R. D. Peccei

The Strong CP Problem and Axions

I describe how the QCD vacuum structure, necessary to resolve the U(1)_A problem, predicts the presence of a PabbrevPparity transformation, TabbrevTtime reversal transformation, and CPabbrevCPcharge conjugation transformation followed by party transformation violating term proportional to the vacuum angle θ. To agree with experimental bounds, however, this parameter must be very small (θ < 10-9). After briefly discussing some other possible solutions to this, so-called, strong CP problem, I concentrate on the chiral solution proposed by Peccei and Quinn which has associated with it a light pseudoscalar particle, the axion. I discuss in detail the properties and dynamics of axions, focusing particularly on invisible axion models where axions are very light, very weakly coupled, and very long-lived. Astrophysical and cosmological bounds on invisible axions are also briefly touched upon.

Remarks on nonperturbativeO(1/mc2)corrections toΓ(B¯→Xsγ)

We present an estimate of certain higher order corrections to the contribution of the charm triangle loop in the inclusive B -> X_s gamma decay rate, recently discussed by Voloshin. We find that these corrections are minute and hence the result found by Voloshin, although small, is quite robust.

Natural mass matrices

We introduce the idea of natural mass matrices, an organizing principle useful in the search for GUT scale quark mass matrix patterns that are consistent with known CKM constraints and quark mass eigenvalues. An application of this idea is made in the context of SUSY GUT{close_quote}s and some potentially {open_quote}{open_quote}successful{close_quote}{close_quote} GUT scale mass patterns are found. The CKM predictions of these patterns are presented and some relevant strong {ital CP} issues are discussed. {copyright} {ital 1996 The American Physical Society.}

Reflections on the strong CP problem

Abstract I discuss how anomalies affect classical symmetries and how, in turn, the non-trivial nature of the gauge theory vacuum makes these quantum corrections troublesome. Although no solution seems in sight for the cosmological constant problem, I examine three possible approaches to the strong CP problem involving vacuum dynamics, an additional chiral symmetry, and the possibility of spontaneous CP or P breaking. All of these “solutions” have their own problems and suggest that, at a deep level, we do not understand the nature of CP violation. Nevertheless, it remains extremely important to search for experimental signals predicted by these theoretical “solutions”, like invisible axions.

Can supersymmetry breaking lead to electroweak symmetry breaking via formation of scalar bound states

Abstract The recent discovery of the putative 125 GeV Higgs boson has motivated a number of attempts to reconcile its relatively large mass with the predictions of the minimal supersymmetric standard model (MSSM). Some approaches invoked large trilinear supersymmetry breaking terms A t between stops and one of the elementary Higgs fields. We consider the possibility that electroweak symmetry breaking may be triggered by supersymmetry breaking with a large A t , large enough to generate a composite field with the same quantum numbers as the Higgs boson and with a non-vanishing vacuum expectation value. In the resulting vacuum, the usual relation between the gauge couplings and the Higgs self-coupling does not apply, and there is no reason to expect the same upper bound on the mass of the lightest Higgs boson. In a simple model where the bound state is assumed to have no mixing with the other fields, we calculate the critical coupling A t necessary for symmetry breaking using the lowest-order Bethe–Salpeter (BS) equation. Study of the BS equation is complicated by the structure of its lowest-order kernel, which is a crossed box graph, but we find an accurate approximation to its solution. In a realistic model, the mixing of the bound state with the fundamental Higgs boson creates a symmetry-breaking seesaw. We outline the steps toward a realistic model.

Discrete and global symmetries in particle physics

I begin these lectures by examining the transformation properties of quantum fields under the discrete symmetries of Parity, P, Charge Conjugation, C, and Time Reversal, T. With these results in hand, I then show how the structure of the Standard Model helps explain the conservation/violation of these symmetries in various sectors of the theory. This discussion is also used to give a qualitative proof of the CPT Theorem, and some of the stringent tests of this theorem in the neutral Kaon sector are reviewed. In the second part of these lectures, global symmetries are examined. Here, after the distinction between Wigner-Weyl and Nambu-Goldstone realizations of these symmetries is explained, a discussion is given of the various, approximate or real, global symmetries of the Standard Model. Particular attention is paid to the role that chiral anomalies play in altering the classical symmetry patterns of the Standard Model. To understand the differences between anomaly effects in QCD and those in the electroweak theory, a discussion of the nature of the vacuum structure of gauge theories is presented. This naturally raises the issue of the strong CP problem, and I present a brief discussion of the chiral solution to this problem and of its ramifications for astrophysics and cosmology. I also touch briefly on possible constraints on, and prospects for, having real Nambu-Goldstone bosons in nature, concentrating specifically on the simplest example of Majorons. I end these lectures by discussing the compatibility of having global symmetry in the presence of gravitational interactions. Although these interactions, in general, produces small corrections, they can alter significantly the Nambu-Goldstone sector of theories.

Light Scalars in Cosmology

I discuss here some of the constraints imposed by quantum and gravitational corrections on two hypothetical excitations, axions and quintessence, which have important cosmological implications. Although these corrections can be kept under control, the resulting constraints are not too natural. In particular, to keep the quintessence field light one must essentially decouple it from ordinary matter. Some possible suggestions of how to avoid these troubles are briefly touched upon.

Phenomenology of supersymmetric models with a symmetry-breaking seesaw mechanism

We explore phenomenological implications of the minimal supersymmetric standard model (MSSM) with a strong supersymmetry breaking trilinear term. Supersymmetry breaking can trigger electroweak symmetry breaking via a symmetry-breaking seesaw mechanism, which can lead to a low-energy theory with multiple composite Higgs bosons. In this model, the electroweak phase transition can be first-order for some generic values of parameters. Furthermore, there are additional sources of CP violation in the Higgs sector. This opens the possibility of electroweak baryogenesis in the strongly coupled MSSM. The extended Higgs dynamics can be discovered at Large Hadron Collider or at a future linear collider.

Comment On Nonperturbative O(1/m_c^2) Corrections to B -> X_s gamma

We present an estimate of certain higher order corrections to the contribution of the charm triangle loop in the inclusive B -> X_s gamma decay rate, recently discussed by Voloshin. We find that these corrections are minute and hence the result found by Voloshin, although small, is quite robust.

Speculations on ALEPH's dijet enhancement

Abstract We interpret the dijet enhancement reported by the ALEPH collaboration in the process e + e − →4 jets as being due to the production of a pair of bottom squarks, followed by their R-parity violating decays into pairs of light quarks. Constraints on this speculative interpretation are examined. Some of the consequences of our hypothesis are drawn within the context of softly broken supersymmetry.