Strong Gauge Interaction Research Articles

Reviving sub-TeV SU(2)_L lepton doublet dark matter

In this work we study the hybrid kind of dark matter (DM) production mechanism where both thermal and non-thermal contribution at two different epochs set the DM relic abundance. This hybrid set up in turn shifts the parameter space of DM in contrast to pure thermal DM scenario. We review such production mechanism in the context of the SU(2)_L lepton doublet dark matter (Psi ) augmented with an additional singlet dark scalar (S). The neutral component of the dark doublet can serve as a stable DM candidate and in pure thermal scenario, it is under-abundant as well as excluded from direct detection constraints due to its strong gauge interactions in the sub-TeV mass regime. However, in addition to the thermal contribution, the late time non-thermal DM production from the decay of the long-lived dark scalar S helps to fulfill the deficit in DM abundance. On the other hand, the strong gauge mediated direct detection constraint can be evaded with the help of a SU(2)_L triplet scalar(with Y=2), resulting a pseudo-Dirac DM. To realize our proposed scenario we impose a discrete {mathcal {Z}}_2 symmetry under which both Psi and S are odd while rest of the fields are even. We find the lepton doublet pseudo-Dirac DM with mass sim 450{-}1200 GeV, compatible with the observed relic density, direct, indirect, and existing collider search constraints.

Holographic Kondo and Fano resonances

We use holography to study a $(1+1)$-dimensional Conformal Field Theory (CFT) coupled to an impurity. The CFT is an $SU(N)$ gauge theory at large $N$, with strong gauge interactions. The impurity is an $SU(N)$ spin. We trigger an impurity Renormalization Group (RG) flow via a Kondo coupling. The Kondo effect occurs only below the critical temperature of a large-$N$ mean-field transition. We show that at all temperatures $T$, impurity spectral functions exhibit a Fano resonance, which in the low-$T$ phase is a large-$N$ manifestation of the Kondo resonance. We thus provide an example in which the Kondo resonance survives strong correlations, and uncover a novel mechanism for generating Fano resonances, via RG flows between $(0 + 1)$-dimensional fixed points

Dynamical generation of the weak and Dark Matter scales from strong interactions

Assuming that mass scales arise in nature only via dimensional transmutation, we extend the dimension-less Standard Model by adding vector-like fermions charged under a new strong gauge interaction. Their non-perturbative dynamics generates a mass scale that is transmitted to the elementary Higgs boson by electro-weak gauge interactions. In its minimal version the model has the same number of parameters as the Standard Model, predicts that the electro-weak symmetry gets broken, predicts new-physics in the multi-TeV region and is compatible with all existing bounds, provides two Dark Matter candidates stable thanks to accidental symmetries: a composite scalar in the adjoint of SU(2)_L and a composite singlet fermion; their thermal relic abundance is predicted to be comparable to the measured cosmological DM abundance. Some models of this type allow for extra Yukawa couplings; DM candidates remain even if explicit masses are added.

DYNAMICAL ELECTROWEAK SYMMETRY BREAKING IN STRING MODELS WITH D-BRANES

The possibility of dynamical electroweak symmetry breaking by strong coupling gauge interaction in models with D-branes in String Theory is examined. Instead of elementary scalar Higgs doublet fields, the gauge symmetry with strong coupling (technicolor) is introduced. As the first step of this direction, a toy model, which is not fully realistic, is concretely analyzed in some detail. The model consists of D-branes and anti-D-branes at orbifold singularities in (T2 × T2 × T2)/Z3 which preserves supersymmetry. Supersymmetry is broken through the brane supersymmetry breaking. It is pointed out that the problem of large S parameter in dynamical electroweak symmetry breaking scenario may be solved by natural existence of kinetic term mixings between hypercharge U(1) gauge boson and massive anomalous U(1) gauge bosons. The problems to be solved toward constructing more realistic models are clarified in the analysis.

