854 research outputs found
M-theory and U-duality on with gauge backgrounds
The full U-duality symmetry of toroidally compactified M-theory can be displayed by allowing non-rectangular tori with expectation values of the gauge fields. We derive the couplings in the Matrix gauge theory due to expectation values of the M-theory three-form C. An E_d(Z) U-duality invariant mass formula incorporating nonvanishing gauge backgrounds is also obtained, and is found to agree with these couplings. We show that the conjectured extended U-duality symmetry of Matrix theory on T^d in the Discrete Light-Cone Quantization has an implementation as an action of E_{d+1}(Z) on the BPS spectrum. Some implications for the proper interpretation of the rank N of the Matrix gauge theory are discussed
On rolling, tunneling and decaying in some large N vector models
Various aspects of time-dependent processes are studied within the large N
approximation of O(N) vector models in three dimensions. These include the
rolling of fields, the tunneling and decay of vacua. We present an exact
solution for the quantum conformal case and find a solution for more general
potentials when the total change of the value of the field is small.
Characteristic times are found to be shorter when the time dependence of the
field is taken into account in constructing the exact large N effective
potentials. We show that the different approximations yield the same answers in
the regions of the overlap of the validity. A numerical solution of this
potential reveals a tunneling in which the bubble that separates the true
vacuum from the false one is thick
Soliton solutions in an effective action for SU(2) Yang-Mills theory: including effects of higher-derivative term
The Skyrme-Faddeev-Niemi (SFN) model which is an O(3) model in three
dimensional space upto fourth-order in the first derivative is regarded as a
low-energy effective theory of SU(2) Yang-Mills theory. One can show from the
Wilsonian renormalization group argument that the effective action of
Yang-Mills theory recovers the SFN in the infrared region. However, the thoery
contains an additional fourth-order term which destabilizes the soliton
solution. In this paper, we derive the second derivative term perturbatively
and show that the SFN model with the second derivative term possesses soliton
solutions.Comment: 7 pages, 3 figure
Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor
After the very long consideration of the ideal energy source by fusion of the
protons of light hydrogen with the boron isotope 11 (boron fusion HB11) the
very first two independent measurements of very high reaction gains by lasers
basically opens a fundamental breakthrough. The non-thermal plasma block
ignition with extremely high power laser pulses above petawatt of picosecond
duration in combination with up to ten kilotesla magnetic fields for trapping
has to be combined to use the measured high gains as proof of an avalanche
reaction for an environmentally clean, low cost and lasting energy source as
potential option against global warming. The unique HB11 avalanche reaction is
are now based on elastic collisions of helium nuclei (alpha particles) limited
only to a reactor for controlled fusion energy during a very short time within
a very small volume.Comment: 11 pages, 6 figures, Submitted to Proceedings 2nd Symposium High
Power Laser Science and Engineering, 14-18 MARCH 2016, Suzhou/Chin
Observation of quantum depletion in a nonequilibrium exciton-polariton condensate
The property of superfluidity, first discovered in liquid 4He, is closely
related to Bose-Einstein condensation (BEC) of interacting bosons. However,
even at zero temperature, when one would expect the whole bosonic quantum
liquid to become condensed, a fraction of it is excited into higher momentum
states via interparticle interactions and quantum fluctuations -- the
phenomenon of quantum depletion. Quantum depletion of weakly interacting atomic
BECs in thermal equilibrium is well understood theoretically but is difficult
to measure. This is even more challenging in driven-dissipative systems such as
exciton-polariton condensates(photons coupled to electron-hole pairs in a
semiconductor), since their nonequilibrium nature is predicted to suppress
quantum depletion. Here, we observe quantum depletion of an optically trapped
high-density exciton-polariton condensate by directly detecting the spectral
branch of elementary excitations populated by this process. Analysis of the
population of this branch in momentum space shows that quantum depletion of an
exciton-polariton condensate can closely follow or strongly deviate from the
equilibrium Bogoliubov theory, depending on the fraction of matter (exciton) in
an exciton-polariton. Our results reveal the effects of exciton-polariton
interactions beyond the mean-field description and call for a deeper
understanding of the relationship between equilibrium and nonequilibrium BECs.Comment: 18 pages, 5 figures, with supplementary informatio
Multitrace Deformations of Vector and Adjoint Theories and their Holographic Duals
We present general methods to study the effect of multitrace deformations in
conformal theories admitting holographic duals in Anti de Sitter space. In
particular, we analyse the case that these deformations introduce an
instability both in the bulk AdS space and in the boundary CFT. We also argue
that multitrace deformations of the O(N) linear sigma model in three dimensions
correspond to nontrivial time-dependent backgrounds in certain theories of
infinitely many interacting massless fields on AdS_4, proposed years ago by
Fradkin and Vasiliev. We point out that the phase diagram of a truly marginal
large-N deformation has an infrared limit in which only an O(N) singlet field
survives. We draw from this case lessons on the full string-theoretical
interpretation of instabilities of the dual boundary theory and exhibit a toy
model that resolves the instability of the O(N) model, generated by a marginal
multitrace deformation. The resolution suggests that the instability may not
survive in an appropriate UV completion of the CFT.Comment: 18 pages, minor changes, references added. Version accepted by JHE
Corrosion Control in Industry
The economic development of any region, state or country, depends not only on its natural reâ sources and productive activities, but also on the infrastructure that account for the exploitaâ tion, processing and marketing of goods. Irrigation systems, roads, bridges, airports, maritime, land and air transport, school buildings, offices and housing, industrial installations are affectâ ed by corrosion and therefore susceptible to deterioration and degradation processes
Hamiltonian Formalism for Space-time Non-commutative Theories
Space-time non-commutative theories are non-local in time. We develop the
Hamiltonian formalism for non-local field theories in d space-time dimensions
by considering auxiliary d+1 dimensional field theories which are local with
respect to the evolution time. The Hamiltonian path integral quantization is
considered and the Feynman rules in the Lagrangian formalism are derived. The
case of non-commutative \phi^3 theory is considered as an example.Comment: 6 pages, A new section is added with other comments and references.
To appear in PR
Automatic Segmentation of Muscle Tissue and Inter-muscular Fat in Thigh and Calf MRI Images
Magnetic resonance imaging (MRI) of thigh and calf muscles is one of the most
effective techniques for estimating fat infiltration into muscular dystrophies.
The infiltration of adipose tissue into the diseased muscle region varies in
its severity across, and within, patients. In order to efficiently quantify the
infiltration of fat, accurate segmentation of muscle and fat is needed. An
estimation of the amount of infiltrated fat is typically done visually by
experts. Several algorithmic solutions have been proposed for automatic
segmentation. While these methods may work well in mild cases, they struggle in
moderate and severe cases due to the high variability in the intensity of
infiltration, and the tissue's heterogeneous nature. To address these
challenges, we propose a deep-learning approach, producing robust results with
high Dice Similarity Coefficient (DSC) of 0.964, 0.917 and 0.933 for
muscle-region, healthy muscle and inter-muscular adipose tissue (IMAT)
segmentation, respectively.Comment: 9 pages, 4 figures, 2 tables, MICCAI 2019, the 22nd International
Conference on Medical Image Computing and Computer Assisted Interventio
- …