arXiv subjects

A. Doff

Publications and source records attributed to A. Doff.

At least 37 records · Page 2Linked to original sources

arXiv2018

Schwinger-Dyson equation boundary conditions induced by ETC radiative corrections

The technicolor (TC) Schwinger-Dyson equations (SDE) should include radiative corrections induced by extended technicolor (ETC) interactions when TC is embedded into a larger theory including also QCD. These radiative corrections couple the different strongly interacting Dyson equations. We discuss how the boundary conditions of the coupled SDE system are modified by these corrections, and verify that the ultraviolet behavior of the self-energies are described by a function that decreases logarithmically with momentum.

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arXiv2018

Extreme walking behavior and SDE boundary conditions in a 331-TC model

The solution of the phenomenological problems of technicolor (TC) models may reside in the different dynamical behavior of the technifermions self-energy appearing in walking (or quasi-conformal) theories. Motivated by recent results where it is shown how the boundary conditions (bc) of the anharmonic oscillator representation of the Schwinger-Dyson gap equation (SDE) to $SU(N)$ are directly related with the mass anomalous dimensions, and different bc cause a change in the ultraviolet asymptotic behavior of the self-energies, in this work we verify that it is possible to have a hard technifermion self-energy in TC models originated through radiative corrections coming from the interactions mediated by the new massive neutral and charged gauge bosons, $Z'$ and $U^{\pm\pm}$ in the context of a 331-TC model.

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arXiv2017

Anomalous mass dimensions and Schwinger-Dyson equations boundary condition

Theories with large mass anomalous dimensions ($γ_m$) have been extensively studied because of their deep consequences for models where the scalar bosons are composite. Large $γ_m$ values may appear when a non-Abelian gauge theory has a large number of fermions or is affected by four-fermion interactions. In this note we provide a simple explanation how $γ_m$ can be directly read out from the IR and UV boundary conditions derived from the gap equation, and verify that moderate $γ_m$ values appear when the theory possess a large number of fermions, but large $γ_m$ values are obtained only when four-fermion interactions are added to the theory. We also verify how the critical line separating the different chiral phases emerge from these conditions.

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arXiv2016

Anomalous mass dimension of multi-flavor QCD

Models of strongly interacting theories with a large mass anomalous dimension ($γ_m$) provide an interesting possibility for the dynamical origin of the electroweak symmetry breaking. A laboratory for these models is QCD with many flavors, which may present a non-trivial fixed point associated to a conformal region. Studies based on conformal field theories and on Schwinger-Dyson equations have suggested the existence of bounds on the mass anomalous dimension at the fixed points of these models. In this note we discuss $γ_m$ values of multi-flavor QCD exhibiting a non-trivial fixed point and affected by relevant four-fermion interactions.

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arXiv2016

Schwinger-Dyson approach and its application to generate a light composite scalar

We discuss the possibility of generating a light composite scalar boson, in a scenario that we may generically call Technicolor, or in any variation of a strongly interacting theory, where by light we mean a scalar composite mass about one order of magnitude below the characteristic scale of the strong theory. Instead of most of the studies about a composite Higgs boson, which are based on effective Lagrangians, we consider this problem in the framework of non-perturbative solutions of the fermionic Schwinger-Dyson and Bethe-Salpeter equations. We study a range of mechanisms proposed during the recent years to form such light composite boson, and verify that such possibility seems to be necessarily associated to a fermionic self-energy that decreases slowly with the momentum.

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arXiv2015

The Extreme Walking Behavior in a 331-TC Model

It is quite possible that the Technicolor problems are related to the poorly known self-energy expression, or the way chiral symmetry breaking (CSB) is realized in non-abelian gauge theories. Actually, the only known laboratory to test the CSB mechanism is QCD. The TC dynamics may be quite different from the QCD , this fact has led to the walking TC proposal making the new strong interaction almost conformal and changing appreciably its dynamical behavior. There are different ways to obtain of extreme walking (or quasi-conformal) technicolor theories, in this paper we propose an scheme to obtain this behavior based on an extension of the electroweak sector of the standard model, in the context of so called 331-TC model.

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arXiv2015

Composite Higgs Models, Technicolor and The Muon Anomalous Magnetic Moment

We revisit the muon magnetic moment (g-2) in the context of Composite Higgs models and Technicolor, and provide general analytical expressions for computing the muon magnetic moment stemming from new fields such as, neutral gauge bosons, charged gauge bosons, neutral scalar, charged scalars, and exotic charged leptons type of particles. Under general assumptions we assess which particle content could address the $g-2_μ$ excess. Moreover, we take a conservative approach and derive stringent limits on the particle masses in case the anomaly is otherwise resolved and comment on electroweak and collider bounds. Lastly, for concreteness we apply our results to a particular Technicolor model.

