arXiv subjects

M. Czakon

Publications and source records attributed to M. Czakon.

87 records · Page 5Linked to original sources

arXiv2001

In Quest of Neutrino Masses at ${\cal{O}}$(eV) Scale

Neutrino oscillation and tritium beta decay experiments taken simultaneously into account are able to access the so far imperceptible absolute neutrino masses at the electronvolt level. The neutrino mass spectrum derived in this way is independent of the nature of neutrinos (Dirac or Majorana). Furthermore, the lack of neutrinoless double beta decay gives additional constraints on the Majorana neutrino mass spectrum. A case of three neutrinos is examined. Influence of different solutions to the solar neutrino deficit problem on the results is discussed. Apart from the present situation, four qualitatively distinct experimental situations which are possible in the future are investigated: when the two decay experiments give only upper bounds on effective neutrino masses, when either one of them gives a positive result, and when both give positive results. The discussion is carried out by taking into account the present experimental errors of relevant neutrino parameters as well as their much more precise expected estimations (e.g. by $ν$ factories). It is shown in which cases the upgraded decay experiments simultaneously with neutrino oscillation data may be able to fix the absolute scale of the neutrino mass spectrum, answer the question of the neutrino nature and put some light on CP phases in the lepton sector.

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arXiv2001

Nonunitary neutrino mixing matrix and CP violating neutrino oscillations

In the standard approach to the neutrino oscillations a unitary relation among weak and mass eigenstates of light neutrinos is imposed. However, in many extensions of the SM left-handed, active neutrinos mix with additional heavy neutrino states. Consequences of this additional mixing, driven by experimental constraints, on the neutrino oscillations are considered.

hep-ph↗

arXiv2001

See-saw mechanism and four light neutrino state

A formal proof is given that in a see-saw type neutrino mass matrix with only two neutrino mass scales ($m_D \ll m_R$) and the maximal rank of $m_{R(D)}$, we can not get a fourth light sterile neutrino.

hep-ph↗

arXiv2000

Mass Spectrum and the Nature of Neutrinos

Taking as input the best fit solar neutrino anomaly description, MSW LMA, and the tritium beta decay results we estimate the allowed range of neutrino masses independently of their nature. Adding the present bound on the effective neutrino mass coming from neutrinoless double beta decay, we narrow this range for Majorana neutrinos. We complete the discussion by considering future perspectives on determining the neutrino masses, when the oscillation data will be improved and the next experiments on $(ββ)_{0ν}$ and $^3H$ decay give new bounds or obtain concrete life-times or distortions in the energy distribution.

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arXiv2000

Spectrum of neutrino masses and their nature in the light of present and future experiments

The present experimental data on neutrino oscillations, neutrinoless double beta decay and tritium beta decay are collected together and possible mass ranges for Dirac and Majorana neutrinos are found. Four future experimental situations are investigated: both decay experiments give only upper bounds, one of them gives a positive result ($|< m_ν> | \neq 0$ or $m_β\neq 0$), or finally both effective neutrino masses are different from zero ($|< m_ν> | \neq 0$ and $m_β\neq 0$). Each scenario gives new information on neutrino masses and nature but only the last has a chance to resolve the problem and give some additional information on CP violation in the lepton sector.

hep-ph↗

arXiv2000

GENIUS project, neutrino oscillations and Cosmology: neutrinos reveal their nature?

The neutrinoless double beta decay as well as any other laboratory experiment has not been able to answer the question of the neutrino's nature. Hints on the answer are available when neutrino oscillations and $(ββ)_{0 ν}$ are considered simultaneously. In this case phenomenologically interesting neutrino mass schemes can lead to non-vanishing and large values of $ $. As a consequence, some schemes with Majorana neutrinos can be ruled out even now. If we assume that in addition neutrinos contribute to Hot Dark Matter then the window for Majorana neutrinos is even more restricted, e.g. GENIUS experiment will be sensitive to scenarios with three Majorana neutrinos.

hep-ph↗

arXiv2000

Single chargino production with R-parity lepton number violation in electron-electron and muon-muon collisions

We examine single chargino production in conjunction with R-parity lepton number violation in future lepton-lepton collisions. Present bounds on R-parity violating couplings allow for a production cross section of the order of ${\cal{O}} (10 {fb})$ for a wide range of sneutrino and chargino masses. Scenarios of chargino decay which lead to purely leptonic signals in the final state and without missing energy are also discussed.

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arXiv2000

Perspectives on Finding the Neutrino Nature

The possibility of determining the neutrino nature is considered in view of the most recent experimental observations. The analysis combines schemes with three and four neutrinos.The data on oscillations is put together with that from the search of neutrinoless double beta decay and results on tritium beta decay. All solar neutrino oscillation solutions are taken into account. The sensitivity of the problem on future experimental bounds from GENIUS is studied. Dirac neutrinos are shown to be unavoidable already at present in some schemes and the constraints will quickly become more stringent with future data. The consequences of including bounds from Cosmology on the neutrino content of Hot Dark Matter are commented.

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arXiv1999

Are Neutrinos Dirac or Majorana Particles?

