2,659 research outputs found
A classical lower bound on the size of a massive neutrino
In this paper, we calculate the size of a massive neutrino in the following
approach. We perform our calculation using its mass, spin, and magnetic moment
through the neutrino-electron interaction, the classical magnetic
dipole-dipole interaction. Thus, our estimate is obtained by mimicking the
low-energy electroweak scattering process -. This leads to
surprisingly accurate result which differs in less than one order of magnitude
of more detailed calculations with one-loop corrections based on the neutrino
charge radius and the - scattering process. The resulting
estimates are flavour-blind and gauge independent by construction. We also find
that our lower bound is below the reported experimental upper bound on the
electron neutrino charged radius. So we obtained a constraining range for the
neutrino size.Comment: 5 pages, 1 figur
Fundamental constraints on two-time physics
We show that generalizations of classical and quantum dynamics with two times
lead to fundamentally constrained evolution. At the level of classical physics,
Newton's second law is extended and exactly integrated in dimensional
space, leading to effective single-time evolution for any initial condition. In
the domain of quantum mechanics, we follow strictly the hypothesis of
probability conservation by extending the Heisenberg picture to unitary
evolution with two times. As a result, the observability of two temporal axes
is constrained by a generalized uncertainty relation involving level spacings,
total duration of the effect and Planck's constant.Comment: 13 pages, 1 figure. This version close to published pape
Second-order Lagrangians admitting a first-order Hamiltonian formalism
Second-order Lagrangian densities admitting a first-order Hamiltonian
formalism are studied; namely, i) for each second-order Lagrangian density on
an arbitrary fibred manifold the Poincar\'e-Cartan form of
which is projectable onto , by using a new notion of regularity
previously introduced, a first-order Hamiltonian formalism is developed for
such a class of variational problems; ii) the existence of first-order
equivalent Lagrangians are discussed from a local point of view as well as
global; iii) this formalism is then applied to classical Einstein-Hilbert
Lagrangian and a generalization of the BF theory. The results suggest that the
class of problems studied is a natural variational setting for GR
The stabilizer group of honeycomb lattices and its application to deformed monolayers
Isospectral transformations of exactly solvable models constitute a fruitful
method for obtaining new structures with prescribed properties. In this paper
we study the stability group of the Dirac algebra in honeycomb lattices
representing graphene or boron nitride. New crystalline arrays with conical
(Dirac) points are obtained; in particular, a model for dichalcogenide
monolayers is proposed and analyzed. In our studies we encounter unitary and
non-unitary transformations. We show that the latter give rise to \mbox{\cal
P\,}\mbox{\cal T\,}-symmetric Hamiltonians, in compliance with known
results in the context of boosted Dirac equations. The results of the unitary
part are applied to the description of invariant bandgaps and dispersion
relations in materials such as MoS. A careful construction based on atomic
orbitals is proposed and the resulting dispersion relation is compared with
previous results obtained through DFT.Comment: 15 pages, 6 figures. This version close to published pape
Diffraction of particles in free fall
The problem of a beam of quantum particles falling through a diffractive
screen is studied. The solutions for single and double slits are obtained
explicitly when the potential is approximated by a linear function. It is found
that the resulting patterns depend on a quasi-time given by a function
of the coordinate along the propagation axis in a classical combination
, while the diffraction effects along transverse axes are due
solely to . The consequences on the precision at which the equivalence
principle can be tested are discussed. Realizations with ultra cold neutrons,
Bose-Einstein condensates and molecular beams are proposed.Comment: This version accepted for publication, Phys Rev A. 12 pages, 5
figures, double colum
General circular velocity relation of a test particle in a 3D gravitational potential: application to the rotation curves analysis and total mass determination of UGC 8490 and UGC 9753
In this paper we derive a novel circular velocity relation for a test
particle in a 3D gravitational potential applicable to every system of
curvilinear coordinates, suitable to be reduced to orthogonal form. As an
illustration of the potentiality of the determined circular velocity expression
we perform the rotation curves analysis of UGC 8490 and UGC 9753 and we
estimate the total and dark matter mass of these two galaxies under the
assumption that their respective dark matter halos have spherical, prolate and
oblate spheroidal mass distributions. We employ stellar population synthesis
models and the total HI density map to obtain the stellar and HI+He+metals
rotation curves of both galaxies. The subtraction of the stellar plus gas
rotation curves from the observed rotation curves of UGC 8490 and UGC 9753
generates the dark matter circular velocity curves of both galaxies. We fit the
dark matter rotation curves of UGC 8490 and UGC 9753 through the newly
established circular velocity formula specialised to the spherical, prolate and
oblate spheroidal mass distributions, considering the Navarro, Frenk and White,
Burkert, Di Cintio, Einasto and Stadel dark matter halos. Our principal
findings are the following: globally, cored dark matter profiles Burkert and
Einasto prevail over cuspy Navarro, Frenk and White and Di Cintio. Also,
spherical/oblate dark matter models fit better the dark matter rotation curves
of both galaxies than prolate dark matter halos.Comment: 23 pages, 16 figures, published in MNRAS Main Journa
Mass content of UGC 6446 and UGC 7524 through HI rotation curves: deriving the stellar discs from stellar population synthesis models
In this work we study the mass distribution of two irregular galaxies, UGC
6446 and UGC 7524, by means of HI rotation curves derived from high resolution
HI velocity fields obtained through the Westerbork Synthesis Radio Telescope
data archive. We constrain the stellar and gas content of both galaxies with
stellar population synthesis models and by deriving the HI+He+metals rotation
curves from the total HI surface density maps, respectively. The discrepancy
between the circular velocity maxima of the stellar plus the HI+He+metals
rotation curves and the observed HI rotation curves of both galaxies requires
the inclusion of a substantial amount of dark matter. We explore the Navarro
Frenk and White, Burkert, Di Cintio, Einasto and Stadel dark matter halo
models. We obtain acceptable fits to the observed HI rotation curves of UGC
6446 and UGC 7524 with the cored Burkert, Einasto and Stadel dark matter halos.
