arXiv subjects

P. Bamert

Publications and source records attributed to P. Bamert.

12 recordsLinked to original sources

arXiv1997

Helioseismology, MSW and the Solar Neutrino Problem

In this talk I summarize recent work done in collaboration with Cliff Burgess and Denis Michaud, in which we performed a detailed investigation of how solar neutrinos propagate through helioseismic waves. We find that the MSW solar neutrino spectrum is not modified at all in the presence of seismic waves. This finding differs from earlier estimates mainly because most helioseismic waves are too weak in the vicinity of the MSW resonance to be of relevance for neutrino propagation. A special class of waves may however by subject to an instability and potentially have very large amplitudes. These waves do have long wavelengths, a situation for which the formalism employed in earlier analyses does not apply. Our numerical simulation significantly reduces their influence on neutrino propagation.

hep-ph↗

arXiv1997

Neutrino Propagation Through Helioseismic Waves

Motivated by earlier calculations showing large effects when neutrinos propagate through fluctuating media, we perform here a detailed analysis of how density fluctuations in the sun in the form of helioseismic waves can modify the MSW solution to the solar neutrino problem. We find negligible effects for the MSW spectrum, even under extreme circumstances. There are two main reasons why our conclusions differ from earlier analyses. First, most helioseismic waves do not affect neutrino propagation because their amplitude is too small in the MSW resonance region, which is the only region to whose fluctuations neutrinos are sensitive. There is one class of waves which may be subject to an instability, however, and so can have significantly larger amplitudes. But the wavelength for these waves is so long that it invalidates the previous methods of calculation. Our more complete calculation significantly reduces the prediction for their influence on neutrino propagation.

hep-ph↗

arXiv1996

R_b and New Physics: A Comprehensive Analysis

We survey the implications for new physics of the discrepancy between the LEP measurement of $R_b$ and its Standard Model prediction. Two broad classes of models are considered: ($i$) those in which new $Z\bbar b$ couplings arise at tree level, through $Z$ or $b$-quark mixing with new particles, and ($ii$) those in which new scalars and fermions alter the $Z \bbar b$ vertex at one loop. We keep our analysis as general as possible in order to systematically determine what kinds of features can produce corrections to $R_b$ of the right sign and magnitude. We are able to identify several successful mechanisms, which include most of those which have been recently been proposed in the literature, as well as some earlier proposals (\eg\ supersymmetric models). By seeing how such models appear as special cases of our general treatment we are able to shed light on the reason for, and the robustness of, their ability to explain $R_b$.

hep-ph↗

arXiv1996

Rb and Heavy Quark Mixing

In this talk I summarize a part of the work done in a recent collaboration with C. Burgess, J. Cline, D. London and E. Nardi \cite{b96}. We analyze the observed discrepancy between $R_b(\equiv\gb /\ghad )$ as measured at LEP and its standard model value for signals of new physics. The focus is thereby put on new physics that manifests itself through heavy quark mixing. Heavy quark mixing affects the measured value of $R_b$ in two ways: at tree level (bottom mixing) and at one-loop level (top mixing). One finds that whereas the latter cannot account for the deviation, bottom mixing can in principle do the job.

hep-ph↗

arXiv1996

R(b), R(c) and New Physics: An Updated Model Independent Analysis

We analyze LEP and SLC data from the 1995 Summer Conferences as well as from low energy neutral current experiments for signals of new physics. The reasons for doing this are twofold, first to explain the deviations from the standard model observed in $R_b$ and $R_c$ and second to constrain non-standard contributions to couplings of the $Z^0$ boson to all fermions and to the oblique parameters. We do so by comparing the data with the Standard Model as well as with a number of test hypotheses concerning the nature of the new physics. These include non-standard $Zb\bar{b}$-, $Zc\bar{c}$- and $Zs\bar{s}$-couplings as well as the couplings of the $Z^0$ to fermions of the entire first, second and third generations and universal corrections to all up- and down-type quark couplings (as can arise \eg\ in $Z'$ mixing models). We find that non-standard $Zb\bar{b}$ couplings are both necessary and sufficient to explain the data and in particular the $R_b$ anomaly. It is not possible to explain $R_b$, $R_c$ and a value of the strong coupling constant consistent with low energy determinations invoking only non-standard $Zb\bar{b}$- and $Zc\bar{c}$-couplings. To do so one has to have also new physics contributions to the $Zs\bar{s}$ or universal corrections to all $Zq\bar{q}$ couplings.

