378 research outputs found
Magnus Expansion and Three-Neutrino Oscillations in Matter
We present a semi-analytical derivation of the survival probability of solar
neutrinos in the three generation scheme, based on the Magnus approximation of
the evolution operator of a three level system, and assuming a mass hierarchy
among neutrino mass eigenstates. We have used an exponential profile for the
solar electron density in our approximation. The different interesting density
regions that appear throughout the propagation are analyzed. Finally, some
comments on the allowed regions in the solar neutrino parameter space are
addressed.Comment: RevTex4 style, 5 pages including 5 figures. Presented at Mexican
School of Astrophysics 2002, Guanajuato, Mexico, 31 Jul - 7 Aug 2002. Final
version to appear in the Proceedings of IX Mexican Workshop on Particles and
Fields Physics Beyond the Standard Model, Colima Col. Mexico, November 17-22,
200
Electromagnetic properties of neutrinos
A short review on electromagnetic properties of neutrinos is presented. In
spite of many efforts in the theoretical and experimental studies of neutrino
electromagnetic properties, they still remain one of the main puzzles related
to neutrinos.Comment: The talk presented by A.Studenikin at the International Conference on
Topics in Astroparticle and Underground Physics, Rome (Italy), July 1-5, 200
Protocell Communication Through the Eyes of Synthetic Organic Chemists
The bottom-up fabrication of synthetic cells (protocells) from molecules and materials, is a major challenge of modern chemistry. A significant breakthrough has been the engineering of protocells capable of chemical communication using bio- derived molecules and ex situ stabilised cell machineries. These, however, suffer from short shelf-lives, high costs, and require mild aqueous conditions. In this Concept Article we analyse the chemistry at the heart of protocell communication to highlight new opportunities for synthetic chemists in protocell engineer- ing. Specifically, we (i) categorise the main bio-derived chemical communication machineries in enzyme cascades, DNA strand displacement, and gene-mediated communication; (ii) review the chemistries of these signal transduction machineries; and (iii) introduce new types of bio-inspired, fully synthetic artificial enzymes to replace their natural counterparts. Developing protocells that incorporate synthetic analogues of bio-derived signal transduction machineries will improve the robustness, stability, and versatility of protocells, and broaden their applications to highly strategic fields such as photocatalysis and fine chemicals production
Image-guided multisession radiosurgery of skull base meningiomas
Background: The efficacy of single-session stereotactic radiosurgery (sSRS) for the treatment of intracranial meningioma is widely recognized. However, sSRS is not always feasible in cases of large tumors and those lying close to critically radiation-sensitive structures. When surgery is not recommended, multi-session stereotactic radiosurgery (mSRS) can be applied. Even so, the efficacy and best treatment schedule of mSRS are not yet established. The aim of this study is to validate the role of mSRS in the treatment of skull base meningiomas. Methods: A retrospective analysis of patients with skull base meningiomas treated with mSRS (two to five fractions) at the University of Messina, Italy, from 2008 to 2018, was conducted. Results: 156 patients met the inclusion criteria. The median follow-up period was 36.2 \ub1 29.3 months. Progression-free survival at 2-, 5-, and 10-years was 95%, 90%, and 80.8%, respectively. There were no new visual or motor deficits, nor cranial nerves impairments, excluding trigeminal neuralgia, which was reported by 5.7% of patients. One patient reported carotid occlusion and one developed brain edema. Conclusion: Multisession radiosurgery is an effective approach for skull base meningiomas. The long-term control is comparable to that obtained with conventionally-fractionated radiotherapy, while the toxicity rate is very limited
Treatment of squamous cell carcinoma of the anal canal: A new strategies with anti-EGFR therapy and immunotherapy
The incidence of squamous cell carcinoma of the anal canal (SCAC) is increasing in both sexes but the standard treatment remains that of 20 years ago. However, interesting data have recently emerged on the use of anti-epidermal growth factor receptor (EGFR) agents and immunotherapy in advanced disease. Thus, new avenues of research are opening up that will hopefully lead to more effective therapeutic strategies. We provide an overview of the latest studies published on this tumor and discuss the possible future therapeutic options for combination therapy, anti-EGFR treatment and radiotherapy
General massive one-loop off-shell three-point functions
In this work we compute the most general massive one-loop off-shell
three-point vertex in D-dimensions, where the masses, external momenta, and
exponents of propagators are arbitrary. This follows our previous paper in
which we have calculated several new hypergeometric series representations for
massless and massive (with equal masses) scalar one-loop three-point functions,
in the negative dimensional approach.Comment: 16 pages, 2 figures, 4 table
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
On the thermal footsteps of Neutralino relic gases
Current literature suggests that neutralinos are the dominant cold dark
matter particle species. Assuming the microcanonical definition of entropy, we
examine the local entropy per particle produced between the ``freeze out'' era
to the present. An ``entropy consistency'' criterion emerges by comparing this
entropy with the entropy per particle of actual galactic structures given in
terms of dynamical halo variables. We apply this criterion to the cases when
neutralinos are mosly b-inos and mostly higgsinos, in conjunction with the
usual ``abundance'' criterion requiring that present neutralino relic density
complies with 0.1 < \Omega_{\chic{\tilde\chi^0_1}} < 0.3 for .
The joint application of both criteria reveals that a better fitting occurs for
the b-ino channels, hence the latter seem to be favoured over the higgsino
channels. The suggested methodology can be applied to test other annihilation
channels of the neutralino, as well as other particle candidates of thermal
gases relics.Comment: LaTex AIP style, 8 pages including 1 figure. Final version to appear
in Proceedings of the Mexican School of Astrophysics (EMA), Guanajuato,
M\'exico, July 31 - August 7, 200
Electromagnetic Form Factors of a Massive Neutrino
Electromagnetic form factors of a massive neutrino are studied in a minimally
extended standard model in an arbitrary gauge and taking into account
the dependence on the masses of all interacting particles. The contribution
from all Feynman diagrams to the charge, magnetic, and anapole form factors, in
which the dependence on the masses of all particles as well as on gauge
parameters is accounted for exactly, are obtained for the first time in
explicit form. The asymptotic behavior of the magnetic form factor for large
negative squares of the momentum of an external photon is analyzed and
expression for the anapole moment of a massive neutrino is derived. The results
are generalized to the case of mixing between various generations of the
neutrino. Explicit expressions are obtained for the charge, magnetic, and
electric dipole and anapole transition form factors as well as for the
transition electric dipole moment.Comment: 16 pares with 5 figures in pdf forma
Hydrodynamics of galactic dark matter
We consider simple hydrodynamical models of galactic dark matter in which the
galactic halo is a self-gravitating and self-interacting gas that dominates the
dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static
perfect fluid satisfying the field equations of General Relativity, visible
barionic matter can be treated as ``test particles'' in the geometry of this
field. We show that the assumption of an empirical ``universal rotation curve''
that fits a wide variety of galaxies is compatible, under suitable
approximations, with state variables characteristic of a non-relativistic
Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit.
Consistency criteria lead to a minimal bound for particle masses in the range
and to a constraint between the central
temperature and the particles mass. The allowed mass range includes popular
supersymmetric particle candidates, such as the neutralino, axino and
gravitino, as well as lighter particles ( keV) proposed by numerical
N-body simulations associated with self-interactive CDM and WDM structure
formation theories.Comment: LaTeX article style, 16 pages including three figures. Final version
to appear in Classical and Quantum Gravit
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