29,246 research outputs found
Phenomenology of a light scalar: the dilaton
We make use of the language of non-linear realizations to analyze
electro-weak symmetry breaking scenarios in which a light dilaton emerges from
the breaking of a nearly conformal strong dynamics, and compare the
phenomenology of the dilaton to that of the well motivated light composite
Higgs scenario. We argue that -- in addition to departures in the
decay/production rates into massless gauge bosons mediated by the conformal
anomaly -- characterizing features of the light dilaton scenario (as well as
other scenarios admitting a light CP-even scalar not directly related to the
breaking of the electro-weak symmetry) are off-shell events at high invariant
mass involving two longitudinally polarized vector bosons and a dilaton, and
tree-level flavor violating processes. Accommodating both electro-weak
precision measurements and flavor constraints appears especially challenging in
the ambiguous scenario in which the Higgs and the dilaton fields strongly mix.
We show that warped higgsless models of electro-weak symmetry breaking are
explicit and tractable realizations of this limiting case.
The relation between the naive radion profile often adopted in the study of
holographic realizations of the light dilaton scenario and the actual dynamical
dilaton field is clarified in the Appendix.Comment: 21 page
On a problem of Pillai with k-generalized Fibonacci numbers and powers of 2
For an integer , let be the --generalized Fibonacci sequence which starts with ( terms) and each term afterwards is the sum of the preceding terms. In this paper, we find all integers having at least two presentations as a difference between a --generalized Fibonacci number and a powers of 2 for any fixed . This paper extends previous work from [9] for the case and [6] for the case
Chaos in Robertson-Walker Cosmology
Chaos in Robertson-Walker cosmological models where gravity is coupled to one
or more scalar fields has been studied by a few authors, mostly using numerical
simulations. In this paper we begin a systematic study of the analytical
aspect. We consider one conformally coupled scalar field and, using the fact
that the model is integrable when the field is massless, we show in detail how
homoclinic chaos arises for nonzero masses using a perturbative method.Comment: 16 pages, Tex, no figures. Minor changes have been added. To appear
in Journal of Mathematical Physic
Motor units distribution and recruitment order retrieved from force / M-wave relationship during stimulated contraction
Precision measurement of the rotational energy-level structure of the three-electron molecule He
The term values of all rotational levels of the
He{_2}^+\,X^+\,^2\Sigma_u^+\,(\nu^+=0) ground vibronic state with
rotational quantum number have been determined with an accuracy of
8 x 10 cm ( MHz) by MQDT-assisted Rydberg spectroscopy
of metastable He. Comparison of these term values with term values
recently calculated ab initio by Tung et al. [J. Chem. Phys. 136, 104309
(2012)] reveal discrepancies that rapidly increase with increasing rotational
quantum number and reach values of 0.07 cm ( GHz) at
.Comment: 11 pages, 6 figure
Transport proteins determine drug sensitivity and resistance in a protozoan parasite, Trypanosoma brucei
Drug resistance in pathogenic protozoa is very often caused by changes to the ‘transportome’ of the parasites. In Trypanosoma brucei, several transporters have been implicated in uptake of the main classes of drugs, diamidines and melaminophenyl arsenicals. The resistance mechanism had been thought to be due to loss of a transporter known to carry both types of agents: the aminopurine transporter P2, encoded by the gene TbAT1. However, although loss of P2 activity is well-documented as the cause of resistance to the veterinary diamidine diminazene aceturate (Berenil®), cross-resistance between the human-use arsenical melarsoprol and the diamidine pentamidine (MPXR) is the result of loss of a separate High Affinity Pentamidine Transporter (HAPT1). A genome-wide RNAi library screen for resistance to pentamidine, published in 2012, gave the key to the genetic identity of HAPT1 by linking the phenomenon to a locus that contains the closely related T. brucei aquaglyceroporin genes TbAQP2 and TbAQP3. Further analysis determined that knockdown of only one pore, TbAQP2, produced the MPXR phenotype. TbAQP2 is an unconventional aquaglyceroporin with unique residues in the “selectivity region” of the pore, and it was found that in several MPXR lab strains the WT gene was either absent or replaced by a chimeric protein, recombined with parts of TbAQP3. Importantly, wild-type AQP2 was also absent in field isolates of T. b. gambiense, correlating with the outcome of melarsoprol treatment. Expression of a wild-type copy of TbAQP2 in even the most resistant strain completely reversed MPXR and re-introduced HAPT1 function and transport kinetics. Expression of TbAQP2 in Leishmania mexicana introduced a pentamidine transport activity indistinguishable from HAPT1. Although TbAQP2 has been shown to function as a classical aquaglyceroporin it is now clear that it is also a high affinity drug transporter, HAPT1. We discuss here a possible structural rationale for this remarkable ability
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