Searching for composite neutrinos in the cosmic microwave background

We analyze signals in the Cosmic Microwave Background (CMB) in theories where the small Dirac neutrino masses arise as a consequence of the compositeness of right-handed neutrinos. In such theories, the right-handed neutrinos are massless ``baryons'' of a new strong gauge interaction. We find that the results crucially depend on whether or not the new strong sector undergoes chiral symmetry breaking. In the case with chiral symmetry breaking, we find that there are indeed signals in the CMB, but none of them is a direct consequence of neutrino compositeness. In contrast, if the underlying theory does not undergo chiral symmetry breaking, the large scattering cross-section among the composites gives rise to a sizable CMB signal over a wide region of the parameter space, and it can potentially probe whether the neutrino mass spectrum is hierarchical, inverse hierarchical, or degenerate. We also discuss collider constraints on the compositeness in the context of the CMB signals.

MINIMAL ELECTROWEAK SYMMETRY BREAKING MODEL IN EXTRA DIMENSIONS

We show that if the Standard Model gauge fields and fermions propagate in extra dimenions, a composite Higgs field with the correct quantum number can arise naturally as a bound state due to the strong gauge interactions in higher dimensions. The top quark mass and the Higgs mass can be predicted from the infrared fixed points of the renormalization group equations. The top quark mass is in good agreement with the experimental value, and the Higgs boson mass is predicted to be ~ 200GeV. There may be some other light bound states which could be observed at upcoming collider experiments.

Dynamical doublet-triplet Higgs boson mass splitting

We propose a new mechanism towards the solution to the doublet-triplet Higgs mass splitting problem in the supersymmetric grand unified theory. Our model is based on the gauge group $SU(5)_H \times SU(5)_{GUT}$, where $SU(5)_H$ and $SU(5)_{GUT}$ are a new strong gauge interaction and the ordinary grand unified gauge group, respectively. The doublet-triplet Higgs mass splitting is realized through the quantum deformation of moduli space caused by the strong $SU(5)_H$ gauge dynamics. The low energy description of our model is given by the minimal supersymmetric standard model.

MASS GENERATION AND THE DYNAMICAL ROLE OF THE KATOPTRON GROUP

Heavy mirror fermions along with a new strong gauge interaction capable of breaking the electroweak gauge symmetry dynamically were recently introduced under the name of katoptrons. Their main function is to provide a viable alternative to the Standard-Model Higgs sector. In such a framework, ordinary fermions acquire masses after the breaking of the strong katoptron group which allows mixing with their katoptron partners. The purpose of this letter is to study the elementary-scalars-free mechanism responsible for this breaking and its implications for the fermion mass hierarchies.

Analysis of the Wilsonian effective potentials in dynamical chiral symmetry breaking

The nonperturbative renormalization group equation for the Wilsonian effective potential is given in a certain simple approximation scheme in order to study chiral symmetry breaking phenomena dynamically induced by strong gauge interactions. The evolving effective potential is found to be nonanalytic in the infrared, which indicates spontaneous generation of the fermion mass. It is also shown that the renormalization group equation gives the identical effective fermion mass with that obtained by solving the Schwinger-Dyson equation in the (improved) ladder approximation. Moreover, the introduction of the collective field corresponding to the fermion composite into the theory space is found to offer an efficient method to evaluate the order parameters: the dynamical mass and the chiral condensate. The relation between the renormalization group equation incorporating the collective field and the Schwinger-Dyson equation is also clarified.

New axial interactions at 1 TeV

We consider a heavy fourth family with masses lying in the symmetry breaking channel of a new strong gauge interaction. This interaction generates a heavy quark axial-type operator, whose effects can be enhanced through multiple insertions. In terms of the strength of this operator we can express new negative contributions to the S and T parameters and the shifts of the Z couplings to the third family. In particular we find that the new contribution to T is strongly constrained by the experimental constraints on the Z coupling to the \ensuremath{\tau}.

Dynamical fermion mass generation at a tricritical point in strongly coupled U(1) lattice gauge theory

Fermion mass generation in the strongly coupled U(1) lattice gauge theory with fermion and scalar fields of equal charge is investigated by means of numerical simulation with dynamical fermions. The chiral symmetry of this model is broken by the gauge interaction and restored by the light scalar. We present evidence for the existence of a particular, tricritical point of the corresponding phase boundary where the continuum limit might possibly be constructed. It is of interest as a model for dynamical symmetry breaking and mass generation due to a strong gauge interaction. In addition to the massive and unconfined fermion $F$ and Goldstone boson $\ensuremath{\pi},$ a gauge ball of mass ${m}_{S}\ensuremath{\simeq}{1/2m}_{F},$ and some other states are found. The tricritical exponents appear to be nonclassical.

