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R. Sekhar Chivukula

Publications and source records attributed to R. Sekhar Chivukula.

At least 127 records · Page 7Linked to original sources
arXiv1998

Large-N and Vacuum Alignment in Topcolor Models

Topcolor and topcolor-assisted technicolor provide examples of dynamical electroweak symmetry breaking which include top-condensation, thereby naturally incorporating a heavy top quark. In this note we discuss the roles of the Nambu-Jona-Lasinio (NJL) and large-N approximations often used in phenomenological analyses of these models. We show that, in order to provide for top-condensation but not bottom-condensation, the top-color coupling must be adjusted to equal the critical value for chiral symmetry breaking up to O(1/N) in any theory in which the isospin-violating ``tilting'' interaction is a U(1) gauge interaction. A consequence of these considerations is that the potentially dangerous ``bottom-pions'' are naturally light. We also show that the contributions to rho-1 previously estimated are of leading-order in N, are not included in the usual NJL analysis, and are the result of ``vacuum-alignment''.

hep-ph↗
arXiv1998

Models of Electroweak Symmetry Breaking

Discovering the dynamics responsible for electroweak symmetry breaking is the outstanding question facing particle physics today, and the answer will be found in the next decade. In these lectures I discuss the range of models which have been proposed to explain electroweak symmetry breaking. I begin with an overview of Higgs models, with emphasis on the naturalness/hierarchy and triviality problems, and then consider general lessons which can be drawn about the symmetry breaking sector in arbitrary scalar models. Subsequently, I discuss the symmetry breaking sector in supersymmetric models and then consider models of dynamical electroweak symmetry breaking. I conclude with a brief review of the open questions.

hep-ph↗
arXiv1996

A Comment on the Zero Temperature Chiral Phase Transition in $SU(N)$ Gauge Theories

Recently Appelquist, Terning, and Wijewardhana investigated the zero temperature chiral phase transition in SU(N) gauge theory as the number of fermions N_f is varied. They argued that there is a critical number of fermions N^c_f, above which there is no chiral symmetry breaking and below which chiral symmetry breaking and confinement set in. They further argued that that the transition is not second order even though the order parameter for chiral symmetry breaking vanishes continuously as N_f approaches N^c_f on the broken side. In this note I propose a simple physical picture for the spectrum of states as N_f approaches N^c_f from below (i.e. on the broken side) and argue that this picture predicts very different and non-universal behavior than is the case in an ordinary second order phase transition. In this way the transition can be continuous without behaving conventionally. I further argue that this feature results from the (presumed) existence of an infrared Banks-Zaks fixed point of the gauge coupling in the neighborhood of the chiral transition and therefore depends on the long-distance nature of the non-abelian gauge force.

hep-ph↗
arXiv1995

Strong W_L W_L Scattering

I describe theories of a strongly-interacting electroweak symmetry breaking sector and discuss the expected size of anomalous weak-boson couplings in these models.

hep-ph↗
arXiv1995

Strongly Coupled Electroweak Symmetry Breaking: Implications of Models

We discuss the phenomenology of models of dynamical electroweak symmetry breaking which attempt to generate the observed fermion mass spectrum. After briefly describing the variety of and constraints on proposed models, we concentrate on the signatures of colored pseudo-Nambu-Goldstone bosons and resonances at existing and proposed colliders. These particles provide a possibly unique signature: strongly produced resonances associated with electroweak symmetry breaking. (This is the subgroup report for the ``Electroweak Symmetry Breaking and Beyond the Standard Model" working group of the DPF Long Range Planning Study. This report will appear as a chapter in ``Electroweak Symmetry Breaking and Beyond the Standard Model", edited by T. Barklow, S. Dawson, H.E. Haber, and J. Siegrist, to be published by World Scientific.)

hep-ph↗
arXiv1994

The Higgs Boson Width is Adjustable

We show that it is possible to construct models in which the width of the Higgs boson is arbitrary - either smaller or larger than a standard model Higgs boson of the same mass. There are no new fields into which the Higgs boson decays. Instead, the coupling of the Higgs boson to the gauge bosons is adjusted. We construct and analyze weakly--coupled models with arbitrary--width Higgs bosons to investigate the phenomenology one might find in a strongly interacting model. In any such model new physics must enter at a mass scale which decreases as the Higgs boson width is adjusted away from its standard model value. In particular, if the Higgs boson is wider than the standard model Higgs boson, then interesting new physics must appear in the isospin--two channel.

hep-ph↗
arXiv1994

When is a Higgs THE Higgs?

