120 research outputs found
Trying to understand the Standard Model parameters
We stress the importance of the circa 20 parameters in the Standard Model,
which are not fixed by the model but only determined experimentally, as a
window to the physics beyond the Standard Model. However, it is a tiny window
in as far as these numbers contain only the information corresponding to about
one line of text. Looking for a method to study these coupling and mass
parameters, we put forward the idea of the Multiple Point Principle as a first
step. This principle states that Nature adjusts the coupling and mass
parameters so as to make many different vacuum states exist and have
approximately the same energy densities (cosmological constants). As an
illustrative application, we put up the proposal that a small increase (maybe
only an infinitesimal one) in the value of the top quark coupling constant
could lead to a new vacuum phase; in this new phase the binding of a bound
state of 6 top quarks and 6 anti-top quarks becomes so strong as to become a
tachyon and condense in the vacuum. Assuming the existence of a third
degenerate vacuum at the fundamental energy scale, we present a solution to the
hierarchy problem of why the ratio of the fundamental scale to the electroweak
scale is so large. We also present a 5 parameter fit to the orders of magnitude
of the quark-lepton masses and mixing angles in the Family Replicated Gauge
Group Model. In this model, the Standard Model gauge group and a gauged B-L
(baryon number minus lepton number) is extended to one set of gauge fields for
each family of fermions.Comment: Institute address corrected and one reference adde
Cosmological constant in SUGRA models with Planck scale SUSY breaking and degenerate vacua
The empirical mass of the Higgs boson suggests small to vanishing values of the quartic Higgs self-coupling and the corresponding beta function at the Planck scale, leading to degenerate vacua. This leads us to suggest that the measured value of the cosmological constant can originate from supergravity (SUGRA) models with degenerate vacua. This scenario is realised if there are at least three exactly degenerate vacua. In the first vacuum, associated with the physical one, local supersymmetry (SUSY) is broken near the Planck scale while the breakdown of the SU(2)WĂU(1)Y symmetry takes place at the electroweak (EW) scale. In the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than ÎQCD in the physical vacuum. Finally, in the third vacuum local SUSY and EW symmetry are broken near the Planck scale
Neutrino masses and mixings from an SMG \times U(1)^2 model
A natural solution to the fermion mass hierarchy problem suggests the
existence of a partially conserved chiral symmetry. We show that this can lead
to a reasonably natural solution to the solar and atmospheric neutrino problems
without fine-tuning or the addition of new low energy fermions. The atmospheric
neutrino atmospheric neutrino anomaly is given by large mixing between
and , with \Delta m^2_{atm} \sim 10^{-3} \eV^2, and
the solar neutrino deficit is due to nearly maximal electron neutrino vacuum
oscillations. We present an explicit model for the neutrino masses which is an
anomaly free Abelian extension of the standard model that also yields a
realistic charged fermion spectrum.Comment: 16 pages, 2 figures. Figures use FeynTeX package.Minor modifications
made. Version to appear in Phys.Lett.
Where does Flavour Mixing come from?
We argue that flavour mixing, both in the quark and charged lepton sector, is
basically determined by the lightest family mass generation mechanism. So, in
the chiral symmetry limit when the up and down quark masses vanish, all the
quark mixing angles vanish. This mechanism is not dependent on the number of
quark-lepton families nor on any ``vertical'' symmetry structure, unifying
quarks and leptons inside a family as in Grand Unified Theories. Together with
a hypothesis of maximal CP violation, the model leads to a completely
predictive ansatz for all the CKM matrix elements in terms of the quark masses.
Some implications for neutrino masses and oscillations are briefly discussed.Comment: 13 page LaTeX file, minor changes in fourth paragraph of Conclusion
and in Reference
Lepton Number Violation in Supersymmetric Grand Unified Theories
We argue that the nature of the global conservation laws in Supersymmetric
Grand Unified Theories is determined by the basic vacuum configuration in the
model rather than its Lagrangian. It is shown that the suppression of baryon
number violation in a general (R-parity violating) superpotential can naturally
appear in some extended SU(N) SUSY GUTs which, among other degenerate
symmetry-breaking vacua, have a missing VEV vacuum configuration giving a
solution to the doublet-triplet splitting problem. We construct SU(7) and SU(8)
GUTs where the effective lepton number violating couplings immediately evolve,
while the baryon number non-conserving ones are safely projected out as the GUT
symmetry breaks down to that of the MSSM. However at the next stage, when SUSY
breaks, the radiative corrections shift the missing VEV components to some
nonzero values of order M_{SUSY}, thereby inducing the ordinary Higgs doublet
mass, on the one hand, and tiny baryon number violation, on the other. So, a
missing VEV solution to the gauge hierarchy problem leads at the same time to a
similar hierarchy of baryon vs lepton number violation.Comment: 15 page LaTeX fil
The Origin of Mass
The quark-lepton mass problem and the ideas of mass protection are reviewed.
