LF11407
Novel Macroscopic Force Mediated by Unparticles
An object called `unparticle¡¯ could exert a macroscopic force between
ordinary matter. It differs sharply from the only known macroscopic forces
in Nature, electromagnetic and gravitational: It does not follow the Inverse
Square Law; it is even a non-integral power of distance! The known
macroscopic forces are mediated by certain force carrier, a particle of zero
mass, which results in the Inverse Square Law in our physical space. The
notion of unparticle, as suggested recently by the particle theorist
H. Georgi, is something different from a particle. Mass is no more a
property that characterizes it; instead, a number called scaling dimension
dictates how it behaves when time and space shrink or enlarge proportionally.
We show in our paper how this new property leads to the unusual force between
matter when unparticles interact with particles. Since such a force cannot
appear in a theory of particles, if discovered, it would be an importance
advance in physics and would modify our conceptual framework based on
particles. Conversely, null observation of it would restrict unparticle-
particle interactions, if existing at all, to be very weak.
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lf11644
Quantum-Chromo-Dynamics is an accepted theory of strong interactions. The
elementary objects of the theory are almost massless U and D quarks and
massless gluons. Ultimately it must explain masses and other properties
of all strongly interacting particles such as proton, neutron and their
excitations. The theory has a symmetry called chiral symmetry. It is
firmly established that this symmetry is spontaneously broken in the
vacuum. It was believed that for the mass generation mechanism of hadrons
consisting of U and D quarks spontaneous breaking of chiral symmetry in
the vacuum is crucially important. In the present as well as in the
previous papers of the author it is suggested that generally it is not
the case: in the (highly) excited hadrons the mass generation mechanism is
not related with the spontaneous breaking of chiral symmetry in the vacuum
and the chiral symmetry can be approximately restored in these excited hadrons.
The chiral symmetry restoration in the given hadron requires this hadron to
decouple from the Goldstone bosons (particles which necessarily accompany
spontaneous breaking of the symmetry). It is shown in the present paper that
existing for many years experimental data on strong decays of excited protons and
neutrons do support chiral symmetry restoration in excited hadrons.
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LF11481
Surprise for Bose-Einstein condensation in semiconductors: Excitons condense dark
Excitons are semiconductor excitations made of conduction electrons and valence holes
bound in hydrogenlike bosonic atoms. They should thus display Bose-Einstein condensation
(BEC). However, for tens of years, claims of observation have been followed by denials,
probably because of the condensate unexpected nature.
Excitons resulting from photon absorption are created « bright » (coupled to light)
However, as fermion exchanges scatter bright excitons with opposite spins into « dark
states, photoexcited semiconductors ultimately contain bright and dark excitons.
Since dark excitons have the lowest energy - for they do not have interband (repulsive)
Coulomb processes due to spin incompatibility - the exciton condensate, made of the
lowest energy state, has thus to be dark. Through the Shiva diagram representation of
the new composite boson many-body theory, it is then easy to show that the coupling
between dark and bright excitons forces the condensed state to be linearly polarized
- to minimize the energy.
This new light on exciton BEC came because of rejecting the well accepted idea that
excitons behave as elementary bosons interacting through effective scatterings, idea
the new theory shows incorrect for many-body effects - essentially driven by fermion
exchanges without fermion interaction.
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LF11505
CONDUCTION ELECTRONS IN GRAPHITE FLOW ALMOST WITHOUT RESISTANCE
Graphite - the well-known stack of fairly uncoupled graphene planes - shows amazing transport properties, which are being revealed nowadays after decades of experimental and theoretical studies. Similar to light diffraction the bending of conduction electrons by scattering obstacles that define the electronic mean free path in a metal, is effective only if the obstacles size is comparable to the electron de Broglie wavelength. The conduction electrons in graphite have such a large wavelength that usual scattering centres are rather ineffective to affect their transport properties providing a mean free path of several micrometers, even at room temperature. A direct way to “see” this is presented in this letter where it shows that the ordinary change of resistance with magnetic field is affected by macroscopically large sample sizes. The presented evidence suggests that graphite may provide the unusual possibility to study electron optics in a solid but also that superconducting-like paths even at room temperature may exist. These are the good news. And the bad news? Well, it depends on the reader point of view. Solid state physicists may realize now that the semiclassical transport models used in graphite in the last 50 years and also recently in graphene are actually not applicable and a general revision of the experimental and theoretical work is required.