hep-ph↗

arXiv1995

NEW PHYSICS AND RECENT HIGH PRECISION ELECTROWEAK MEASUREMENTS

We analyze LEP and SLC data from the 1995 Winter Conferences for signals of new physics. We compare the data with the Standard Model (SM) as well as a number of test hypotheses concerning the nature of new physics: (i) nonstandard Zbb couplings, (ii) nonstandard Zff couplings for the entire third generation, (iii) nonstandard oblique corrections, (iv) nonstandard lepton couplings, (v) general nonstandard W and Z couplings to all fermions, as well as combinations of the above. In most of our analyses, we leave the SM variables $α_s$ and $m_t$ as free parameters to see how the various types of new physics can affect their inferred values. We find that the best fit ($χ^2/d.o.f. = 8.4/10$) is obtained for the nonstandard Zbb couplings, which also give a `low' value (0.112) for $α_s$. The SM also gives a good description of the Z data, having $χ^2/d.o.f. = 12.4/12$. If $α_s$ is held fixed to the low-energy value 0.112, then we find that a combination of the nonstandard Zbb couplings is fit to lie more than four standard deviations away from zero.

hep-ph↗

arXiv1995

THE SENSITIVITY TO NEW PHYSICS OF A LEP SCAN IN 1995

We study the implications of possible off-peak measurements in the 1995 LEP run, in regard to probing physics beyond the Standard Model. To do so, we determine the accuracy with which various nonstandard couplings can be expected to be measured in the three different scan scenarios recently discussed by Clarke and Wyatt. We find that each scan scenario allows greater sensitivity to a different set of new physics couplings. Oblique parameters are best measured with the longest scan, while nonstandard fermion couplings to the Z tend to be better constrained (albeit only marginally) if all of the 1995 LEP measurements are taken on the Z peak.

hep-ph↗

arXiv1995

Multi-Majoron Modes for Neutrinoless Double-Beta Decay

We construct two new classes of models for double beta decay, each of which leads to an electron spectrum which differs from the decays which are usually considered. One of the classes has a spectrum which has not been considered to date, and which is softer than the usual two-neutrino decay of the Standard Model. We construct illustrative models to show how other phenomenological bounds can be accommodated. We typically find that, although all other bounds can be satisfied, the predicted double-beta decay rate only in one class of these models is at best large enough to be just detectable in current experiments.

hep-ph↗

arXiv1994

Heavy Sterile Neutrinos and Neutrinoless Double Beta Decay

We investigate the possibility of producing neutrinoless double beta decay without having an electron neutrino with a mass in the vicinity of 1 eV. We do so by having a much lighter electron neutrino mix with a much heavier (m > 1 GeV) sterile neutrino. We study the constraints on the masses and mixings of such heavy sterile neutrinos from existing laboratory, astrophysical and cosmological information, and discuss the properties it would require in order to produce a detectable signal in current searches for neutrinoless double beta decay.

hep-ph↗

arXiv1994

Negative s and Light New Physics

Motivated by the difference between SLD's recent measurement of ALR and the corresponding LEP results, we explore which kinds of new particles can (1) contribute dominantly to new physics through oblique corrections, (2) produce negative values for S and T, and (3) not be in conflict with any other experiments, on or off the Z resonance. We are typically led to models which involve new particles which are not much heavier than MZ/2, and so which may also have implications for other experiments in the near future. For such light particles, we show how the oblique-parameter analysis of purely Z-pole data requires the interpretation of the data in terms of modified parameters, S' and T', whose difference from S and T improves the available parameter space of the models.

hep-ph↗

arXiv1994

Naturally Degenerate Neutrinos

The solar neutrino problem, atmospheric neutrino problem, and the existence of hot dark matter can all be economically accounted for using only the three known neutrinos if these neutrinos all have nearly degenerate masses of a few eV. We show how to generate this pattern of neutrino masses in a natural way within a `see-saw' framework.

hep-ph↗

arXiv1993

Gauge boson masses dominantly generated by Higgs-triplet contributions?

We discuss a model in which the Standard Model (SM) Higgs sector has been extended by additional real and complex triplets. The $ρ\approx 1$ constraint is satisfied by restricting the potential to have an enlarged $\hisym $ global symmetry. This is fine tuning, which leads to a decreased predictability in next-to-leading order. In this model, however, the triplet vacuum expectation values may give the dominating contribution to the gauge boson masses. Using a renormalization group argument we constrain this region of the parameter space. Another interesting feature of this model is that one of the neutral scalars doesn't couple to the fermion sector at tree level and therefore could have a relatively large branching ratio to $2γ$'s. It is coupled, however, to the $Z$-boson and therefore it could be produced at LEP via the standard $e^+e^-\rightarrow Zϕ$ mechanism with rates comparable to the ones of the Standard Model.

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