3,054 research outputs found
A SINFONI view of Galaxy Centers: Morphology and Kinematics of five Nuclear Star Formation Rings
We present near-infrared (H- and K-band) integral-field observations of the
circumnuclear star formation rings in five nearby spiral galaxies. The data,
obtained at the Very Large Telescope with the SINFONI spectrograph, are used to
construct maps of various emission lines that reveal the individual star
forming regions ("hot spots") delineating the rings. We derive the
morphological parameters of the rings, and construct velocity fields of the
stars and the emission line gas. We propose a qualitative, but robust,
diagnostic for relative hot spot ages based on the intensity ratios of the
emission lines Brackett gamma, HeI, and [FeII]. Application of this diagnostic
to the data presented here provides tentative support for a scenario in which
star formation in the rings is triggered predominantly at two well-defined
regions close to, and downstream from, the intersection of dust lanes along the
bar with the inner Lindblad resonance.Comment: 45 pages incl. 4 tables and 12 (mostly color) figures. Accepted for
publication in AJ. A version with full resolution figures can be obtained at
ftp://ftp.rssd.esa.int/pub/tboeker/SINFONI/ms.pd
Ballistic transport, chiral anomaly and emergence of the neutral electron - hole plasma in graphene
The process of coherent creation of particle - hole excitations by an
electric field in graphene is quantitatively described using a dynamic "first
quantized" approach. We calculate the evolution of current density, number of
pairs and energy in ballistic regime using the tight binding model. The series
in electric field strength up to third order in both DC and AC are
calculated. We show how the physics far from the two Dirac points enters
various physical quantities in linear response and how it is related to the
chiral anomaly. The third harmonic generation and the imaginary part of
conductivity are obtained. It is shown that at certain time scale
the physical behaviour dramatically changes and the
perturbation theory breaks down. Beyond the linear response physics is explored
using an exact solution of the first quantized equations. While for small
electric fields the I-V curve is linear characterized by the universal minimal
resistivity %, at the conductivity grows
fast. The copious pair creation (with rate ), analogous to Schwinger's
electron - positron pair creation from vacuum in QED, leads to creation of the
electron - hole plasma at ballistic times of order . This process is
terminated by a relaxational recombination.Comment: 15 pages, 5 figures
Weak-localization and rectification current in non-diffusive quantum wires
We show that electron transport in disordered quantum wires can be described
by a modified Cooperon equation, which coincides in form with the Dirac
equation for the massive fermions in a 1+1 dimensional system. In this new
formalism, we calculate the DC electric current induced by electromagnetic
fields in quasi-one-dimensional rings. This current changes sign, from
diamagnetic to paramagnetic, depending on the amplitude and frequency of the
time-dependent external electromagnetic field.Comment: changed title, added more detail, to appear in J. Phys.: Condens.
Matte
Dark matter: A spin one half fermion field with mass dimension one?
We report an unexpected theoretical discovery of a spin one half matter field
with mass dimension one. It is based on a complete set of eigenspinors of the
charge conjugation operator. Due to its unusual properties with respect to
charge conjugation and parity it belongs to a non standard Wigner class.
Consequently, the theory exhibits non-locality with (CPT)^2 = - I. Its dominant
interaction with known forms of matter is via Higgs, and with gravity. This
aspect leads us to contemplate it as a first-principle candidate for dark
matter.Comment: 5 pages, RevTex, v2: slightly extended discussion, new refs. and note
adde
Equivalence between different classical treatments of the O(N) nonlinear sigma model and their functional Schrodinger equations
In this work we derive the Hamiltonian formalism of the O(N) non-linear sigma
model in its original version as a second-class constrained field theory and
then as a first-class constrained field theory. We treat the model as a
second-class constrained field theory by two different methods: the
unconstrained and the Dirac second-class formalisms. We show that the
Hamiltonians for all these versions of the model are equivalent. Then, for a
particular factor-ordering choice, we write the functional Schrodinger equation
for each derived Hamiltonian. We show that they are all identical which
justifies our factor-ordering choice and opens the way for a future
quantization of the model via the functional Schrodinger representation.Comment: Revtex version, 17 pages, substantial change
A Chiral Schwinger model, its Constraint Structure and Applications to its Quantization
The Jackiw-Rajaraman version of the chiral Schwinger model is studied as a
function of the renormalization parameter. The constraints are obtained and
they are used to carry out canonical quantization of the model by means of
Dirac brackets. By introducing an additional scalar field, it is shown that the
model can be made gauge invariant. The gauge invariant model is quantized by
establishing a pair of gauge fixing constraints in order that the method of
Dirac can be used.Comment: 18 page
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Saving old bones: A non-destructive method for bone collagen prescreening
Bone collagen is an important material for radiocarbon, paleodietary, and paleoproteomic analyses, but it degrades over time, making such analyses more difficult with older material. Collagen preservation between and within archaeological sites is also variable, so that much time, effort, and money can go into the preparation and initial analysis of samples that will not yield meaningful results. To avoid this, various methods are employed to prescreen bone for collagen preservation (e.g., %N, microporosity, and FTIR spectroscopic analyses), but these are often destructive and/or require exportation for analysis. Here, we explore near-infrared spectroscopy as a tool for gauging the collagen content of ground and whole bone from about 500 to 45,000 years ago. We show that a portable spectrometer’s ability to quantify collagen content and classify specimens by preservation status is comparable to that of other popular prescreening methods. Moreover, near-infrared spectroscopy is non-destructive and spectra can be acquired in a few seconds
Semiquantum Chaos in the Double-Well
The new phenomenon of semiquantum chaos is analyzed in a classically regular
double-well oscillator model. Here it arises from a doubling of the number of
effectively classical degrees of freedom, which are nonlinearly coupled in a
Gaussian variational approximation (TDHF) to full quantum mechanics. The
resulting first-order nondissipative autonomous flow system shows energy
dependent transitions between regular behavior and semiquantum chaos, which we
monitor by Poincar\'e sections and a suitable frequency correlation function
related to the density matrix. We discuss the general importance of this new
form of deterministic chaos and point out the necessity to study open
(dissipative) quantum systems, in order to observe it experimentally.Comment: LaTeX, 25 pages plus 7 postscript figures. Replaced figure 3 with a
non-bitmapped versio
Relativistic echo dynamics and the stability of a beam of Landau electrons
We extend the concepts of echo dynamics and fidelity decay to relativistic
quantum mechanics, specifically in the context of Klein-Gordon and Dirac
equations under external electromagnetic fields. In both cases we define
similar expressions for the fidelity amplitude under perturbations of these
fields, and a covariant version of the echo operator. Transformation properties
under the Lorentz group are established. An alternate expression for fidelity
is given in the Dirac case in terms of a 4-current. As an application we study
a beam of Landau electrons perturbed by field inhomogeneities.Comment: 8 pages, no figure
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