3,710 research outputs found
Relativistic kinematics beyond Special Relativity
In the context of departures from Special Relativity written as a momentum
power expansion in the inverse of an ultraviolet energy scale M, we derive the
constraints that the relativity principle imposes between coefficients of a
deformed composition law, dispersion relation, and transformation laws, at
first order in the power expansion. In particular, we find that, at that order,
the consistency of a modification of the energy-momentum composition law fixes
the modification in the dispersion relation. We therefore obtain the most
generic modification of Special Relativity that preserves the relativity
principle at leading order in 1/M.Comment: Version with minor corrections, to appear in Phys. Rev.
Tachoastrometry: astrometry with radial velocities
Spectra of composite systems (e.g., spectroscopic binaries) contain spatial
information that can be retrieved by measuring the radial velocities (i.e.,
Doppler shifts) of the components in four observations with the slit rotated by
90 degrees in the sky. By using basic concepts of slit spectroscopy we show
that the geometry of composite systems can be reliably retrieved by measuring
only radial velocity differences taken with different slit angles. The spatial
resolution is determined by the precision with which differential radial
velocities can be measured. We use the UVES spectrograph at the VLT to observe
the known spectroscopic binary star HD 188088 (HIP 97944), which has a maximum
expected separation of 23 milli-arcseconds. We measure an astrometric signal in
radial velocity of 276 \ms, which corresponds to a separation between the two
components at the time of the observations of 18 milli-arcseconds. The
stars were aligned east-west. We describe a simple optical device to
simultaneously record pairs of spectra rotated by 180 degrees, thus reducing
systematic effects. We compute and provide the function expressing the shift of
the centroid of a seeing-limited image in the presence of a narrow slit.The
proposed technique is simple to use and our test shows that it is amenable for
deriving astrometry with milli-arcsecond accuracy or better, beyond the
diffraction limit of the telescope. The technique can be further improved by
using simple devices to simultaneously record the spectra with 180 degrees
angles.With tachoastrometry, radial velocities and astrometric positions can be
measured simultaneously for many double line system binaries in an easy way.
The method is not limited to binary stars, but can be applied to any
astrophysical configuration in which spectral lines are generated by separate
(non-rotational symmetric) regions.Comment: Accepted for publication in A&
Bound states in the continuum: localization of Dirac-like fermions
We report the formation of bound states in the continuum for Dirac-like
fermions in structures composed by a trilayer graphene flake connected to
nanoribbon leads. The existence of this kind of localized states can be proved
by combining local density of states and electronic conductance calculations.
By applying a gate voltage, the bound states couple to the continuum, yielding
a maximum in the electronic transmission. This feature can be exploited to
identify bound states in the continuum in graphene-based structures.Comment: 7 pages, 5 figure
Light-cone quantization of two dimensional field theory in the path integral approach
A quantization condition due to the boundary conditions and the
compatification of the light cone space-time coordinate is identified at
the level of the classical equations for the right-handed fermionic field in
two dimensions. A detailed analysis of the implications of the implementation
of this quantization condition at the quantum level is presented. In the case
of the Thirring model one has selection rules on the excitations as a function
of the coupling and in the case of the Schwinger model a double integer
structure of the vacuum is derived in the light-cone frame. Two different
quantized chiral Schwinger models are found, one of them without a
-vacuum structure. A generalization of the quantization condition to
theories with several fermionic fields and to higher dimensions is presented.Comment: revtex, 14 p
Adsorption Mechanism and Uptake of Methane in Covalent Organic Frameworks: Theory and Experiment
