458 research outputs found
On the spin of gravitational bosons
We unearth spacetime structure of massive vector bosons, gravitinos, and
gravitons. While the curvatures associated with these particles carry a
definite spin, the underlying potentials cannot be, and should not be,
interpreted as single spin objects. For instance, we predict that a spin
measurement in the rest frame of a massive gravitino will yield the result 3/2
with probability one half, and 1/2 with probability one half. The simplest
scenario leaves the Riemannian curvature unaltered; thus avoiding conflicts
with classical tests of the theory of general relativity. However, the quantum
structure acquires additional contributions to the propagators, and it gives
rise to additional phases.Comment: Honorable mention, 2002 Gravity Research Foundation Essay
Spin half fermions with mass dimension one: theory, phenomenology, and dark matter
We provide the first details on the unexpected theoretical discovery of a
spin-one-half matter field with mass dimension one. It is based upon a complete
set of dual-helicity 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. We briefly discuss its relevance to the
cosmological `horizon problem'. Because the introduced fermionic field is
endowed with mass dimension one, it can carry a quartic self-interaction. Its
dominant interaction with known forms of matter is via Higgs, and with gravity.
This aspect leads us to contemplate the new fermion as a prime dark matter
candidate. Taking this suggestion seriously we study a supernova-like explosion
of a galactic-mass dark matter cloud to set limits on the mass of the new
particle and present a calculation on relic abundance to constrain the relevant
cross-section. The analysis favours light mass (roughly 20 MeV) and relevant
cross-section of about 2 pb. Similarities and differences with the WIMP and
mirror matter proposals for dark matter are enumerated. In a critique of the
theory we bare a hint on non-commutative aspects of spacetime, and
energy-momentum space.Comment: 78 pages [Changes: referee-suggested improvements, additional
important references, and better readability
Neutrino mixing schemes and neutrinoless double beta decay
We study the possible structure of the neutrino mass matrix taking into
consideration the solar and atmospheric neutrinos and the neutrinoless double
beta decay. We emphasize on mass matrices with vanishing elements. There are
only a very few possibilities remaining at present. We concentrate on three
generation scenarios and find that with three parameters there are few
possibilities with and without any vanishing elements. For completeness we also
present a five parameter four neutrino (with one sterile neutrino) mass matrix
which can explain all these experiments and the LSND result.Comment: 12 pages late
Chalcogen Height Dependence of Magnetism and Fermiology in FeTe_xSe_{1-x}
FeTexSe1-x (x=0, 0.25, 0.50, 0.75 and 1) system has been studied using
density functional theory. Our results show that for FeSe, LDA seems better
approximation in terms of magnitude of magnetic energy whereas GGA
overestimates it largely. On the other hand for FeTe, GGA is better
approximation that gives experimentally observed magnetic state. It has been
shown that the height of chalcogen atoms above Fe layers has significant effect
on band structure, electronic density of states (DOS) at Fermi level N(EF) and
Fermi surfaces. For FeSe the value of N(EF) is small so as to satisfy Stoner
criteria for ferromagnetism, (I\timesN(EF)\geq1) whereas for FeTe, since the
value of N(EF) is large, the same is close to be satisfied. Force minimization
done for FeTexSe1-x using supercell approach shows that in disordered system Se
and Te do not share same site and have two distinct z coordinates. This has
small effect on magnetic energy but no significant difference in band structure
and DOS near EF when calculated using either relaxed or average value of z for
chalcogen atoms. Thus substitution of Se at Te site decreases average value of
chalcogen height above Fe layers which in turn affect the magnetism and
Fermiology in the system. By using coherent-potential approximation for
disordered system we found that height of chalcogen atoms above Fe layer rather
than chalcogen species or disorder in the anion planes, affect magnetism and
shape of Fermi surfaces (FS), thus significantly altering nesting conditions,
which govern antiferromagnetic spin fluctuations in the system.Comment: 24 pages Text+Figs: comments/suggestions welcome
([email protected]
From Hours to Seconds: Towards 100x Faster Quantitative Phase Imaging via Differentiable Microscopy
With applications ranging from metabolomics to histopathology, quantitative
phase microscopy (QPM) is a powerful label-free imaging modality. Despite
significant advances in fast multiplexed imaging sensors and
deep-learning-based inverse solvers, the throughput of QPM is currently limited
by the speed of electronic hardware. Complementarily, to improve throughput
further, here we propose to acquire images in a compressed form such that more
information can be transferred beyond the existing electronic hardware
bottleneck. To this end, we present a learnable optical
compression-decompression framework that learns content-specific features. The
proposed differentiable quantitative phase microscopy () first
uses learnable optical feature extractors as image compressors. The intensity
representation produced by these networks is then captured by the imaging
sensor. Finally, a reconstruction network running on electronic hardware
decompresses the QPM images. In numerical experiments, the proposed system
achieves compression of 64 while maintaining the SSIM of
and PSNR of dB on cells. The results demonstrated by our experiments
open up a new pathway for achieving end-to-end optimized (i.e., optics and
electronic) compact QPM systems that may provide unprecedented throughput
improvements
Does Quantum Mechanics Clash with the Equivalence Principle - and Does it Matter?
With an eye on developing a quantum theory of gravity, many physicists have
recently searched for quantum challenges to the equivalence principle of
general relativity. However, as historians and philosophers of science are well
aware, the principle of equivalence is not so clear. When clarified, we think
quantum tests of the equivalence principle won't yield much. The problem is
that the clash/not-clash is either already evident or guaranteed not to exist.
Nonetheless, this work does help teach us what it means for a theory to be
geometric.Comment: 12 page
Model for Glass Transition in a Binary fluid from a Mode Coupling approach
We consider the Mode Coupling Theory (MCT) of Glass transition for a Binary
fluid. The Equations of Nonlinear Fluctuating Hydrodynamics are obtained with a
proper choice of the slow variables corresponding to the conservation laws. The
resulting model equations are solved in the long time limit to locate the
dynamic transition. The transition point from our model is considerably higher
than predicted in existing MCT models for binary systems. This is in agreement
with what is seen in Computer Simulation of binary fluids. fluids.Comment: 9 Pages, 3 Figure
Solidity of Viscous Liquids
Recent NMR experiments on supercooled toluene and glycerol by Hinze and
Bohmer show that small rotation angles dominate with only few large molecular
rotations. These results are here interpreted by assuming that viscous liquids
are solid-like on short length scales. A characteristic length, the "solidity
length", separates solid-like behavior from liquid-like behavior.Comment: Plain RevTex file, no figure
Growing Correlation Length on Cooling Below the Onset of Caging in a Simulated Glass-Forming Liquid
We present a calculation of a fourth-order, time-dependent density
correlation function that measures higher-order spatiotemporall correlations of
the density of a liquid. From molecular dynamics simulations of a glass-forming
Lennard-Jones liquid, we find that the characteristic length scale of this
function has a maximum as a function of time which increases steadily beyond
the characteristic length of the static pair correlation function in the
temperature range approaching the mode coupling temperature from above
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
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