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arXiv2015

Light composite scalar boson from a see-saw mechanism in two-scale TC models

We consider the possibility of a light composite scalar boson arising from mass mixing between a relatively light and heavy scalar singlets in a see-saw mechanism expected to occur in two-scale Technicolor (TC) models. A light composite scalar boson can be generated when the TC theory features two technifermions species in different representations, $R_1$ and $R_2$, under a single technicolor gauge group, with characteristic scales $Λ_1$ and $Λ_2$. We determine the final composite scalar fields, $Φ_1$ and $Φ_2$, effective theory using the effective potential for composite operators approach. To generate a light composite scalar it is enough to have a walking (or quasi-conformal) behavior just for one of the technifermions representations.

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arXiv2015

QCD chiral symmetry restoration with a large number of quarks in a model with a confining propagator and dynamically massive gluons

Considering a QCD chiral symmetry breaking model where the gap equation contains an effective confining propagator and a dressed gluon propagator with a dynamically generated mass, we verify that the chiral symmetry is restored for a large number of quarks $n_{f}\approx 7-13$. We discuss the uncertainty in the results, that is related to the determination of the string tension ($K_{F}$), appearing in the confining propagator, and the effective gluon mass ($m_{g}$) at large $n_{f}$.

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arXiv2014

Chiral transition of fundamental and adjoint quarks

The chiral symmetry breaking transition of quarks in the fundamental and adjoint representation is studied in a model where the gap equation contains two contributions, one containing a confining propagator and another corresponding to the exchange of one-dressed dynamically massive gluons. When quarks are in the fundamental representation the confinement effect dominates the chiral symmetry breaking while the gluon exchange is suppressed due to the dynamical gluon mass effect in the propagator and coupling constant. In this case the chiral and deconfinement transition temperatures are approximately the same. For quarks in the adjoint representation, due to the larger Casimir eigenvalue, the gluon exchange is operative and the chiral transition happens at a larger temperature than the deconfinement one.

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arXiv2013

A 125 GeV Scalar Boson and SU(N_{TC})\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models

We verify that SU(N)_{{}_{TC}}\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models, where the gauge symmetry breaking is totally dynamical and promoted by the non-Abelian technicolor (TC) group and the strong Abelian interactions, are quite constrained by the LHC data. The theory contains a T quark self-energy involving the mixing between the neutral gauge bosons, which introduces the coupling between the light and heavy composite scalar bosons of the model. We determine the lightest scalar boson mass for these models from an effective action for composite operators, assuming details about the dynamics of the strong interaction theories. Comparing the value of this mass with the ATLAS and CMS observation of a new boson with a mass M_ϕ \sim 125GeV and considering the lower bound determined by the LHC Collaborations on the heavy neutral gauge boson (Z^\prime) present in these models, we can establish constraints on the possible models. For example, if SU(N)_{{}_{TC}}\equiv SU(2)_{{}_{TC}}, with technifermions in the fundamental representation, the model barely survives the confrontation with the LHC data.

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arXiv2012

How confinement may affect technicolor?

Confinement has been introduced into the quark gap equation, as proposed by Cornwall, as a possible solution to the problem of chiral symmetry breaking in QCD with dynamically massive gluons. We argue that the same mechanism can be applied for technicolor with dynamically massive technigluons. Within this approach both theories develop a hard self-energy dynamics, resulting from an effective four-fermion interaction, which does not lead to the known technicolor phenomenological problems. We outline a quite general type of technicolor model within this proposal that may naturally explain the masses of different fermion generations.

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arXiv2012

Dynamical Symmetry Breaking in a Minimal 3-3-1 Model

The gauge symmetry breaking in some versions of 3-3-1 models can be implemented dynamically because at the scale of a few TeVs the $U(1)_X$ coupling constant becomes strong. In this work we consider the dynamical symmetry breaking in a minimal $SU(3)_{{}_{TC}}\times SU(3)_{{}_{L}}\times U(1)_{X}$ model, where we propose a new scheme to cancel the chiral anomalies, including two-index symmetric (6) technifermions, which incorporates naturally the walking behavior in the TC sector. The composite scalar content of the model is minimal and all the symmetry breaking is implemented by a multiplet of technifermions. The choice of TC representations not only provide the anomaly cancellation with a walking behavior, but is crucial to promote the model's full dynamical symmetry breaking. We consider the dynamical generation of technigluon masses and, depending on the 3-3-1 symmetry breaking scale ($μ_{331}$), we verify that the technigluon mass is strongly linked to the $Z'$ mass scale, for instance, if $μ_{331}= 1TeV$, we have $M_{{}_{Z'}} > 1$ TeV only if $M_{{}_{TG}} < 350GeV$.