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LF11659
Diffusion Towards a Fractal Absorber
We expect the result of a simple medical test after a day or so, and wait for a few more days if the tests are complicated. Future tests involving personalized medicine ( e.g., sequencing the genome of a person) might take considerably longer, making them expensive and -- if the delay is too long – the results are practically useless. To speed things up, one could put many sensors in parallel and/or make each sensor more responsive. Unfortunately, despite considerable effort, our understanding of the physical limits of response time of a bio sensor is still evolving.
In a soon-to-be-published article in PRL, we show that it is the shape of a sensor that dictates the "geometry of diffusion" of the target particles around it and in the process, self-establishes its minimum response time. Indeed, the shape of a sensor and its response time are related by a simple scaling relationship that holds true even for complex surfaces defined only by its fractal dimension and the corresponding 'dimensionally frustrated' diffusion (of target particles) characterized by periodic flipping of between 1D and 2D diffusion profiles.
The concept that 'form dictates function' is hardly new: In 1960s, Mark Kac asked "Can one hear the shape of a drum?" exploring relationship between shape an object and the acoustic wave created by it. The PRL article provides a new example of such relationship that relates the shape of an object to the diffusion field towards it – and in doing so broadens the range of problems accessible through the so-called "diffusion-limited aggression".
***LH10911
Measuring complex flows by Nuclear Magnetic Resonance
When blood is pumped through the brain, the tortuous capillary pathways result in a complex, fluctuating flow. A new Nuclear Magnetic Resonance (NMR) method has just been developed which may unravel some of that complexity. And given that NMR underpins the medical imaging technology, MRI, the potential for human application is significant.
Beyond blood perfusion in the brain, complex flow lies at the heart of other medical processes such as respiration or human cell division, industrial processes like oil recovery or the behavior of packed bed chemical reactors, and environmental processes such as ground water remediation and purification by filtration. Any tool which assists better understanding of such flow is therefore of interest.
At the heart of that understanding is being able to connect fluctuations in fluid velocities displaced in position and time. The new NMR method measures, for the first time, the fundamental quantity in the mathematical description, namely the “non-local dispersion tensor”. First proposed by Caltech scientists Donald Koch and John Brady in 1987, this tensor, which contains the vital information about fluid space-time correlations, has until now, been unmeasurable. This new breakthrough involving NMR not only gives a new boost to the mathematical theory of complex flow, but also holds promise for use as a contrast in medical imaging.
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LG11648
Quantum Nonlocality of the Original EPR State via Spatial Parity
Entanglement
For the first time since it was proposed more than 70 years ago, the
nonlocal character of the original Einstein--Podolsky--Rosen (EPR) state
has been exposed via an experiment on two photons that are perfectly
entangled in their positions (implying that measuring the position of
one particle reveals the position of the other). The experiment reveals
a definitive violation of Bell⿿s inequality, the hallmark of
nonlocality. While entangled states have been used to show the violation
using other degrees of freedom, the spatial degree of freedom has
remained elusive even though it was the parameter that EPR used to cast
their thought experiment. Most prior work focused on measuring the
positions of each particle, but the key variable turns out to be their
spatial parities, a binary property that is mathematically analogous to
polarization. Spatial parity rotation, the operation analogous to
polarization rotation, is achieved by the introduction of a relative
phase between positive and negative positions. Einstein and his
colleagues might have been disappointed to learn that quantum mechanics
does indeed allow for nonlocality, which they called ⿿spooky action at a
distance, but they might also have taken pleasure in the discovery of
parity entanglement.
