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A. G. Cohen

Publications and source records attributed to A. G. Cohen.

11 recordsLinked to original sources
arXiv2002

The Littlest Higgs

We present an economical theory of natural electroweak symmetry breaking, generalizing an approach based on deconstruction. This theory is the smallest extension of the Standard Model to date that stabilizes the electroweak scale with a naturally light Higgs and weakly coupled new physics at TeV energies. The Higgs is one of a set of pseudo Goldstone bosons in an $SU(5)/SO(5)$ nonlinear sigma model. The symmetry breaking scale $f$ is around a TeV, with the cutoff $Λ\lsim 4πf \sim $ 10 TeV. A single electroweak doublet, the ``little Higgs'', is automatically much lighter than the other pseudo Goldstone bosons. The quartic self-coupling for the little Higgs is generated by the gauge and Yukawa interactions with a natural size $O(g^2,λ_t^2)$, while the top Yukawa coupling generates a negative mass squared triggering electroweak symmetry breaking. Beneath the TeV scale the effective theory is simply the minimal Standard Model. The new particle content at TeV energies consists of one set of spin one bosons with the same quantum numbers as the electroweak gauge bosons, an electroweak singlet quark with charge 2/3, and an electroweak triplet scalar. One loop quadratically divergent corrections to the Higgs mass are cancelled by interactions with these additional particles.

hep-ph↗
arXiv2002

The Minimal Moose for a Little Higgs

Recently a new class of theories of electroweak symmetry breaking have been constructed. These models, based on deconstruction and the physics of theory space, provide the first alternative to weak-scale supersymmetry with naturally light Higgs fields and perturbative new physics at the TeV scale. The Higgs is light because it is a pseudo-Goldstone boson, and the quadratically divergent contributions to the Higgs mass are cancelled by new TeV scale ``partners'' of the {\em same} statistics. In this paper we present the minimal theory space model of electroweak symmetry breaking, with two sites and four link fields, and the minimal set of fermions. There are very few parameters and degrees of freedom beyond the Standard Model. Below a TeV, we have the Standard Model with two light Higgs doublets, and an additional complex scalar weak triplet and singlet. At the TeV scale, the new particles that cancel the 1-loop quadratic divergences in the Higgs mass are revealed. The entire Higgs potential needed for electroweak symmetry breaking--the quartic couplings as well as the familiar negative mass squared--can be generated by the top Yukawa coupling, providing a novel link between the physics of flavor and electroweak symmetry breaking.

hep-ph↗
arXiv1999

Tunneling of Bound Systems at Finite Energies: Complex Paths Through Potential Barriers

We adapt the semiclassical technique, as used in the context of instanton transitions in quantum field theory, to the description of tunneling transmissions at finite energies through potential barriers by complex quantum mechanical systems. Even for systems initially in their ground state, not generally describable in semiclassical terms, the transmission probability has a semiclassical (exponential) form. The calculation of the tunneling exponent uses analytic continuation of degrees of freedom into a complex phase space as well as analytic continuation of the classical equations of motion into the complex time plane. We test this semiclassical technique by comparing its results with those of a computational investigation of the full quantum mechanical system, finding excellent agreement.

quant-ph↗
arXiv1999

The Semiclassical Description of Tunneling in Scattering with Multiple Degrees of Freedom

We describe a computational investigation of tunneling at finite energy in a weakly coupled quantum mechanical system with two degrees of freedom. We compare a full quantum mechanical analysis to the results obtained by making use of a semiclassical technique developed in the context of instanton-like transitions in quantum field theory. This latter technique is based on an analytic continuation of the degrees of freedom into a complex phase space, and the simultaneous analytic continuation of the equations of motion into the complex time plane.

hep-ph↗
arXiv1997

A Matter-Antimatter Universe?

We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. We demonstrate that, after recombination, it is impossible to avoid annihilation near regional boundaries. We study the dynamics of this process to estimate two of its signatures: a contribution to the cosmic diffuse gamma-ray background and a distortion of the cosmic microwave background. The former signal exceeds observational limits unless the matter domain we inhabit is virtually the entire visible universe. On general grounds, we conclude that a matter-antimatter symmetric universe is empirically excluded.

astro-ph↗
arXiv1997

Scars on the CBR?

We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. In previous work we demonstrated that post-recombination matter-antimatter contact near regional boundaries leads to an observable (but unobserved) gamma-ray flux for domain sizes of less than a few thousand Mpc, thereby excluding such domains. In this paper we consider the pre-recombination signal from domains of larger size.

astro-ph↗
arXiv1996

The More Minimal Supersymmetric Standard Model

Effective Supersymmetry is presented as a theory of physics above the electroweak scale which has significant theoretical advantages over both the standard model and the Minimal Supersymmetric Standard Model (MSSM). The theory is supersymmetric at short distances but differs significantly from the MSSM. Flavor symmetry violation is intimately related to supersymmetry breaking. There is a new physics scale $\mt\sim$~5--20 TeV which sets the mass of the first two sparticle families. Supersymmetric sources of CP violation and flavor changing neutral currents for the first two families are suppressed. Effective Supersymmetry can be implemented with automatic suppression of baryon and lepton number violation and a dynamically generated $μ$ term, while maintaining naturalness in the Higgs sector. There are implications for new particle searches, flavor and CP violation experiments, as well as for the construction of theories of flavor and dynamical supersymmetry breaking.

hep-ph↗
arXiv1996

New Strong Interactons at the Tevatron ?

Recent results from CDF indicate that the inclusive cross section for jets with $E_T > 200$ GeV is significantly higher than that predicted by QCD. We describe here a simple flavor-universal variant of the ``coloron" model of Hill and Parke that can accommodate such a jet excess, and which is not in contradiction with other experimental data. As such, the model serves as a useful baseline with which to compare both the data and other models proposed to describe the jet excess. An interesting theoretical feature of the model is that if the global chiral symmetries of the quarks remain unbroken in the confining phase of the coloron interaction, it realizes the possibility that the ordinary quarks are composite particles.

hep-ph↗
arXiv1994

Diffusion Enhances Spontaneous Electroweak Baryogenesis

We include the effects of diffusion in the electroweak spontaneous baryogenesis scenario and show that it can greatly enhance the resultant baryon density, by as much as a factor of $1/α_w^4 \sim 10^6$ over previous estimates. Furthermore, the baryon density produced is rather insensitive to parameters characterizing the first order weak phase transition, such as the width and propagation velocity of the phase boundary.

hep-ph↗
arXiv1992

Debye Screening and Baryogenesis during the Electroweak Phase Transition

We examine a recent claim that Debye screening will affect the charge transport mechanism of anomalous electroweak baryogenesis. We show that the effects of gauge charge screening do not affect the baryon number produced during a first order electroweak phase transition. (Requires harvmac.tex)

hep-ph↗