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arXiv2011

Chiral symmetry breaking in QCD-like gauge theories with a confining propagator and dynamical gauge boson mass generation

We study chiral symmetry breaking in QCD-like gauge theories introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamical gauge boson mass generation. The effective confining propagator has the form $1/(k^2+m^2)^2$ and we study the bifurcation equation finding limits on $m$ below which a satisfactory fermion mass solution is generated. Since the coupling constant and gauge boson propagator are damped in the infrared, due to the presence of dynamically massive gauge bosons, the major part of the chiral breaking is only due to the confining propagator. We study the asymptotic behavior of the gap equation containing confinement and massive gauge boson exchange, and find that the symmetry breaking can be approximated at some extent by an effective four-fermion interaction generated by the confining propagator. We compute some QCD chiral parameters as a function of $m$, finding values compatible with the experimental data. Within this approach we expect that lattice simulations should not see large differences between the confinement and chiral symmetry breaking scales independent of the fermionic representation and we find a simple approximate relation between the fermion condensate and dynamical mass for a given representation as a function of the parameters appearing in the effective confining propagator.

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arXiv2011

Chiral symmetry breaking with a confining propagator and dynamically massive gluons

Chiral symmetry breaking in QCD is studied introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamically massive gluons. The effective confining propagator has the form $1/(k^2+m^2)^2$ and we study the bifurcation equation finding limits on the parameter $m$ below which a satisfactory fermion mass solution is generated. Since the coupling constant and gluon propagator are damped in the infrared, due to the presence of a dynamical gluon mass, the major part of the chiral breaking is only due to the confining propagator and related to the low momentum region of the gap equation. We study the asymptotic behavior of the gap equation containing this confinement effect and massive gluon exchange, and find that the symmetry breaking can be approximated by an effective four-fermion interaction generated by the confining propagator. We compute some QCD chiral parameters as a function of $m$, finding values compatible with the experimental data. We find a simple approximate relation between the fermion condensate and dynamical mass for a given representation as a function of the parameters appearing in the effective confining propagator.

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arXiv2010

Vacuum energy as a c-function for theories with dynamically generated masses

We argue that in asymptotically free non-Abelian gauge theories possessing the phenomenon of dynamical mass generation the $β$ function is negative up to a value of the coupling constant that corresponds to a non-trivial fixed point, in agreement with recent AdS/QCD analysis. This fixed point happens at the minimum of the vacuum energy ($Ω$), which, as a characteristic of theories with dynamical mass generation, has the properties of a c-function.

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arXiv2010

The Gauge Bosons Masses in a SU(2)_TC x SU(3)_L x U(1)_X Extension of the Standard Model

The gauge symmetry breaking in 3-3-1 models can be implemented dynamically because at the scale of a few TeVs the U(1)_X coupling constant becomes strong. The exotic quark T introduced in the model will form a condensate breaking SU(3)_L x U(1)_X to electroweak symmetry. In this work we explore the full realization of the dynamical symmetry breaking of an 3-3-1 model to U(1)_{em} considering a model based on SU(2)_TC x SU(3)_L x U(1)_X. We compute the mass generated for the charged and neutral gauge bosons of the model that result from the symmetry breaking, and verify the equivalence between a 3-3-1 model with a scalar content formed by the set of the fundamental scalar bosons (chi), (rho) and (eta) with a 3-3-1 model where the dynamical symmetry breaking is implanted by the system formed by the set of composite bosons (Phi_T), (Phi_TC(1)) and (Phi_TC(2)). In this model the minimal composite scalar content is fixed by the condition of the cancellation of triangular anomaly in TC sector.

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arXiv2010

Deciphering the minimum of energy of some walking technicolor models

There are quasi-conformal theories, like the Minimal and Ultraminimal Technicolor models, which may break dynamically the gauge symmetry of the Standard Model and at the same time are compatible with electroweak precision data. The main characteristic of this type of models is their fermionic content in one or more higher dimensional representations, therefore it is not immediate to know which model leads to the most attractive channel or the minimum vacuum energy state. We discuss the effective potential for composite operators for these models, verifying that their vacuum energy values are different, with the Ultraminimal model having a deeper minimum of energy.

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