Herbert K. Dreiner

An Introduction to explicit R-parity violation

Until recently, R-parity violation (6 Rp) has been considered an unlikely component of the supersymmetric extension of the Standard Model (SM). In the past two years, it has motivated potentially favoured solutions to experimentally observed discrepancies (e.g. Rb, Rc, ALEPH four-jet events, HERA high Q excess). It is the purpose of this chapter to present 6 Rp as an equally well motivated supersymmetric extension of the SM and provide an introductory guide. I start out with the definition of Rp and the most serious problem of proton decay. Then I discuss the various motivations for 6 Rp, contrasting them with the Rp-conserving MSSM. Afterwards, I give an overview of the phenomenology of 6 Rp. I finish with a discussion on cosmological effects.

Bounds on R -parity violating couplings at the weak scale and at the GUT scale

We analyse bounds on trilinear R-parity violating couplings at the unification scale by renormalising the weak scale bounds. We derive unification scale upper bounds upon the couplings which are broadly independent of the fermion mass texture assumed. The R-parity violating couplings are factors of two to five more severely bounded at the unification scale than at the electroweak scale. In the presence of quark mixing, a few of the bounds are orders of magnitude stronger than their weak scale counterparts due to new R-parity violating operators being induced in the renormalisation between high and low scales. These induced bounds are fermion mass texture dependent. New bounds upon the weak scale couplings are obtained by the requirement of perturbativity between the weak and unification scales. A comprehensive set of the latest limits is included.

Sphaleron erasure of primordial baryogenesis

Abstract If the present baryon asymmetry is due to a Planck or GUT-scale matter asymmetry then baryon- or lepton-number violating processes are constrained by the condition that they do not subsequently erase this asymmetry. We present a revision of the analysis of sphaleron baryon-number violating processes in the standard model including lepton-mass effects. We find the surprising result that a GUT-scale matter asymmetry can survive the B and L violating sphaleron interactions even though ( B - L ) is conserved and equals zero for all temperatures. We extend the analysis to cover the minimal supersymmetric standard model (MSSM) and also derive the constraints on the R -parity violating couplings in extensions of the MSSM. In the case of the baryon number violating dimension 4 operators we find, contrary to current wisdom, that the resulting bounds can be avoided completely because of a residual lepton-flavour number conservation; in the case of lepton number violating operators we find the bounds are flavour dependent and can be avoided completely in definite flavour channels. We also consider how the bounds are modified in the case where there is a Grand Unified extension of the supersymmetric model which introduces new lepton flavour violating couplings.

Correlation of B(s) --> mu(+)mu(-) and (g - 2)(mu) in minimal supergravity.

We analyze the decay mode B(s)-->mu(+)mu(-) in minimal supergravity (mSUGRA). We find that the recently measured excess in (g-2)(mu), if interpreted within mSUGRA, is correlated with a substantial enhancement of the branching ratio Beta(B(s)-->mu(+)mu(-)): if (g-2)(mu) exceeds the standard model prediction by 4 x 10(-9), Beta(B(s)-->mu(+)mu(-)) is larger by a factor of 10-100 and within reach of Run-II of the Tevatron. Thus the search for B(s)-->mu(+)mu(-) is a stringent test of the GUT scale relations of mSUGRA. An observation of B(s)-->mu(+)mu(-) at the Tevatron implies a mass of the lightest SUSY Higgs boson below 120 GeV. B(s)-->mu(+)mu(-) can also significantly probe SO(10) SUSY GUT models.

Correlation of Bs --> µ+µ and (g 2)µ in Minimal Supergravity

Athanasios Dedes, Herbert K. Dreiner and Ulrich Nierste 1 Physikalisches Institut, Universität Bonn, Nußallee 12, D-53115 Bonn, Germany 2 CERN, TH Division, CH-1211 Geneva 23, Switzerland We analyse the rare decay mode Bs → μ+μ− in the minimal supergravity scenario (mSUGRA). We find a strong correlation with the muon anomalous magnetic moment (g − 2)μ. An interpretation of the recently measured excess in (g − 2)μ in terms of mSUGRA corrections implies a substantial supersymmetric enhancement of the branching ratio B(Bs → μ+μ−): if (g−2)μ exceeds the Standard Model prediction by 3 ·10−9, B(Bs → μ+μ−) is larger by a factor of 100 than in the Standard Model and well within reach of Run-II of the Tevatron. Thus an experimental search for Bs → μ+μ− is a stringent test of the mSUGRA GUT scale boundary conditions. If the decay Bs → μ+μ− is observed at Run-II of the Tevatron, then we predict the mass of lightest supersymmetric Higgs boson to be less than 118 GeV. The decay Bs → μ+μ− can also significantly probe the favoured parameter range in SO(10) SUSY GUT models, possibly excluding them.

