arXiv subjects

E. A. Paschos

Publications and source records attributed to E. A. Paschos.

At least 19 recordsLinked to original sources

arXiv2021

Flavor changing neutral couplings for leptons

The article reviews the conditions for lepton-flavor conservation in leptonic interactions. The conditions are similar to those developed in the quark sector. For neutrinos the mass eigenstates are unitary superpositions of flavor states which together with small mass differences produce neutrino oscillations. A new property for neutrinos is the fact that their masses are very small suppressing their couplings to neutral scalar fields. The results are demonstrated in several models.

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arXiv2021

A Light Mediator Relating Neutrino Reactions

The extension of the standard model with a multiplicative $U(1)_R$ factor is consistent with a light vector boson. In its simplest realization, only right-handed particles carry charges of the new group. In this model, there is a residual $τ_{3R}$ symmetry and one new coupling constant which correlates neutrino interactions. We compute new contributions to antineutrino$-$electron scattering and coherent scattering on nuclei, and compare them with the XENON1T result.

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arXiv2020

A chiral gauge-invariant model for Majorana neutrinos

The article investigates the possibility that right-handed neutrinos are Majorana particles embedded in an abelian multiplicative $U(1)_R$ factor, with the Lagrangian in the new factor being invariant under chiral gauge transformations. Majorana neutrinos couple to charged and neutral currents, producing new signatures to (anti)neutrino-electron elastic scattering and an additional term to coherent scattering of neutrinos on atomic nuclei. The model is ultraviolet complete and depends on one extra hypercharge correlating the reactions and providing upper bounds for the new coupling constant.

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arXiv2018

Searching for new light gauge bosons at $e^+e^-$ colliders

Neutral gauge bosons beyond the Standard Model are becoming interesting as possible mediators to explain several experimental anomalies. They have small masses, below one GeV, and are referred to as dark photons, $U$, $A'$ or $Z'$ bosons. Electron--positron collision experiments at the B-factories provide the most straightforward way to probe bosons of this kind. In the present article we study production of the bosons at $e^+e^-$ colliders operating at GeV center-of-mass energies. We have studied two channels: $e^+e^-\rightarrow γZ'$ and $e^+e^-\rightarrow e^+e^-Z'$. Analytic expressions for the cross sections and various observables such as the energy spectra of the produced bosons and the final electrons from the $Z'$ decays are derived. We have also studied the transverse momentum distribution of the bosons and the spatial distribution of the $Z'\rightarrow e^+e^-$ decay vertices. It is shown that these distributions provide distinct signatures of the bosons in $e^+e^-\rightarrowγZ'$. The reaction $e^+e^-\rightarrow e^+e^-Z'$ becomes important at small $Z'$ scattering angles where its contribution to the overall yield may be larger by orders of magnitude compared to $e^+e^-\rightarrowγZ'$. The standard processes $e^+e^-\rightarrowγγ$ and $e^+e^-\rightarrow e^+e^-γ$ that lead to the same signal are considered. We include numerical predictions for the production rates at the energy $\sqrt{s}=10.5$ GeV. The case with a light scalar boson is also discussed. The calculations are performed in detail and can be useful for additional studies.

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arXiv2017

Open Issues in Neutrino Reactions

Numerous investigations discuss neutrino properties from low to ultra high energies. This review discusses several topics that are investigated in present day experiments. The first section covers the detection of $τ$-neutrinos of cosmic origin and describes the significance of the results. The second topic points out that the reported reduction of the antineutrino flux in reactor experiments may be created by short wavelength oscillations where the detector averages over several wavelengths and observes only an average reduction of the antineutrino flux. In many theories the propagating particles are Majoranas and have an anapole moment; they scatter on atomic electrons with a distinct signature in $\barν_e+e^-\rightarrow\barν_e+e^-$ scattering.

