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W. Grimus

Publications and source records attributed to W. Grimus.

At least 73 records · Page 4Linked to original sources
arXiv2002

Tests of CPT invariance for neutral-flavoured-meson--antimeson mixing

We focus on two aspects of CPT invariance in neutral-meson--antimeson ($M^0 \bar M^0$) mixing: 1. Tests of CPT invariance, using only the property of ``lack of vacuum regeneration'', which occurs as a part of the well-known Lee--Oehme--Yang (LOY) theory; 2. Methods for extracting the CPT-violating mixing parameter $θ$ through explicit calculations by using the LOY-type theory fully. In the latter context, we demonstrate the importance of the C-even $| M^0 \bar M^0>$ state. In particular, by measuring the time dependence of opposite-sign dilepton events arising from decays of the C-even and C-odd $| M^0 \bar M^0>$ states, $θ$ may be disentangled from the parameters $λ_+$ and $\bar λ_-$ characterizing violations of the $ΔF = ΔQ$ rule. Furthermore, these two parameters may also be determined. The same is true if one uses like-sign dilepton events arising from only the C-even $| M^0 \bar M^0>$ state.

hep-ph↗
arXiv2002

Constraining Majorana neutrino electromagnetic properties from the LMA-MSW solution of the solar neutrino problem

In this paper we use solar neutrino data to derive stringent bounds on Majorana neutrino transition moments (TMs). Should such be present, they would contribute to the neutrino--electron scattering cross section and hence alter the signal observed in Super-Kamiokande. Motivated by the growing robustness of the LMA-MSW solution of the solar neutrino problem indicated by recent data, and also by the prospects of its possible confirmation at KamLAND, we assume the validity of this solution, and we constrain neutrino TMs by using the latest global solar neutrino data. We find that all elements of the TM matrix can be bounded at the same time. Furthermore, we show how reactor data play a complementary role to the solar neutrino data, and use the combination of both data sets to improve the current bounds. Performing a simultaneous fit of LMA-MSW oscillation parameters and TMs we find that 6.3 times 10^{-10} mu_B and 2.0 times 10^{-10} mu_B are the 90% C.L. bounds from solar and combined solar + reactor data, respectively. Finally, we perform a simulation of the upcoming Borexino experiment and show that it will improve the bounds from today's data by roughly one order of magnitude.

hep-ph↗
arXiv2002

Dissipation in a 2-dimensional Hilbert space: Various forms of complete positivity

We consider the time evolution of the density matrix $ρ$ in a 2-dimensional complex Hilbert space. We allow for dissipation by adding to the von Neumann equation a term $D[ρ]$, which is of Lindblad type in order to assure complete positivity of the time evolution. We present five equivalent forms of $D[ρ]$. In particular, we connect the familiar dissipation matrix $L$ with a geometric version of $D[ρ]$, where $L$ consists of a positive sum of projectors onto planes in $\mathbf{R}^3$. We also study the minimal number of Lindblad terms needed to describe the most general case of $D[ρ]$. All proofs are worked out comprehensively, as they present at the same time a practical procedure how to determine explicitly the different forms of $D[ρ]$. Finally, we perform a general discussion of the asymptotic behaviour $t \to \infty$ of the density matrix and we relate the two types of asymptotic behaviour with our geometric version of $D[ρ]$.

quant-ph↗
arXiv2002

Soft lepton-flavor violation in a multi-Higgs-doublet seesaw model

We consider the Standard Model with an arbitrary number n_H of Higgs doublets and enlarge the lepton sector by adding to each lepton family \ell a right-handed neutrino singlet ν_{\ell R}. We assume that all Yukawa-coupling matrices are diagonal, but the Majorana mass matrix M_R of the right-handed neutrino singlets is an arbitrary symmetric matrix, thereby introducing an explicit but soft violation of all lepton numbers. We investigate lepton-flavor-violating processes within this model. We pay particular attention to the large-m_R behavior of the amplitudes for these processes, where m_R is the order of magnitude of the matrix elements of M_R. While the amplitudes for processes like tau^- --> mu^- gamma and Z --> tau^+ mu^- drop as 1/m_R^2 for arbitrary n_H, processes like tau^- --> mu^- e^+ e^- and mu^- --> e^- e^+ e^- obey this power law only for n_H = 1. For n_H \geq 2, on the contrary, those amplitudes do not fall off when m_R increases, rather they converge towards constants. This non-decoupling of the right-handed scale occurs because of the sub-process ell^- --> ell'^- {S_b^0}^*, where S_b^0 is a neutral scalar which subsequently decays to e^+ e^-. That sub-process has a contribution from charged-scalar exchange which, for n_H \geq 2, does not decrease when m_R tends to infinity. We also perform a general study of the non-decoupling and argue that, after performing the limit m_R --> \infty and removing the ν_R from the Lagrangian, our model becomes a multi-Higgs-doublet Standard Model with suppressed flavor-changing Yukawa couplings. Finally, we show that, with the usual assumptions about the mass scales in the seesaw mechanism, the branching ratios of all lepton-flavor-changing processes are several orders of magnitude smaller than present experimental limits.