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LE11549
Suppression of the Anderson localization by metamaterials A theory of diluted white paint?
Localization, one of most fundamental characteristics of disordered materials, refers to the extinguishment of propagation due to strong scattering that is induced by disorder. Indeed, this the mechanism that makes white paint actually “white”, as discussed in P. W. Anderson’s famous article "The question of classical localization A theory of white paint? in Philosophical Magazine B, 52, 505 (1985). In our Letter, we show that the introduction of metamaterials—novel, manufactured materials having the property of negative refraction—when mixed with normal materials, are able to substantially suppress the localization of photons. In particular, the localization length (the characteristic distance of the exponent decay of the field) exhibits a markedly different behavior in the long wavelength spectrum behaving as the sixth power of the wavelength, rather than the square of the wavelength for regular, right-handed materials. This demonstrates a substantial suppression of loc
alization, and hence the disordered material will appear less “white” and more transparent at these wavelengths. Furthermore, these mixed structures, which incorporate both normal and metamaterials show much weaker transmission resonances at long wavelengths, due to the inclusion of negative phase materials which weaken scattering. Such properties are quite surprising and deserve further investigation that can lead to new insights into localization, even for normal materials.
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LE10899
Nonlocality of a single particle
This Letter presents an exciting new scheme that could resolve the long-running debate over the fundamental issue of whether a single particle can exhibit nonlocality. This is a very important issue in science since quantum field theory is the most fundamental description of nature and, in this theory, excitations rather than particles are the most fundamental entities. If nonlocality only existed when we had two or more particles, this would present a serious problem, since there would suddenly be something peculiar about two excitations of the field that would not exist when we had only one.
Single-photon nonlocality has been hotly-debated ever since it was first suggested in 1991. So far, the schemes proposed to test this idea have been criticised as not representing real experiments. This Letter resolves the issue by presenting a simple scheme that is achievable in the laboratory with current technology. This scheme is particularly exciting because it applies to atoms as well as photons and could overturn the widespread view that superselection rules prevent us from observing the nonlocality of a single massive particle.
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LD11381
Photonic crystal fiber enhances the efficiency and directionality of random laser action in highly scattering medium
Directional and efficient random laser emission was obtained by placing a highly scattering gain medium in the hollow core of a photonic crystal fiber (PCF). In conventional lasers, photons (i.e. light particles) are initially emitted at random within an amplifying medium. Mirrors placed at the medium’s edges make a few of these bounce back, inducing the emission of new photons in an avalanche-like process. In random lasers, which have been investigated for over a decade, the amplifying medium is highly scattering and emitted photons randomly bounce several times at the scatterers before leaving the medium. This random movement also generates amplification and laser-like emission. Because all photons, and not just those collected by external mirrors, are amplified, the threshold behavior in random lasers is much smoother, a characteristic that leans toward the long sought ideal of a thresholdless laser. However, the emission shows no directionality, which hinders some applications of random lasers as practical sources. In this paper, by inserting the random laser medium in the PCF core, a reasonable fraction of emitted and randomly scattered photons experience total internal reflection on the core boundaries and become guided, leading to a directional laser-like source. In addition, these reflections make photons spend more time in the gain medium, resulting in a device efficiency that is at least 100 times higher than those observed in similar systems in bulk format.
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LE11563
A relativistic thermometer for Einstein
The unification of thermodynamics and special relativity
poses a long-standing, fundamental problem which continues
to haunt the physics literature. In this paper, we present
novel fully relativistic molecular dynamics simulations that
shed light on this challenging topic. Our numerical results
illustrate that a statistical thermometer can be devised
which is able to measure the temperature of relativistic
many-particle systems in a Lorentz-invariant way.
This implies important practical consequences:
A moving observer, who passes by a resting gas container,
measures the same temperature as a resting observer.
Thus, in contrast to previous, repeated claims,
moving bodies appear neither hotter nor colder.