In spite of the general belief that neutrinos are Majorana particles, their character should be revealed experimentally. We begin by discussing why it is so difficult in terrestrial experiments. If neutrinos are Majorana particles, the first signal should come from neutrinoless double $β$ decay. Still the search for such a decay of various nuclei is negative. We outline how the present knowledge of neutrino masses and mixing matrix elements combined with the bound from $(ββ)_{0ν}$ decay could help to determine their nature.

hep-ph↗

arXiv1999

Radiative Corrections to the Left-Right Model

The oblique part of the radiative corrections to the Left-Right model is described. The leading non-logarithmic terms are explicitly written. It is argued, on the basis of a comparison with the Standard Model, that one cannot use the loop contributions of the latter to refine phenomenological analyses of the Left-Right model, and by the same of any general extension.

hep-ph↗

arXiv1999

Nature of neutrinos in the light of present and future experiments

Two general models with hierarchical and almost degenerate neutrino masses, which are able to explain the solar and atmospheric anomalies are investigated. We show how neutrinoless double beta decay experiments discern Dirac and Majorana natures of neutrinos. The strongest result is, that almost degenerate neutrinos with masses above 0.22 eV combined with the SMA MSW must be Dirac particles. In the general case, the same bound is true for specific parity assignments. In the near future (GENIUS experiment), one of the hierarchical schemes, and the VO mechanism for almost degenerate neutrinos and specific mixing matrix elements and parity assignments will be tested.

hep-ph↗

arXiv1999

Confronting electroweak precision measurements with New Physics models

Precision experiments, such as those performed at LEP and SLC, offer us an excellent opportunity to constrain extended gauge model parameters. To this end, it is often assumed, that in order to obtain more reliable estimates, one should include the sizable one--loop Standard Model (SM) corrections, which modify the $Z^0$ couplings as well as other observables. This conviction is based on the belief that the higher order contributions from the ``extension sector'' will be numerically small. However, the structure of higher order corrections can be quite different when comparing the SM with its extension, thus one should avoid assumptions which do not care about such facts. This is the case for all models with $ρ_{\rm tree} \equiv M_W^2/(M_{Z}^2\cos^2{Θ_W}) \neq 1$. As an example, both the manifest left-right symmetric model and the $SU(2)_L \otimes U(1)_Y \otimes \tilde{U}(1)$ model, with an additional $Z'$ boson, are discussed and special attention to the top contribution to $Δρ$ is given. We conclude that the only sensible way to confront a model with the experimental data is to renormalize it self-consistently, if not, parameters which depend strongly on quantum effects should be left free in fits, though essential physics is lost in this way. We should note that arguments given here allow us to state that at the level of loop corrections (indirect effects) there is nothing like a ``model independent global analysis'' of the data.

hep-ph↗

arXiv1999

Left-right symmetry and heavy particle quantum effects

We have renormalized a classical left-right model with a bidoublet, and left and right triplets in the Higgs sector. We focus on oblique corrections and show the interplay between the top quark, heavy neutrinos and Higgses contribution to the muon $Δr$ parameter. In the SM, custodial symmetry prevents large oblique corrections to appear. Although in LR models there is no such symmetry to make vanish the quadratically diverging terms, we have shown, that heavy Higgses contributions to $Δr$ are under control. Also the top contribution to $Δr$, quite different from that in the SM, is discussed. However, heavy neutrinos seem to give the most important contributions. From oblique corrections, they can be as large as the SM top one. Moreover, vertex and box diagrams give additional non-decoupling effects and only concrete numerical estimates are able to answer whether the model is still self-consistent.

hep-ph↗

arXiv1999

Low energy physics and left-right symmetry. Bounds on the model parameters

In any gauge model with spontaneous symmetry breakdown the gauge boson masses and their mixings are not independent quantities. They are interconnected through the vacuum expectation values (VEVs) of the Higgs sector. We discuss the low-energy experiments, namely electron-hadron, neutrino-hadron and neutrino-electron processes in the frame of the Manifest Left-Right Symmetric model and show the impact of these dependencies on the possible heavy gauge boson masses and mixings. At 90 % C.L., we obtain $M_{Z_2} \geq 1475$ GeV for phenomenologically favorable models, without $W_L-W_R$ mixing and $M_{Z_2} \geq 1205$ GeV in the other extreme case when a maximal mixing is possible. If we consider the \lr parameters without any constraints from the Higgs sector these limits get down to 410 GeV. Bounds on the Z_2 mixing angle as well as the W_2 mass and its mixing angle are also given.

hep-ph↗

arXiv1998

Majorana neutrino transition magnetic moments in left-right symmetric models

Transition magnetic moments of Majorana neutrinos are discussed in the frame of the most natural version of the LR model (with left- and right-handed triplets and a bidoublet in the Higgs sector). We show that their largest values could be at most $6\cdot 10^{-13} μ_B$ from diagrams with $W_L$ in the loop. This could happen for specific models where (i) neutrino-charged lepton mixing is maximal and (ii) $κ_1 \simeq κ_2$ (VEVs for neutral Higgs fields in the bidoublet $ϕ$ are equal). Contributions from diagrams with charged Higgses in the loop are smaller than those in the SM with right-handed neutrinos.

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