arXiv subjects

D. Falcone

Publications and source records attributed to D. Falcone.

36 records · Page 2Linked to original sources

arXiv2001

Baryon asymmetry and mass matrices

In the framework of the baryogenesis via leptogenesis mechanism we study the link between the amount of baryon asymmetry and neutrino mass matrices. In particular, neglecting phases, we find that if the Dirac neutrino mass matrix is related to the up quark mass matrix, the baryon asymmetry is about three orders smaller than the required value. If the Dirac neutrino mass matrix is related to the down quark or the charged lepton mass matrix, the baryon asymmetry is about two orders smaller than the required value. In order to get a sufficient amount of baryon asymmetry we need a more moderate hierarchy in the Dirac neutrino mass matrix.

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arXiv2001

Baryogenesis via leptogenesis in SO(10) models

We discuss the baryogenesis via leptogenesis mechanism within the supersymmetric and nonsupersymmetric SO(10) models. We find that the nonsupersymmetric model, endowed with an intermediate scale, is generally favoured, unless some fine tuning occurs in the supersymmetric case.

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arXiv2001

Model for fermion mass matrices and the origin of quark-lepton symmetry

Several phenomenological features of fermion masses and mixings can be accounted for by a simple model for fermion mass matrices, which suggests an underlying U(2) horizontal symmetry. In this context, it is also proposed how an approximate quark-lepton symmetry can be achieved without unified gauge theories.

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arXiv2001

Fermion masses and mixings in gauge theories

The recent evidence for neutrino oscillations stimulate us to discuss again the problem of fermion masses and mixings in gauge theories. In the standard model, several forms for quark mass matrices are equivalent. They become ansatze within most extensions of the standard model, where also relations between quark and lepton sectors may hold. In a seesaw framework, these relations can constrain the scale of heavy neutrino mass, which is often related to the scale of intermediate or unification gauge symmetry. As a consequence, two main scenarios arise. Hierarchies of masses and mixings may be explained by broken horizontal symmetries.

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arXiv2001

Neutrino oscillations and neutrinoless double beta decay

The relation between neutrino oscillation parameters and neutrinoless double beta decay is studied, assuming normal and inverse hierarchies for Majorana neutrino masses. For normal hierarchy the crucial dependence on U_{e3} is explored. The link with tritium beta decay is also briefly discussed.

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arXiv2001

Leptogenesis with SU(5)-inspired mass matrices

In the baryogenesis via leptogenesis framework the baryonic asymmetry depends on lepton mass matrices. In a previous paper we used SO(10)-inspired mass matrices and we found few possibilities to obtain a sufficient level of asymmetry. In the present paper we use SU(5)-inspired mass matrices, which also allow to check the dependence of the baryonic asymmetry on Dirac neutrino masses. In particular, we find that the large mixing matter solution to the solar neutrino problem, which within SO(10) gives too small asymmetry, can now be favoured.

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arXiv2000

Leptogenesis and neutrino parameters

We calculate the baryonic asymmetry of the universe in the baryogenesis-via-leptogenesis framework, assuming first a quark-lepton symmetry and then a charged-neutral lepton symmetry. We match the results with the experimentally favoured range. In the first case all the oscillation solutions to the solar neutrino problem, except the large mixing matter solution, can lead to the allowed range, but with fine tuning of the parameters. In the second case the general result is quite similar. Some related theoretical hints are discussed.

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arXiv2000

Talk on fermion masses and mixings

Two topics are covered in this paper. In the first part the relation between quark mass matrices and observable quantities in gauge theories. In the second part neutrino masses and mixings in a seesaw framework.

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arXiv2000

Seesaw mechanism, quark-lepton symmetry and Majorana phases

A previous short analysis of the seesaw mechanism, based on quark-lepton symmetry, experimental data and hierarchical neutrino spectrum, is enlarged to include small but not zero U_{e3}, inverted mass hierarchy, and the qualitative effect of Majorana phases. The structure of the heavy neutrino mass matrix obtained in several cases is discussed. We find two leading forms for this matrix. One is diagonal and stands at the unification scale or above. The other is off-diagonal and stands at the intermediate scale.

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arXiv2000

Neutrino masses and mixings in SO(10)

Assuming a Zee-like matrix for the right-handed neutrino Majorana masses in the see-saw mechanism, one gets maximal mixing for vacuum solar oscillations, a very small value for $U_{e3}$ and an approximate degeneracy for the two lower neutrino masses. The scale of right-handed neutrino Majorana masses is in good agreement with the value expected in a SO(10) model with Pati-Salam $SU(4)\ts SU(2)\ts SU(2)$ intermediate symmetry.