hep-ph↗
arXiv2001

Softly broken lepton numbers: an approach to maximal neutrino mixing

We discuss models where the U(1) symmetries of lepton numbers are responsible for maximal neutrino mixing. We pay particular attention to an extension of the Standard Model with three right-handed neutrino singlets in which we require that the three lepton numbers L_e, L_μ, and L_τbe separately conserved in the Yukawa couplings, but assume that they are softly broken by the Majorana mass matrix M_R of the neutrino singlets. In this framework, where lepton-number breaking occurs at a scale much higher than the electroweak scale, deviations from family lepton number conservation are calculable, i.e., finite, and lepton mixing stems exclusively from M_R. We show that in this framework either maximal atmospheric neutrino mixing or maximal solar neutrino mixing or both can be imposed by invoking symmetries. In this way those maximal mixings are stable against radiative corrections. The model which achieves maximal (or nearly maximal) solar neutrino mixing assumes that there are two different scales in M_R and that the lepton number \bar L = L_e - L_μ- L_τis conserved in between them. We work out the difference between this model and the conventional scenario where (approximate) \bar L invariance is imposed directly on the mass matrix of the light neutrinos.

hep-ph↗
arXiv2001

Testing the Wigner - Weisskopf approximation by using neutral-meson - antimeson correlated states

We phenomenologically decompose the Weisskopf--Wigner approximation, as applied to the neutral flavoured meson complexes, into three pieces and propose tests for these pieces. Our tests hold for general decay amplitudes and $M^0$--$\bar M^0$ mixing parameters. We concentrate on C-odd $M^0 \bar M^0$ states and stress the importance of such tests in view of the variety of physics extracted from measurements on such complexes. Studying the feasibility of the tests confines one to the $K^0 \bar K^0$ system at present. In particular, we show that the time dependence of the correlated decay $ϕ\to K^0 \bar K^0 \to 2 (π^+ π^-)$ is determined solely by the WWA and provides thus a clean test of it.

hep-ph↗
arXiv2001

Softly broken lepton numbers and maximal neutrino mixing

We consider lepton mixing in an extension of the Standard Model with three right-handed neutrino singlets. We require that the three lepton numbers L_e, L_μ, and L_τbe separately conserved in the Yukawa couplings, and we assume that they are softly broken only by the Majorana mass matrix M_R of the neutrino singlets. In this framework, where lepton-number breaking occurs at a scale much higher than the electroweak scale, deviations from family-lepton-number conservation are calculable and finite, and lepton mixing stems exclusively from M_R. We then show that a discrete symmetry exists such that, in the lepton mixing matrix U, maximal atmospheric neutrino mixing together with U_{e3}=0 can be obtained naturally. Alternatively, if one assumes that there are two different scales in M_R and that the lepton number \bar L = L_e - L_μ- L_τis conserved in between them, then maximal solar neutrino mixing follows naturally. If both the discrete symmetry and intermediate \bar L conservation are introduced, bimaximal mixing is achieved.

hep-ph↗
arXiv2001

Bell inequality and CP violation in the neutral kaon system

For the entangled neutral kaon system we formulate a Bell inequality sensitive to CP violation in mixing. Via this Bell inequality we obtain a bound on the leptonic CP asymmetry which is violated by experimental data. Furthermore, we connect the Bell inequality with a decoherence approach and find a lower bound on the decoherence parameter which practically corresponds to Furry's hypothesis.

quant-ph↗
arXiv2001

A model for decoherence of entangled beauty

In the context of the entangled $B^0 \bar B^0$ state produced at the $Υ(4S)$ resonance, we consider a modification of the usual quantum-mechanical time evolution with a dissipative term, which contains only one parameter denoted by $λ$ and respects complete positivity. In this way a decoherence effect is introduced in the time evolution of the 2-particle $B^0 \bar B^0$ state, which becomes stronger with increasing distance between the two particles. While our model of time evolution has decoherence for the 2-particle system, we assume that, after the decay of one of the two B mesons, the resulting 1-particle state obeys the purely quantum-mechanical time evolution. From the data on dilepton events we derive an upper bound on $λ$. We also show how $λ$ is related to the so-called ``decoherence parameter'' $ζ$, which parameterizes decoherence in neutral flavoured meson--antimeson systems.

hep-ph↗
arXiv2001

4-Neutrino mass schemes and the likelihood of (3+1)-mass spectra

We examine the (3+1)-class of 4-neutrino mass spectra within a rigorous statistical analysis based on the Bayesian approach to probability. The data of the Bugey, CDHS and KARMEN experiments are combined by using a likelihood function. Our statistical approach allows us to incorporate solar and atmospheric neutrino data and also the result of the CHOOZ experiment via inequalities which involve elements of the neutrino mixing matrix and are derived from these data. For any short-baseline $Δm^2$ we calculate a bound on the LSND transition amplitude $A_{μ;e}$ and find that, in the $Δm^2$--$A_{μ;e}$ plane, there is no overlap between the 99% CL region allowed by the latest LSND analysis and the region allowed by our bound on $A_{μ;e}$ at 95% CL; there are some small overlap regions if we take the bound at 99% CL. Therefore, we conclude that, with the existing data, the (3+1)-neutrino mass spectra are not very likely. However, treating the (2+2)-spectra with our method, we find that they are well compatible with all data.