In particular, Einasto and Stadel models prove to be an appropriate alternative
to the Burkert dark matter halo. This result should increase the empirical
basis that justify the usage of dark matter exponential models to adjust the
observed rotation curves of real galaxies.Comment: 18 pages, 16 figures, published in Monthly Notices of the Royal
Astronomical Society, Main Journa
Stern-Gerlach splitters for lattice quasispin
We design a Stern-Gerlach apparatus that separates quasispin components on
the lattice, without the use of external fields. The effect is engineered using
intrinsic parameters, such as hopping amplitudes and on-site potentials. A
theoretical description of the apparatus relying on a generalized
Foldy-Wouthuysen transformation beyond Dirac points is given. Our results are
verified numerically by means of wavepacket evolution, including an analysis of
Zitterbewegung on the lattice. The necessary tools for microwave realizations,
such as complex hopping amplitudes and chiral effects, are simulated.Comment: 10 pages, 11 figures, added closest version to the published one;
corrected typos, formulas and figures rearranged, added appendi
Fabry-Perot Kinematics of HH 202, 203-204 in the Orion Nebula: Are they part of a Big Bipolar Outflow?
We present a kinematic study of the Herbig-Haro objects HH 202, 203 and 204
using Halpha and [NII] Fabry-Perot velocity maps. For HH 202 we find new
features that could belong to this HH object or that perhaps are associated
with an outflow different from HH 202. Because of its high velocity (up to 100
km/seg) this outflow probably can be a HH flow not catalogued previously. Large
internal motions are found in the fainter regions of HH 203-204, as well as
evidence of transverse density gradients. We show that the apex of HH 204 is
the zone of maximum velocity in agreement with bow shock models. From our
studies, we find kinematic evidence that suggests that HH 203-204 and HH 202
are part of a single and large (approx 0.55 pc) HH flow.Comment: 11 pages, 4 figures (in one JPG file). To appear in "Emission Lines
From Jet Flows", Rev. Mex. Astron. and Astrofis. Conf. Se
Disk Mass-to-Light ratio distribution from stellar population synthesis: Application to rotation curve decomposition of NGC 5278 (KPG 390A)
In this work we extend the study on the mass distribution of the spiral
galaxy NGC 5278, performing 1D and 2D bulge-disk decomposition to determine
which components constitute the baryonic mass in this galaxy. Our analysis does
not detect any bulge, instead we find a bright source, probably related with
the central AGN, and an exponential disk. We fix the stellar disk contribution
to the rotation curve (RC) with broad band photometric observations and
population synthesis models, to obtain 2D mass distribution of the stellar
disk. In the particular case of NGC 5278, we find that the typical assumption
of considering the mass-to-luminosity ratio (M/L) of the disk as constant along
the galactocentric radius is not valid. We also extract a baryonic RC from the
mass profile, to determine the inability of this baryonic RC and also of the
baryonic RC with more and less 30% disk mass (in order to consider the disk
mass errors) to fit the entire RC. We perform the RC decomposition of NGC 5278
considering the baryonic RC and four types of dark matter halos: Hernquist;
Burkert; Einasto and Navarro, Frenk & White. Our results show that Hernquist
halo models better our observed RC in the case of determined disk mass
( solar masses) and also with 30% less disk mass. In the
case of 30% more disk mass the cored Einasto (n < 4) halo is the best fitting
model.Comment: 24 pages, 15 figures. Grammar checked. Accepted by Ap
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