We determined the methane (CH_4) uptake (at 298 K and 1 to 100 bar pressure) for a variety of covalent organic frameworks (COFs), including both two-dimensional (COF-1, COF-5, COF-6, COF-8, and COF-10) and three-dimensional (COF-102, COF-103, COF-105, and COF-108) systems. For all COFs, the CH_4 uptake was predicted from grand canonical Monte Carlo (GCMC) simulations based on force fields (FF) developed to fit accurate quantum mechanics (QM) [second order Møller−Plesset (MP2) perturbation theory using doubly polarized quadruple-ζ (QZVPP) basis sets]. This FF was validated by comparison with the equation of state for CH_4 and by comparison with the experimental uptake isotherms at 298 K (reported here for COF-5 and COF-8), which agrees well (within 2% for 1−100 bar) with the GCMC simulations. From our simulations we have been able to observe, for the first time, multilayer formation coexisting with a pore filling mechanism. The best COF in terms of total volume of CH_4 per unit volume COF absorbent is COF-1, which can store 195 v/v at 298 K and 30 bar, exceeding the U.S. Department of Energy target for CH_4 storage of 180 v/v at 298 K and 35 bar. The best COFs on a delivery amount basis (volume adsorbed from 5 to 100 bar) are COF-102 and COF-103 with values of 230 and 234 v(STP: 298 K, 1.01 bar)/v, respectively, making these promising materials for practical methane storage
Conserved Ising Model on the Human Connectome
Dynamical models implemented on the large scale architecture of the human
brain may shed light on how function arises from the underlying structure. This
is the case notably for simple abstract models, such as the Ising model. We
compare the spin correlations of the Ising model and the empirical functional
brain correlations, both at the single link level and at the modular level, and
show that their match increases at the modular level in anesthesia, in line
with recent results and theories. Moreover, we show that at the peak of the
specific heat (the \it{critical state}) the spin correlations are minimally
shaped by the underlying structural network, explaining how the best match
between structure and function is obtained at the onset of criticality, as
previously observed. These findings confirm that brain dynamics under
anesthesia shows a departure from criticality and could open the way to novel
perspectives when the conserved magnetization is interpreted in terms of an
homeostatic principle imposed to neural activity
Asymptotic approach to Special Relativity compatible with a relativistic principle
We propose a general framework to describe Planckian deviations from Special
Relativity (SR) compatible with a relativistic principle. They are introduced
as the leading corrections in an asymptotic approach to SR going beyond the
energy power expansion of effective field theories. We discuss the conditions
in which these Planckian effects might be experimentally observable in the near
future, together with the non-trivial limits of applicability of this
asymptotic approach that such a situation would produce, both at the very high
(ultraviolet) and the very low (infrared) energy regimes.Comment: 12 page
Special Geometry of Euclidean Supersymmetry III: the local r-map, instantons and black holes
We define and study projective special para-Kahler manifolds and show that
they appear as target manifolds when reducing five-dimensional vector
multiplets coupled to supergravity with respect to time. The dimensional
reductions with respect to time and space are carried out in a uniform way
using an epsilon-complex notation. We explain the relation of our formalism to
other formalisms of special geometry used in the literature. In the second part
of the paper we investigate instanton solutions and their dimensional lifting
to black holes. We show that the instanton action, which can be defined after
dualising axions into tensor fields, agrees with the ADM mass of the
corresponding black hole. The relation between actions via Wick rotation, Hodge
dualisation and analytic continuation of axions is discussed.Comment: 72 pages, 2 figure
Consistency of Lorentz-invariance violation neutrino scenarios in time delay analyses
Modifications inspired by quantum gravity in the kinematics of special
relativity can manifest in various ways, including anomalies in the time of
flight of massless particles and the emergence of decay channels for otherwise
stable particles. Typically, these effects are studied independently; however,
it may be necessary to combine both to perform a consistent analysis. In this
work, we study the interplay between time-of-flight anomalies and neutrino
instability in the context of a flavor-independent high-energy
Lorentz-invariance violation (LIV) in the neutrino sector. Ensuring
compatibility between both types of effects imposes strong constraints on the
existence of early neutrinos with energies exceeding a maximum value determined
by the scale of new physics. Such constraints depend on the specific LIV
scenario and should be integrated into searches for high-energy neutrinos from
gamma-ray bursts exhibiting LIV time shifts.Comment: 14 pages, 6 figure
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