Influence of a new strong gauge interaction on unification

We investigate the influence of a new strong gauge interaction on the behavior of the running couplings of the standard model. The effects are parametrized to all orders in the new strong interactions and to next-to-leading order in the standard model couplings. We consider the unification of couplings in the presence of new fermions, which may or may not come in complete families. In the former case, a gauged family symmetry has very little impact on the question of unification.

Glueballs in strongly interacting theories at the electroweak scale

Several proposals for dynamical electroweak symmetry breaking and fermion mass generation involve strong gauge interactions with a characteristic scale of a few hundred GeV. The detection of the glueballs which should occur in such models would be a indication of the non-Abelian nature of the gauge theories operating at this scale. We discuss signatures for these particles.

Dynamical fermion mass generation by strong gauge interaction shielded by a scalar field.

The strongly coupled lattice gauge models with confined fermion and scalar matter fields, which in a certain phase break dynamically a global chiral symmetry, are reconsidered from the point of view of the existence of heavy fermions. In these models heavy fermions can arise as neutral bound states of the fundamental fermion and scalar. We call this mechanism of dynamical fermion mass generation the shielded gauge mechanism. The scalar field induces at strong gauge coupling a second order phase transition which is necessary for a continuum limit. Therefore the mechanism might well exist also in continuum. In this case, assuming that strongly coupled chiral gauge theories with scalars have similar dynamical properties at strong coupling as the vectorlike models investigated on the lattice, the discussed mechanism could be considered as an alternative to the Higgs mechanism. In particular, if the broken global chiral symmetry is SU(2) and the heavy fermion interpreted as a top quark, the mechanism is analogous to some gauge models for the top quark condensate. We present some numerical data obtained in the quenched approximation of a model with vectorlike U(1) gauge symmetry. The observed scaling behavior of the chiral condensate and of the fermion mass and also the properties of Goldstone bosons are the first encouraging steps in a study of the continuum limit of the mechanism.

Generalized dimensional analysis

I give a simple qualitative derivation and interpretation of a generalization of so-called naive dimensional analysis, a rule for estimating the sizes of terms in an effective theory below the scale of chiral symmetry breaking induced by a strong gauge interaction. The generalization includes the well known N c dependence of ƒ π as a special case but I suggest that it also applies to situation very unlike QCD.

Composite-technicolor standard model

We characterize a class of composite models in which the quarks and leptons and technifermions are built from fermions (preons) bound by strong gauge interactions. We argue that if the preon dynamics has as [SU(3) × U(1)] 5 flavor symmetry that is explicitly broken only by preon mass terms proportional to the quark and lepton mass matrices, then the composite-tech-nicolor theory has a GIM mechanism that suppresses dangerous flavor changing neutral current effects. We show that the compositeness scale must be between ≈1 TeV and ≈2.5 TeV, giving rise to observable deviations from the standard electroweak interactions, and that B B mixing and CP violation in K mesons can differ significantly from the standard model predictions. The lepton flavor symmetries may be observable in the near future in the comparison of the compositeness effects in e +e − → μ +μ − with those in e +e − → e +e −.

A tool kit for builders of composite models

I motivate and discuss a dynamical picture of strong gauge interactions in a simple class of models, some of which yield massless composite fermions. I show how to put simple components together into models that can describe quarks with color and flavor.

Trace and dilatation anomalies in gauge theories

The form of the anomaly in the trace of the energy-momentum tensor in a general theory of interacting fermions and non-Abelian gauge bosons is dervied. The result is shown to involve precisely those gaugevariant operatos which are known to mix with the naive trace under renormalization. The trace is shown to be soft on the mass shell if and only if the theory is at an eigenvalue of the Callan-Symanzik $\ensuremath{\beta}$ function. The dilatation anomaly in the matrix element of $\ensuremath{\theta}_{}^{\ensuremath{\lambda}}{}_{\ensuremath{\lambda}}{}^{}$ with two electromagnetic currents (to lowest order in electromagnetism, but including all orders of the strong gauge interaction) is derived and shown to be infinitely renormalized in finite orders of strong perturbation theory. This anomaly is then shown to be canonical and given precisely by the lowest-order result provided the strong interactions are summed to all orders before going to the limit of physical space-time dimensions.