How to find a Higgs boson with a mass between 155 and 180 GeV at the CERN LHC

We reconsider the signature of events with two charged leptons and missing energy as a signal for the detection of the standard model Higgs boson in the mass region M(Higgs)=155{endash}180 GeV. It is shown that a few simple experimental criteria allow us to distinguish events originating from the Higgs boson decaying to H{r_arrow}W{sup +}W{sup {minus}} from the nonresonant production of W{sup +}W{sup {minus}}X at the CERN LHC. With this set of cuts, signal to background ratios of about one to one are obtained, allowing a 5{endash}10{sigma} detection with about 5 fb{sup {minus}1} of luminosity. This corresponds to less than one year of running at the initial lower luminosity L=10{sup 33} cm{sup {minus}2}s{sup {minus}1}. This is significantly better than for the hitherto considered Higgs boson detection mode H{r_arrow}Z{sup 0}Z{sup 0{asterisk}}{r_arrow}2scr(l){sup +}2scr(l){sup {minus}}, where in this mass range about 100 fb{sup {minus}1} of integrated luminosity are required for a 5{sigma} signal. {copyright} {ital 1997} {ital The American Physical Society}

R-parity violation at hadron colliders

Abstract Using a new operator notation we present a systematic study of all possible R-parity violating signals at a hadron collider.

R-parity violation at HERA

Abstract We summarize the signals at HERA in supersymmetric models with explicitly broken R -parity. As the most promising case, we consider in detail the resonant production of single squarks through an operator L 1 Q i D j , a production process analogous to that for leptoquarks. However, the dominant decay of the squark to a quark and a photino leads to a very different experimental signature. We examine in particular the case where the photino decays to a positron and two quarks. Using a detailed Monte Carlo procedure we obtain a discovery limit in the squark mass-Yukawa coupling plane. HERA can discover a squark for a mass as large as 270 GeV and for an R -parity violating Yukawa coupling as small as 5.8 × 10 −3 .

Anomaly-free gauged R-symmetry in local supersymmetry

We discuss local R-symmetry as a potentially powerful new model building tool. We first review and clarify that a U(1) R-symmetry can only be gauged in local and not in global supersymmetry. We determine the anomaly-cancellation conditions for the gauged R-symmetry. For the standard superpotential these equations have no solution, independently of how many Standard Model singlets are added to the model. There is also no solution when we increase the number of families and the number of pairs of Higgs doublets. When the Green-Schwarz mechanism is employed to cancel the anomalies, solutions only exist for a large number of singlets. We find many anomaly-free family-independent models with an extra SU(3)c octet chiral superfield. We consider in detail the conditions for an anomaly-free family-dependent U(1)R and find solutions with one, two, three and four extra singlets. Only with three and four extra singlets do we naturally obtain sfermion masses of the order of the weak scale. For these solutions we consider the spontaneous breaking of supersymmetry and the R-symmetry in the context of local supersymmetry. In general the U(1)R gauge group is broken at or close to the Planck scale. We consider the effects of the R-symmetry on baryon- and lepton-number violation in supersymmetry. There is no logical connection between a conserved R-symmetry and a conserved R-parity. For conserved R-symmetry we have models for all possibilities of conserved or broken R-parity. Most models predict dominant effects which could be observed at HERA.

Neutrino masses from gauge symmetries

Abstract A very simple extension of the Standard Model to include an Abelian family symmetry is able to describe the hierarchy of quark and lepton masses and their mixing angles together with the unification of gauge couplings. We consider the implications of this model for neutrino masses and mixing angles and show that they are determined up to a discrete ambiguity corresponding to the representation content of the Higgs sector responsible for the Majorana mass matrix.