The one-Higgs-doublet standard model is necessarily incomplete because of the triviality of the scalar symmetry-breaking sector. If the Higgs mass is approximately 600 GeV or higher, there must be additional dynamics at a scale $Λ$ which is less than a few TeV. In this case the properties of the Higgs resonance can differ substantially from those predicted by the standard model. In this talk we construct an effective Lagrangian description of a theory with a non-standard Higgs boson and analyze the features of a theory with such a resonance coupled to the Goldstone Bosons of the breaking of $\su$.

hep-ph↗
arXiv1994

The Phenomenology of a Non-Standard Higgs Boson IN $W_{L}W_{L}$ Scattering

In this paper we consider the phenomenology of a ``non-standard'' Higgs Boson in longitudinal gauge-Boson scattering. First, we present a composite Higgs model (based on an $SU(4)/Sp\,(4)$ chiral-symmetry breaking pattern) in which there is a non-standard Higgs Boson. Then we explore, in a model-independent way, the phenomenology of such a non-standard Higgs by calculating the chiral logarithmic corrections to longitudinal gauge scattering. This calculation is done using the Equivalence theorem and the Higgs is treated as a scalar-isoscalar resonance coupled to the Goldstone Bosons of the \mbox{$SU(2)_{L} \times SU(2)_{R}/SU(2)_{V}$} chiral symmetry breaking. We show that the most important deviation from the one Higgs-doublet standard model is parameterized by one unknown coefficient which is related to the Higgs width. The implications for future hadron colliders are discussed.

hep-ph↗
arXiv1993

Phenomenology of a Non-Standard Higgs

The one-Higgs-doublet standard model is necessarily incomplete because of the triviality of the scalar symmetry-breaking sector. If the Higgs mass is approximately 600 GeV or higher, there must be additional dynamics at a scale $Λ$ which is less than a few TeV. In this case the properties of the Higgs resonance can differ substantially from those predicted by the standard model. In this letter we construct an effective Lagrangian description of a theory with a non-standard Higgs boson and analyze the features of a theory with such a resonance coupled to the Goldstone Bosons of the breaking of $\su$. This Lagrangian describes the most general theory in which the Higgs and the Goldstone Bosons are the only particles with a mass small compared to $Λ$. We compute the leading corrections to the decay width of the Higgs boson and the contribution to the Peskin-Takeuchi parameter $S$ and present results for the corrections to Goldstone Boson scattering. We find that the most prominent effects are due to one new parameter, which is directly related to the Higgs boson width.

hep-ph↗
arXiv1993

Triviality Bounds in Two-Doublet Models

We examine perturbatively the two-Higgs-doublet extension of the \SM\ in the context of the suspected triviality of theories with fundamental scalars. Requiring the model to define a consistent effective theory for scales below a cutoff of $2π$ times the largest mass of the problem, as motivated by lattice investigations of the one-Higgs-doublet model, we obtain combined bounds for the parameters of the model. We find upper limits of 470 GeV for the mass of the light $CP$--even neutral scalar and 650--700 GeV for the other scalar masses.

hep-ph↗
arXiv1992

Critical Constraints on Chiral Hierarchies

We consider the constraints that critical dynamics places on models with a top quark condensate or strong extended technicolor (ETC). These models require that chiral-symmetry-breaking dynamics at a high energy scale plays a significant role in electroweak symmetry breaking. In order for there to be a large hierarchy between the scale of the high energy dynamics and the weak scale, the high energy theory must have a second order chiral phase transition. If the transition is second order, then close to the transition the theory may be described in terms of a low-energy effective Lagrangian with composite ``Higgs'' scalars. However, scalar theories in which there are more than one $Φ^4$ coupling can have a {\it first order} phase transition instead, due to the Coleman-Weinberg instability. Therefore, top-condensate or strong ETC theories in which the composite scalars have more than one $Φ^4$ coupling cannot always support a large hierarchy. In particular, if the Nambu--Jona-Lasinio model solved in the large-$N_c$ limit is a good approximation to the high-energy dynamics, then these models will not produce acceptable electroweak symmetry breaking.

hep-ph↗
arXiv1992

A Comment on the Strong Interactions of Color-Neutral Technibaryons

We estimate the cross section for the scattering of a slow, color-neutral technibaryon made of colored constituents with nuclei. We find a cross section of order $A^2\ 10^{-45}$ cm$^2$, where $A$ is the atomic number of the nucleus. Even if technibaryons constitute the dark matter in the galactic halo, this is too small to be detected in future underground detectors.

hep-ph↗
arXiv1992

The Phenomenology of a Hidden Symmetry Breaking Sector

We calculate the production rate of gauge-boson pairs at the SSC in a model with a ``hidden'' electroweak symmetry breaking sector. We show that the signal of electroweak symmetry breaking is lower than the background and that we cannot necessarily rely on gauge boson pairs as a signal of the dynamics of symmetry breaking.

hep-ph↗