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arXiv2016

Distributions for tau neutrino interactions observed through the decay $τ\rightarrow μν_τ\barν_μ$

We investigate the problem of identifying $ν_τ$-induced reactions in large neutrino telescopes. We concentrate on events with tracks and showers where the respective energies $E_μ$ and $E_X$ are measured separately. Then we compute analytically and numerically event distributions in two variables $r_l = E_X/E_l$ and $y'=E_{\text{X}}/(E_μ+E_{X})$. We find that the $y'$-distribution is especially useful because in the $ν_τ$-induced reactions the distribution has a minimum at $y'=0.75$ and then increases as $y'\rightarrow1$. This is different in $ν_μ$-induced reactions where the $y'$-distribution decreases monotonically. The results are demonstrated with figures where one can estimate the required sensitivity of the experiments. Another attractive property is that in several ratios the neutrino flux factorizes and drops out. We hope the results of this article will be useful for searches of tau (anti)neutrinos of energies above 100 GeV to several TeV in the present and planned large volume neutrino telescopes.

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arXiv2014

Aspects of Neutrino Interactions (Scattering at small $Q^2$- Region)

The article begins with a description of chiral symmetry and its application to neutrino induced reactions. For small $Q^2$ (forward direction) the process is dominated by the amplitute with helicity zero where the pion pole disappears when multiplied with the polarization vector. The remaining part of the amplitude is determined by PCAC. For $E_ν> 2$ GeV the computed cross sections are in good agreement with data. In coherent pion production we expect equal yields for neutrinos and antineutrinos a relation which for $E_ν> 2$ GeV is fulfilled. We discuss specific features of the data and suggest methods for improving them by presenting new estimates for the incoherent background.

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arXiv2014

Comparison of the ANP model with the data for neutrino induced single pion production from the MiniBooNE and MINER$ν$A experiments

We present theoretical predictions in the framework of the ANP model for single pion production ($π^+, π^0$) in $ν_μ$ and $\barν_μ$ scattering off mineral oil and plastic. Our results for the total cross sections and flux averaged differential distributions are compared to all available data of the MiniBooNE and MINER$ν$A experiments. While our predictions slightly undershoot the MiniBooNE data they reproduce the normalization of the MINER$ν$A data for the kinetic energy distribution. For the dependence on the polar angle we reproduce the shape of the arbitrarily normalized data.

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arXiv2014

Angular Dependence of Coherent Pion Production by Neutrinos

Coherent pion production by neutrinos has been interpreted in the framework of the Partially Conserved Axial Current hypothesis (PCAC) and explicit model calculations are available. In this article we compute angular correlations for the produced pions which may help to separate the signal from the background. We present many figures useful for the experiments and compare them with another model.

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arXiv2013

Neutrino-induced pion production at low energies and in the small $Q^2$ region

We analyse neutrino-induced reactions in the small $Q^2$ region and for energies covering the production and decay of the delta resonance. One of our results is the agreement with the MiniBooNE data for $1π^+$ and $1π^0$ final states. In addition we present differential cross sections for charged and neutral currents and for proton and neutron targets. Finally, we present cross sections induced by muon and electron type neutrinos, where effects of the lepton masses are visible.

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arXiv2012

Pion production by neutrinos in the delta resonance region and possible application to CP searches

We present the results of extensive calculations for charged and neutral current reactions of neutrinos and antineutrinos in the small $Q^2\lsim\unit[0.20]{GeV^2}$ region. The results include single $\frac{\d σ}{\d Q^2}$ and double $\frac{\d σ^{(A)}}{\d Q^2 \d E_π}$ differential cross sections at energies relevant for oscillation experiments. We include nuclear corrections in the Adler-Nussinov-Paschos model and point out that on isoscalar nuclear targets there are charge symmetry relations that hold in extended kinematic regions. We discuss how the results can be used in long baseline experiments in order to study oscillation parameters and search for CP asymmetries.