The hierarchy problem and suggestions for its resolution, including Little
Higgs models, are discussed. The Multiple Point Principle is introduced and
used within the Standard Model to predict the top quark and Higgs particle
masses. Mass matrix ans\"{a}tze are considered; in particular we discuss the
lightest family mass generation model, in which all the quark mixing angles are
successfully expressed in terms of simple expressions involving quark mass
ratios. It is argued that an underlying chiral flavour symmetry is responsible
for the hierarchical texture of the fermion mass matrices. The phenomenology of
neutrino mass matrices is briefly discussed.Comment: 33 pages, 7 figures, to be published in the Proceedings of the XXXI
ITEP Winter School, Moscow, Russia, 18 - 26 February 200
Fermion family recurrences in the Dyson-Schwinger formalism
We study the multiple solutions of the truncated propagator Dyson-Schwinger
equation for a simple fermion theory with Yukawa coupling to a scalar field.
Upon increasing the coupling constant , other parameters being fixed, more
than one non-perturbative solution breaking chiral symmetry becomes possible
and we find these numerically. These ``recurrences'' appear as a mechanism to
generate different fermion generations as quanta of the same fundamental field
in an interacting field theory, without assuming any composite structure. The
number of recurrences or flavors is reduced to a question about the value of
the Yukawa coupling, and has no special profound significance in the Standard
Model. The resulting mass function can have one or more nodes and the
measurement that potentially detects them can be thought of as a collider-based
test of the virtual dispersion relation for the charged
lepton member of each family. This requires three independent measurements of
the charged lepton's energy, three-momentum and off-shellness. We illustrate
how this can be achieved for the (more difficult) case of the tau lepton
Deriving Gauge Symmetry and Spontaneous Lorentz Violation
We consider a class of field theories with a four-vector field
in addition to other fields supplied with a global charge symmetry - theories
which have partial gauge symmetry in the sense of only imposing it on those
terms in the Lagrangian density which have derivatives as factors in them. We
suppose that spontaneous Lorentz invariance breaking occurs in such a theory
due to the four-vector field taking a non-zero vacuum expectation value. Under
some very mild assumptions, we show that this Lorentz violation is not
observable and the whole theory is practically gauge invariant. A very
important presupposition for this theorem is that an initial condition is
imposed on the no-derivative expressions corresponding to the early Universe
being essentially in a vacuum state. This condition then remains true forever
and can be interpreted as a gauge constraint. We formulate the conditions under
which the spontaneous Lorentz violation becomes observable. Spontaneously
broken Lorentz invariance could be seen by some primordially existing or
created "fossil" charges with the property of moving through the Universe with
a fixed velocity.Comment: Extended versio
Minimal Mixing of Quarks and Leptons in the SU(3) Theory of Flavour
We argue that flavour mixing, both in the quark and lepton sector, follows
the minimal mixing pattern, according to which the whole of this mixing is
basically determined by the physical mass generation for the first family of
fermions. So, in the chiral symmetry limit when the masses of the lightest (
and ) quarks vanish, all the quark mixing angles vanish. This minimal
pattern is shown to fit extremely well the already established CKM matrix
elements and to give fairly distinctive predictions for the as yet poorly known
ones. Remarkably, together with generically small quark mixing, it also leads
to large neutrino mixing, provided that neutrino masses appear through the
ordinary ``see-saw'' mechanism. It is natural to think that this minimal
flavour mixing pattern presupposes some underlying family symmetry, treating
families of quarks and leptons in a special way. Indeed, we have found a local
chiral family symmetry model which leads, through its dominant
symmetry breaking vacuum configuration, to a natural realization of the
proposed minimal mechanism. It can also naturally generate the quark and lepton
mass hierarchies. Furthermore spontaneous CP violation is possible, leading to
a maximal CP violating phase , in the framework of the
MSSM extended by a high-scale chiral family symmetry.Comment: 52 pages, LaTex, no figures; some typos corrected; journal versio
Light Higgs Boson in the Spontaneously CP Violating NMSSM
We consider spontaneous CP violation in the Next to Minimal Supersymmetric
Standard Model, without the usual discrete symmetry. CP violation can
occur at tree level, raising a potential conflict with the experimental bounds
on the electric dipole moments of the electron and neutron. One escape from
this is to demand that the CP violating angles are small, but we find that this
entails a light neutral Higgs particle. This is almost pseudoscalar, can have a
high singlet content, and will be hard to detect experimentally.Comment: 14 page LaTeX fil
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