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arXiv2000

Testing quark mass matrices with right-handed mixings

In the standard model, several forms of quark mass matrices which correspond to the choice of weak bases lead to the same left-handed mixings $V_L=V_{CKM}$, while the right-handed mixings $V_R$ are not observable quantities. Instead, in a left-right extension of the standard model, such forms are ansatze and give different right-handed mixings which are now observable quantities. We partially select the reliable forms of quark mass matrices by means of constraints on right-handed mixings in some left-right models, in particular on $V^R_{cb}$. Hermitian matrices are easily excluded.

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arXiv2000

Heavy neutrino mass scale and quark-lepton symmetry

Assuming hierarchical neutrino masses we calculate the heavy neutrino mass scale in the seesaw mechanism from experimental data on oscillations of solar and atmospheric neutrinos and quark-lepton symmetry. The resulting scale is around or above the unification scale, unless the two lightest neutrinos have masses of opposite sign, in which case the resulting scale can be intermediate.

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arXiv1999

Neutrino masses and mixings in a seesaw framework

Assuming the seesaw mechanism for hierarchical neutrino masses, we calculate the heavy neutrino masses under the hypotheses that the mixing in the Dirac leptonic sector is similar to the quark mixing ($V_D \sim V_{CKM}$) and that $M_ν \sim M_u$ or $M_e$, where $M_ν$ is the Dirac mass matrix of neutrinos. As a result we find that for $M_ν \sim M_u$ the vacuum oscillation solution of the solar neutrino problem leads to a scale for the heavy neutrino mass well above the unification scale, while for the MSW solutions there is agreement with this scale. For $M_ν \sim M_e$ the vacuum solution is consistent with the unification scale, and the MSW solutions with an intermediate scale. The mass of the lightest heavy neutrino can be as small as $10^5$ GeV.

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arXiv1999

Quark mass matrices and observable quantities

A nearly historical account of quark mass matrix models is given, and the structure of quark mass matrices in the Standard Model is studied. For a minimal parameter basis suggested earlier, where $M_u$ is diagonal and $M_{d11}$, $M_{d13}$, $M_{d31}$ are zero, the dependence of mass matrices on the CP violating phase $δ$ of $V_{CKM}$ is reported: all parameters are almost independent, except $M_{d22}$ and $M_{d23}$, and the equality $|M_{d22}|=M_{d23}$ is obtained for a value of $δ$ very close to the value which is favoured by experiments. Moreover, on this basis, $M_{d12} \simeq M_{d21}$ and $M_{d33} \simeq 2M_{d32}$. Some comments on mass matrices in left-right symmetric models are added.

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arXiv1998

Lepton mass matrices from a quark-lepton analogy

We study the implications of having a similarity between quark and lepton mixing in the Dirac sector of the Standard Model plus the right-handed neutrino. This enable us to describe all masses and mixings in the Dirac sector in terms of only five parameters: three mass scales $m_b$, $m_τ$ and $m_t$, one parameter $λ$ describing all the mixings, and a CP violating phase in the quark sector. Then, from experimental data on neutrino masses and mixings, we extract the heavy neutrino mass matrix. The approach considered, although does not contraddict Grand Unified Theories, can help to find other theoretical models of fermion masses.

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arXiv1998

Phenomenological Bounds on B to Light Semileptonic Form Factors

The form factors for the weak currents between B and light mesons are studied by relating them to the corresponding D form factors at q^2_{max} according to HQET, by evaluating them at q^2=0 by QCD sum rules, and by assuming a polar q^2 dependence. The results found are consistent with the information obtained from exclusive non-leptonic two-body decays and, with the only exception of A_1, with lattice calculations.

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arXiv1998

Relation between quark masses and weak mixings

Simple transformation formulas between fermion matrices and observables, and numerical values of quark matrices, are obtained on a particular weak basis with one quark matrix diagonal and the other with vanishing elements 1-1, 1-3 and 3-1, and with only the element 2-2 complex. When we choose $M_u$ diagonal, then $M_d$ shows intriguing numerical properties which suggest a four parameter description of it, which implies $V_{us}\simeq \sqrt{m_d/m_s}$, $V_{cb}\simeq (3/\sqrt{5})(m_s/m_b)$ and $V_{ub}\simeq (1/\sqrt{5})(\sqrt{m_d m_s}/m_b)$. Few comments on mass-mixing relations are added.

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arXiv1997

Fermion Mass Matrices in term of the Cabibbo-Kobayashi-Maskawa Matrix and Mass Eigenvalues

A parameter free, model independent analysis of quark mass matrices is carried out. We find a representation in terms of a diagonal mass matrix for the down (up) quarks and a suitable matrix for the up (down) quarks, such that the mass parameters only depend on the six quark masses and the three angles and phase appearing in the Cabibbo-Kobayashi-Maskawa matrix. The results found may also be applied to the Dirac mass matrices of the leptons.

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