hep-ph↗
arXiv2000

Testing CPT invariance by using C-even neutral-meson--antimeson correlated states

We consider the decays of a correlated neutral-meson--antimeson state with C-parity +1. We show that there is CPT noninvariance in the mixing of the neutral mesons if, for any two decay modes f and g, the decay rate has a component R_A which is antisymmetric under the interchange of the decay times t_1 and t_2. In particular, one may cleanly extract the CPT-noninvariance parameter with the help of R_A by using opposite-sign dilepton events.

hep-ph↗
arXiv2000

Elastic $νe^-$ scattering of solar neutrinos with electromagnetic moments

We consider the azimuthal asymmetry of the recoil electrons in elastic $νe^-$ scattering of solar neutrinos, which can arise if neutrinos have electromagnetic moments and there is a large solar magnetic field. We show that using this effect it is not possible to distinguish between magnetic and electric dipole moment in the 1-Dirac and 2-Majorana neutrino cases and that averaging over neutrino energy is important and suppresses the azimuthal asymmetry in the 2-Majorana case.

hep-ph↗
arXiv2000

The seesaw mechanism at arbitrary order: disentangling the small scale from the large scale

We develop a recipe which allows one to recursively and uniquely decouple the large scale from the small scale in mass matrices of the seesaw type, up to any order in the inverse of the large scale. Our method allows one to calculate the mass matrix of the light neutrinos with arbitrary precision. The same method can be applied in the case of quark mass matrices in an extension of the Standard Model with vector-like quarks which have mass terms at a scale much higher than the electroweak scale.

hep-ph↗
arXiv2000

On a possibility to determine the S-factor of the hep process in experiments with thermal (cold) neutrons

The problem of the magnitude of the S--factor of the hep process $p + {^3\mathrm{He}} \to {^4\mathrm{He}} + e^+ + ν_e$ is one of the most important unsolved problems in nuclear astrophysics. The magnitude of $S(hep)$ has also an important impact on the interpretation of the Super-Kamiokande solar neutrino results in terms of neutrino oscillations. We point out the possiblity to determine the major hadronic contribution to $S(hep)$ from the measurement of the total cross section of the process $n + {^3\mathrm{H}} \to {^4\mathrm{He}} + e^- + \barν_e$ in experiments with high intensity beams of thermal or cold neutrons.

hep-ph↗
arXiv2000

Seesaw model with softly broken L_e - L_μ- L_τ

We enlarge the lepton sector of the Standard Model by adding to it two right-handed neutrino singlets, and propose a model based on the seesaw mechanism and on the lepton number $\bar L = L_e - L_μ- L_τ$. The model is innovative from the theoretical point of view in that the $\bar L$-invariant mass term of the right-handed neutrinos is associated with the large mass scale responsible for the seesaw mechanism, whereas $\bar L$ is softly broken at a smaller scale by the remaining Majorana mass terms of the right-handed neutrinos. While being very economical, the model has predictive power: one neutrino is massless ($m_3 = 0$), the lepton mixing matrix $U$ features $U_{e3} = 0$, and the solar-neutrino oscillations have maximal amplitude.

hep-ph↗
arXiv2000

A neutrino mass matrix with seesaw mechanism and two-loop mass splitting

We propose a model which uses the seesaw mechanism and the lepton number $\bar L = L_e - L_μ- L_τ$ to achieve the neutrino mass spectrum $m_1 = m_2$ and $m_3 = 0$, together with a lepton mixing matrix $U$ with $U_{e3} = 0$. In this way, we accommodate atmospheric neutrino oscillations. A small mass splitting $m_1 > m_2$ is generated by breaking $\bar L$ spontaneously and using Babu's two-loop mechanism. This allows us to incorporate ``just so'' solar-neutrino oscillations with maximal mixing into the model. The resulting mass matrix has three parameters only, since $\bar L$ breaking leads exclusively to a non-zero $ee$ matrix element.

hep-ph↗
arXiv2000

Elastic neutrino - electron scattering and potential effects of magnetic and electric dipole moments

We consider elastic neutrino - electron scattering of solar neutrinos with magnetic moments and electric dipole moments, where the solar neutrino state at the scattering site is determined by the evolution in matter and solar magnetic fields of the initial electron neutrino state. We present the general cross section for an arbitrary superposition of active and sterile neutrino types with positive and negative helicities, with particular emphasis on the effect of transverse polarization, which gives rise to an azimuthal asymmetry as a function of the recoil electron momentum. Within our physically motivated approximation, we perform a general CP analysis and show that in the 1-Dirac and 2-Majorana neutrino cases no CP-violating effects are present, which means that it is not possible to distinguish between magnetic and electric dipole moments in these cases. We also study the consequences of neutrino energy averaging on the cross section and stress that in the 2-Majorana neutrino case this averaging leads to a suppression of the transverse neutrino polarization effects.

hep-ph↗