4,567 research outputs found
Tri-N-ification
We consider a natural generalization of trinification to theories with 3N
SU(3) gauge groups. These theories have a simple moose representation and a
gauge boson spectrum that can be interpreted via the deconstruction of a 5D
theory with unified symmetry broken on a boundary. Although the matter and
Higgs sectors of the theory have no simple extra-dimensional analog, gauge
unification retains features characteristic of the 5D theory. We determine
possible assignments of the matter and Higgs fields to unified multiplets and
present theories that are viable alternatives to minimal trinified GUTs.Comment: 21 pages LaTeX, 6 eps figure
Clues for the existence of two resonances
The axial vector meson was studied within the chiral unitary
approach, where it was shown that it has a two-pole structure. We reanalyze the
high-statistics WA3 experiment at 63 GeV, which
established the existence of both and , and we show that
it clearly favors our two-pole interpretation. We also reanalyze the
traditional K-matrix interpretation of the WA3 data and find that the good fit
of the data obtained there comes from large cancellations of terms of unclear
physical interpretation.Comment: published version in PRD; typos corrected; title changed to "Clues
for the existence of two resonances
Flavor Changing Scalar Interactions
The smallness of fermion masses and mixing angles has recently been been
attributed to approximate global symmetries, one for each fermion type.
The parameters associated with these symmetry breakings are estimated here
directly from observed masses and mixing angles. It turns out that although
flavor changing reaction rates may be acceptably small in electroweak theories
with several scalar doublets without imposing any special symmetries on the
scalars themselves, such theories generically yield too much CP violation in
the neutral kaon mass matrix. Hence in these theories CP must also be a good
approximate symmetry. Such models provide an alternative mechanism for CP
violation and have various interesting phenomenological features.Comment: 18 pages. UTTG-22-92; LBL 33016; UCB 92/3
A flexible polymer chain in a critical solvent: Coil or globule?
We study the behavior of a flexible polymer chain in the presence of a
low-molecular weight solvent in the vicinity of a liquid-gas critical point
within the framework of a self-consistent field theory. The total free energy
of the dilute polymer solution is expressed as a function of the radius of
gyration of the polymer and the average solvent number density within the
gyration volume at the level of the mean-field approximation. Varying the
strength of attraction between polymer and solvent we show that two
qualitatively different regimes occur at the liquid-gas critical point. In case
of weak polymer-solvent interactions the polymer chain is in a globular state.
On the contrary, in case of strong polymer-solvent interactions the polymer
chain attains an expanded conformation. We discuss the influence of the
critical solvent density fluctuations on the polymer conformation. The reported
effect could be used to excert control on the polymer conformation by changing
the thermodynamic state of the solvent. It could also be helpful to estimate
the solvent density within the gyration volume of the polymer for drug delivery
and molecular imprinting applications
Cell sources for articular cartilage repair strategies: shifting from mono-cultures to co-cultures
The repair of articular cartilage is challenging due to the sparse native cell population combined with the avascular and aneural nature of the tissue. In recent years cartilage tissue engineering has shown great promise. As with all tissue engineering strategies, the possible therapeutic outcome is intimately linked with the used combination of cells, growth factors and biomaterials. However, the optimal combination has remained a controversial topic and no consensus has been reached. In consequence, much effort has been dedicated to further design, investigate and optimize cartilage repair strategies. Specifically, various research groups have performed intensive investigations attempting to identify the single most optimal cell source for articular cartilage repair strategies. However, recent findings indicate that not the heavily investigated mono cell source, but the less studied combinations of cell sources in co-culture might be more attractive for cartilage repair strategies. This review will give a comprehensive overview on the cell sources that have been investigated for articular cartilage repair strategies. In particular, the advantages and disadvantages of investigated cell sources are comprehensively discussed with emphasis on the potential of co-cultures in which benefits are combined while the disadvantages of single cell sources for cartilage repair are mitigated
On the vacuum of the minimal nonsupersymmetric SO(10) unification
We study a class of nonsupersymmetric SO(10) grand unified scenarios where
the first stage of the symmetry breaking is driven by the vacuum expectation
values of the 45-dimensional adjoint representation. Three decade old results
claim that such a Higgs setting may lead exclusively to the flipped SU(5) x
U(1) intermediate stage. We show that this conclusion is actually an artifact
of the tree level potential. The study of the accidental global symmetries
emerging in various limits of the scalar potential offers a simple
understanding of the tree level result and a rationale for the drastic impact
of quantum corrections. We scrutinize in detail the simplest and paradigmatic
case of the 45_{H} + 16_{H} Higgs sector triggering the breaking of SO(10) to
the standard electroweak model. We show that the minimization of the one-loop
effective potential allows for intermediate SU(4)_C x SU(2)_L x U(1)_R and
SU(3)_c x SU(2)_L x SU(2)_R x U(1)_{B-L} symmetric stages as well. These are
the options favoured by gauge unification. Our results, that apply whenever the
SO(10) breaking is triggered by , open the path for hunting the simplest
realistic scenario of nonsupersymmetric SO(10) grand unification.Comment: 22 pages, 1 figure. Refs added. To appear in Phys. Rev.
Yukawa terms in noncommutative SO(10) and E6 GUTs
We propose a method for constructing Yukawa terms for noncommutative SO(10)
and E6 GUTs, when these GUTs are formulated within the enveloping-algebra
formalism. The most general noncommutative Yukawa term that we propose
contains, at first order in thetamunu, the most general BRS invariant Yukawa
contribution whose only dimensionful parameter is the noncommutativity
parameter. This noncommutative Yukawa interaction is thus renormalisable at
first order in thetamunu.Comment: 14 pages, no figure
Asymptotic Freedom: From Paradox to Paradigm
Asymptotic freedom was developed as a response to two paradoxes: the
weirdness of quarks, and in particular their failure to radiate copiously when
struck; and the coexistence of special relativity and quantum theory, despite
the apparent singularity of quantum field theory. It resolved these paradoxes,
and catalyzed the development of several modern paradigms: the hard reality of
quarks and gluons, the origin of mass from energy, the simplicity of the early
universe, and the power of symmetry as a guide to physical law.Comment: 26 pages, 10 figures. Lecture on receipt of the 2004 Nobel Prize. v2:
typo (in Ohm's law) correcte
Constraining the Littlest Higgs
Little Higgs models offer a new way to address the hierarchy problem, and
give rise to a weakly-coupled Higgs sector. These theories predict the
existence of new states which are necessary to cancel the quadratic divergences
of the Standard Model. The simplest version of these models, the Littlest
Higgs, is based on an non-linear sigma model and predicts that
four new gauge bosons, a weak isosinglet quark, , with , as well as
an isotriplet scalar field exist at the TeV scale. We consider the
contributions of these new states to precision electroweak observables, and
examine their production at the Tevatron. We thoroughly explore the parameter
space of this model and find that small regions are allowed by the precision
data where the model parameters take on their natural values. These regions
are, however, excluded by the Tevatron data. Combined, the direct and indirect
effects of these new states constrain the `decay constant' f\gsim 3.5 TeV and
m_{t'}\gsim 7 TeV. These bounds imply that significant fine-tuning be
present in order for this model to resolve the hierarchy problem.Comment: 31 pgs, 26 figures; bound on t' mass fixed to mt'>2f, conclusions
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