficient and sufficient way to experimentally uncover the deconfining phase
transition and its features.Comment: Added computational details and improved the text. The results are
unchange
Tetracritical behavior in strongly interacting theories
We suggest a tetracritical fixed point to naturally occur in strongly
interacting theories. As a fundamental example we analyze the
temperature--quark chemical potential phase diagram of QCD with fermions in the
adjoint representation of the gauge group (i.e. adjoint QCD). Here we show that
such a non trivial multicritical point exists and is due to the interplay
between the spontaneous breaking of a global U(1) symmetry and the center group
symmetry associated to confinement. Our results demonstrate that taking
confinement into account is essential for understanding the critical behavior
as well as the full structure of the phase diagram of adjoint QCD. This is in
contrast to ordinary QCD where the center group symmetry associated to
confinement is explicitly broken when the quarks are part of the theory.Comment: RevTex, 5 figures. Final version to appear in PR
Spontaneous symmetry breaking in gauge theories via Bose-Einstein condensation
We propose a mechanism naturally leading to the spontaneous symmetry breaking
in a gauge theory. The Higgs field is assumed to have global and gauged
internal symmetries. We associate a non zero chemical potential to one of the
globally conserved charges commuting with all of the gauge transformations.
This induces a negative mass squared for the Higgs field triggering the
spontaneous symmetry breaking of the global and local symmetries. The mechanism
is general and we test the idea for the electroweak theory in which the Higgs
sector is extended to possess an extra global Abelian symmetry. To this
symmetry we associate a non zero chemical potential. The Bose-Einstein
condensation of the Higgs leads, at tree level, to modified dispersion
relations for the Higgs field while the dispersion relations of the gauge
bosons and fermions remain undisturbed. The latter are modified through higher
order corrections. We have computed some corrections to the vacuum
polarizations of the gauge bosons and fermions. To quantify the corrections to
the gauge boson vacuum polarizations with respect to the Standard Model we
considered the effects on the T parameter. We finally derive the one loop
modified fermion dispersion relations.Comment: RevTeX 4, 13 pages. Added references and corrected typo
Unnatural Origin of Fermion Masses for Technicolor
We explore the scenario in which the breaking of the electroweak symmetry is
due to the simultaneous presence and interplay of a dynamical sector and an
unnatural elementary Higgs. We introduce a low energy effective Lagrangian and
constrain the various couplings via direct search limits and electroweak and
flavor precision tests. We find that the model we study is a viable model of
dynamical breaking of the electroweak symmetry.Comment: 20 pages, 7 eps figure
Determining the conformal window: SU(2) gauge theory with N_f = 4, 6 and 10 fermion flavours
We study the evolution of the coupling in SU(2) gauge field theory with
, 6 and 10 fundamental fermion flavours on the lattice. These values are
chosen close to the expected edges of the conformal window, where the theory
possesses an infrared fixed point. We use improved Wilson-clover action, and
measure the coupling in the Schr\"odinger functional scheme. At four flavours
we observe that the couping grows towards the infrared, implying QCD-like
behaviour, whereas at ten flavours the results are compatible with a Banks-Zaks
type infrared fixed point. The six flavour case remains inconclusive: the
evolution of the coupling is seen to become slower at the infrared, but the
accuracy of the results falls short from fully resolving the fate of the
coupling. We also measure the mass anomalous dimension for the case.Comment: 22 pages, 12 figures. Proof readin
Invisible Higgs and Dark Matter
We investigate the possibility that a massive weakly interacting fermion
simultaneously provides for a dominant component of the dark matter relic
density and an invisible decay width of the Higgs boson at the LHC. As a
concrete model realizing such dynamics we consider the minimal walking
technicolor, although our results apply more generally. Taking into account the
constraints from the electroweak precision measurements and current direct
searches for dark matter particles, we find that such scenario is heavily
constrained, and large portions of the parameter space are excluded.Comment: arXiv admin note: text overlap with arXiv:0912.229
Bose-Einstein Condensation, Dark Matter and Acoustic Peaks
Scalar mediated interactions among baryons extend well above the Compton
wavelength, when they are embedded in a Bose-Einstein condensate composed of
the mediating particles. Indeed, this non-trivial environment results in an
infinite-ranged interaction. We show that if the Dark Matter of the Universe is
composed of such a condensate, the imprints of an interaction between baryonic
and Dark Matter could be manifest as anomalies in the peak structure of the
Cosmic Microwave Background.Comment: 11 pages, 2 figures; changes reflect published versio