2,217 research outputs found
The emergence of the Cabibbo angle in non-degenerate coupled systems of fermions
Investigating, in direct continuation of our previous paper hep-ph/0606303
the implications of the non-unitarity of mixing matrices for non-degenerate
coupled systems that we demonstrated there, we examine more accurately the
vicinity of Cabibbo-like mixing in quantum field theory. We show that it is
possible to preserve one of its main features, namely that, in the space of
mass eigenstates, the two requirements -- of universality for weak diagonal
currents and -- of the absence of their non-diagonal counterparts, although not
fulfilled separately any more, can however reduce to a single condition for a
unique mixing angle theta\_c. This leads to tan (2 theta\_c)=+/- 1/2, or cos
theta\_c \approx 0.9732, only 7/10000 away from experimental results. No mass
ratio appears in the argumentation.Comment: This is a different version of hep-ph/0607193, with a simplified
argumentation, a clearer connection with hep-ph/0606303. The solution for the
Cabibbo angle is also expressed in terms of the golden number. To appear in
Phys. Lett.
Neutrino mixing angles and eigenstates; CP properties and mass hierarchies
In the presence of independent generations of leptons, I show that the same
type of ambiguity in the mass spectrum arises as was discussed in ref.[1] for
neutral kaons. It results from the freedom to add to their Majorana mass
matrix, usually taken to be symmetric, an antisymmetric term which vanishes as
soon as fermions belonging to different generations anticommute. In the simple
examples proposed, dealing with two generations, this procedure introduces an
extra (mass) parameter , which is shown to connect the (CP violating)
mixing angle to the hierarchy of neutrino masses. We use this opportunity to
investigate the relations between the two; in particular, large hierarchies are
no longer preferentially attached to small mixing angles; this can be relevant
for the ``Large Mixing Angle'' solution strongly advocated by recent
experiments on neutrinos oscillations. I discuss how the parameter could
be fixed, which appears, in the absence of a substructure for leptons, still
more delicate than for kaons.Comment: LaTeX 19 pages, 15 postscript figures + 1 Log
The Coupling of the Pion to Two Gauge Fields and to Leptons in a Dynamically Broken Gauge Theory
We show how a spontaneously broken gauge theory of fermions endowed with a
composite scalar multiplet becomes naturally anomaly-free, and yet describes
the correct couplings of the pion to two gauge fields and to leptons: the first
coupling is the same as computed from the chiral anomaly, and the second
identical with that obtained from the `Partially Conserved Axial Current'
hypothesis. For the sake of simplicity, we only study here the abelian case.Comment: 10 pages. Latex file, 5 postscript figures included. Preprint
PAR-LPTHE 93/35. The file for the figures had been badly transmitted. The new
uuencoded compressed tarred file should be now correc
Mixing at 1-loop in a SU(2)_L gauge theory of weak interactions
Flavor mixing is scrutinized at 1-loop in a SU(2)_L gauge theory of massive
fermions. The main issue is to cope with kinetic-like, momentum (p^2) dependent
effective interactions that arise at this order. They spoil the unitarity of
the connection between flavor and mass states, which potentially alters the
standard Cabibbo-Kobayashi-Maskawa (CKM) phenomenology by giving rise, in
particular, to extra flavor changing neutral currents (FCNC). We explore the
conservative requirement that these should be suppressed, which yields
relations between the CKM angles, the fermion and masses, and a
renormalization scale . For two generations, two solutions arise: either
the mixing angle of the fermion pair the closer to degeneracy is close to
maximal while, inversely, the mass and flavor states of the other pair are
quasi-aligned, or mixing angles in both sectors are very small. For three
generations, all mixing angles of neutrinos are predicted to be large
(theta_{23}, close to maximal, is the largest) and the smallness of their mass
differences induces mass-flavor quasi-alignment for all charged leptons. The
hadronic sector differs in that the top quark is twice as heavy as the W. The
situation is, there, bleaker, as all angles come out too large, but,
nevertheless, encouraging, because theta_{12} decreases as the top mass
increases. Whether other super-heavy fermions could drag it down to realistic
values stays an open issue, together with the role of higher order corrections.
The same type of counterterms that turned off the 4th order static corrections
to the quark electric dipole moment are, here too, needed, in particular to
stabilize quantum corrections to mixing angles.Comment: 40 pages, LaTeX, 3 figure
Gauge bosons in an SU(2)right x SU(2)left x G(leptonique) electroweak model
By considering its generalization to composite J=0 mesons proposed in a
previous work [1], I show how and why a chiral extension of the
Glashow-Salam-Weinberg standard model of electroweak interactions calls, there,
for right-handed charged W_R's coupled with g_R = e/cos(theta_W), and the
masses of which are related to the ones of the left-handed W_L's through the
relation M_L^2 + M_R^2 = M_Z^2. The mesonic sector, having vanishing baryonic
and leptonic number, is neutral with respect to the corresponding U(1)
symmetries, making the natural chiral gauge group to be [SU(2)left x
SU(2)right], blind to the presence of extra Z's. The W_R gauge bosons cannot
have been detected in hadronic colliders and can be very elusive in electroweak
processes involving, in particular, pseudoscalar mesons. Present data select
one among two possible extensions for which, in the right sector: - a specific
breaking of universality occurs between families of quarks, which belong to
inequivalent representations of SU(2)right; - the mixing angle is a free
parameter, constrained to be smaller than the Cabibbo angle by the box diagrams
controlling the K_L-K_S mass difference; this also minimizes contributions to
muon -> electron + photon. The relation g_L^2/M_L^2 = g_R^2/M_R^2 implements
left-right symmetry for low energy charged effective weak interactions. For the
sake of simplicity, this study is performed for two generations only.Comment: LaTeX, 18 pages, 4 postscript figures + 1 logo automatically include
Unlocking the Standard Model. I. 1 generation of quarks. Symmetries
A very specific two-Higgs-doublet extension of the Glashow-Salam-Weinberg
model for one generation of quarks is advocated for, in which the two doublets
are parity transformed of each other and both isomorphic to the Higgs doublet
of the Standard Model. The chiral group U(2)_L X U(2)_R gets broken down to
U(1) X U(1)_{em}. In there, the first diagonal U(1) is directly connected to
parity through the U(1)_LX U(1)_R algebra. Both chiral and weak symmetry
breaking can be accounted for, together with their relevant degrees of freedom.
The two Higgs doublets are demonstrated to be in one-to-one correspondence with
bilinear quark operators.Comment: A misprint in eq. (13) has been corrected (h^3 -> h^2
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