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arXiv2011

Neutrino production of hadrons at low energy and in the small $Q^2$ region

We use PCAC in the small $Q^2$ region in order to calculate the Adler sum rule and the production of hadrons in the low energy region where resonances dominate. We find very good agreement with the sum rule and with the computed cross sections. We find a value $C_5^A(0)$ close to the Goldberger-Treiman prediction. The formalism is general and can be applied to other reactions shedding light into the dynamical transition from resonances to deep inelastic scattering.

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arXiv2009

Coherent Pion Production by Neutrinos

In this talk I review the main features of the coherent/diffractive pion production by neutrinos on nuclei. The method is based on PCAC and relates the reaction $\textbf{boson} + \textbf{nucleus} \to \textbf{pion} + \textbf{nucleus}$ to elastic pion-nucleus scattering. Estimates for the expected rates and distributions in neutrino reactions are presented with the help of hadronic data. The absolute rates are significantly smaller than the older estimates which brings theory in agreement with the neutral current measurements and the bounds in charged current reactions.

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arXiv2009

Coherent Pion Production

In this paper we present quantitative results for coherent pion production by neutrinos scattered off nuclei within the framework developed by Gounaris, Kartavtsev and Paschos. The method is based on PCAC and uses helicity cross sections for the scattering of weak gauge bosons on nuclei. The process relies on experimental data for elastic pion-nucleus scattering. A detailed analysis of the differential and integrated cross sections is presented for neutral and charged currents, with special emphasis on the regions of integrations. The results are extended to energies of 10.0 GeV and are compared with experimental data.

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arXiv2008

Pion Spectra in the Production of Resonances by Neutrinos

A method is presented using helicity cross sections for calculating neutrino-nucleon interactions. The formalism is applied in the calculation of the pion spectra produced by nu_mu and nu_tau beams. The masses of the charged leptons are kept throughout the calculations. Cross sections are presented in numerous figures where the contributions of the significant form factors are also shown. The article describes the steps of the calculation and gives details so that it can be reproduced and adapted to the kinematic conditions of the experiments.

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arXiv2007

Coherent Pion Production by Neutrinos

I concentrate in this article on the reaction--coherent pion production by neutrinos incident on nuclei. A special effort is made in order to describe the approximations entering the calculation. I conclude that the reaction is well understood and with appropriate data for hadronic reactions is can be computed for low and high energies. Because of shortage of space I omitted the resonance analysis, which is described in articles with my collaborators.

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arXiv2007

Single pion electro-- and neutrinoproduction on heavy targets

We present a calculation of single pion electroproduction cross sections on heavy targets in the kinematic region of the Delta(1232) resonance. Final state interactions of the pions are taken into account using the pion multiple scattering model of Adler, Nussinov and Paschos (ANP model). For electroproduction and neutral current reactions we obtain results for carbon, oxygen, argon and iron targets and find a significant reduction of the W-spectra for pi^0 as compared to the free nucleon case. On the other hand, the charged pion spectra are only little affected by final state interactions. Measurements of such cross sections with the CLAS detector at JLAB could help to improve our understanding of pion rescattering effects and serve as important/valuable input for calculations of single pion neutrinoproduction on heavy targets relevant for current and future long baseline neutrino experiments. Two ratios, in Eq. (3.8) and (3.10), will test important properties of the model.

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arXiv2006

Neutrino Phenomenology, Dark Energy and Leptogenesis from pseudo-Nambu-Goldstone Bosons

We consider a model of dynamical neutrino masses via the see-saw mechanism. Nambu-Goldstone bosons (majorons) arise associated with the formation of the heavy right-handed majorana masses. These bosons then acquire naturally soft masses (become pNGB's) at loop level via the Higgs-Yukawa mass terms. These models, like the original neutrino pNGB quintessence schemes of the 1980's that proceed through the Dirac masses, are natural, have cosmological implications through mass varying neutrinos, long range forces, and provide a soft potential for dark energy. We further argue that these models can explain leptogenesis naturally through the decays of the right-handed neutrinos.

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