25,377 research outputs found
Canonical Quantization of the Self-Dual Model coupled to Fermions
This paper is dedicated to formulate the interaction picture dynamics of the
self-dual field minimally coupled to fermions. To make this possible, we start
by quantizing the free self-dual model by means of the Dirac bracket
quantization procedure. We obtain, as result, that the free self-dual model is
a relativistically invariant quantum field theory whose excitations are
identical to the physical (gauge invariant) excitations of the free
Maxwell-Chern-Simons theory. The model describing the interaction of the
self-dual field minimally coupled to fermions is also quantized through the
Dirac bracket quantization procedure. One of the self-dual field components is
found not to commute, at equal times, with the fermionic fields. Hence, the
formulation of the interaction picture dynamics is only possible after the
elimination of the just mentioned component. This procedure brings, in turns,
two new interaction terms, which are local in space and time while
non-renormalizable by power counting. Relativistic invariance is tested in
connection with the elastic fermion-fermion scattering amplitude. We prove that
all the non-covariant pieces in the interaction Hamiltonian are equivalent to
the covariant minimal interaction of the self-dual field with the fermions. The
high energy behavior of the self-dual field propagator corroborates that the
coupled theory is non-renormalizable. Certainly, the self-dual field minimally
coupled to fermions bears no resemblance with the renormalizable model defined
by the Maxwell-Chern-Simons field minimally coupled to fermions.Comment: 16 pages, no special macros, no corrections in the pape
Non-Abelian Proca model based on the improved BFT formalism
We present the newly improved Batalin-Fradkin-Tyutin (BFT) Hamiltonian
formalism and the generalization to the Lagrangian formulation, which provide
the much more simple and transparent insight to the usual BFT method, with
application to the non-Abelian Proca model which has been an difficult problem
in the usual BFT method. The infinite terms of the effectively first class
constraints can be made to be the regular power series forms by ingenious
choice of and -matrices. In this new
method, the first class Hamiltonian, which also needs infinite correction terms
is obtained simply by replacing the original variables in the original
Hamiltonian with the BFT physical variables. Remarkably all the infinite
correction terms can be expressed in the compact exponential form. We also show
that in our model the Poisson brackets of the BFT physical variables in the
extended phase space are the same structure as the Dirac brackets of the
original phase space variables. With the help of both our newly developed
Lagrangian formulation and Hamilton's equations of motion, we obtain the
desired classical Lagrangian corresponding to the first class Hamiltonian which
can be reduced to the generalized St\"uckelberg Lagrangian which is non-trivial
conjecture in our infinitely many terms involved in Hamiltonian and Lagrangian.Comment: Notable improvements in Sec. I
Magnetic glass in Shape Memory Alloy : Ni45Co5Mn38Sn12
The first order martensitic transition in the ferromagnetic shape memory
alloy Ni45Co5Mn38Sn12 is also a magnetic transition and has a large field
induced effect. While cooling in the presence of field this first order
magnetic martensite transition is kinetically arrested. Depending on the
cooling field, a fraction of the arrested ferromagnetic austenite phase
persists down to the lowest temperature as a magnetic glassy state, similar to
the one observed in various intermetallic alloys and in half doped manganites.
A detailed investigation of this first order ferromagnetic austenite (FM-A) to
low magnetization martensite (LM-M) state transition as a function of
temperature and field has been carried out by magnetization measurements.
Extensive cooling and heating in unequal field (CHUF) measurements and a novel
field cooled protocol for isothermal MH measurements (FC-MH) are utilized to
investigate the glass like arrested states and show a reverse martensite
transition. Finally, we determine a field -temperature (HT) phase diagram of
Ni45Co5Mn38Sn12 from various magnetization measurements which brings out the
regions where thermodynamic and metastable states co-exist in the HT space
clearly depicting this system as a 'Magnetic Glass'.Comment: Magnetic field tunes kinetic arrest and CHUF shows devitrification
and melting of Magnetic glas
Conversion of glassy antiferromagnetic-insulating phase to equilibrium ferromagnetic-metallic phase by devitrification and recrystallization in Al substituted PrCaMnO
We show that PrCaMnO with 2.5% Al substitution and
LaCaMnO (LCMO) exhibit qualitatively similar and
visibly anomalous M-H curves at low temperature. Magnetic field causes a broad
first-order but irreversible antiferromagnetic (AF)-insulating (I) to
ferromagnetic (FM)-metallic (M) transition in both and gives rise to soft FM
state. However, the low temperature equilibrium state of
PrCaMnAlO (PCMAO) is FM-M whereas that
of LCMO is AF-I. In both the systems the respective equilibrium phase coexists
with the other phase with contrasting order, which is not in equilibrium, and
the cooling field can tune the fractions of the coexisting phases. It is shown
earlier that the coexisting FM-M phase behaves like `magnetic glass' in LCMO.
Here we show from specially designed measurement protocols that the AF-I phase
of PCMAO has all the characteristics of magnetic glassy states. It devitrifies
on heating and also recrystallizes to equilibrium FM-M phase after annealing.
This glass-like AF-I phase also shows similar intriguing feature observed in
FM-M magnetic glassy state of LCMO that when the starting coexisting fraction
of glass is larger, successive annealing results in larger fraction of
equilibrium phase. This similarity between two manganite systems with
contrasting magnetic orders of respective glassy and equilibrium phases points
toward a possible universality.Comment: Highlights potential of CHUF (Cooling and Heating in Unequal Fields),
a new measurement protoco
Magnetocaloric properties of nanocrystalline LaCaMnO
Some recent experimental studies show the invisibility of antiferromagnetic
transition in the cases of manganites when their particle size is reduced to
nanometer scale. In complete contrast to these cases, we have observed the
signature of antiferromagnetic transition in the magnetocaloric properties of
nanocrystalline LaCaMnO of average particle size 70
and 60 nm similar to its polycrystalline bulk form. The system exhibit inverse
magnetocaloric effect in its polycrystalline and nanocrystalline form. An extra
ferromagnetic phase is stabilized at low temperature for the sample with
particle size nm.Comment: 3 Figure
Development of an integrated BEM approach for hot fluid structure interaction: BEST-FSI: Boundary Element Solution Technique for Fluid Structure Interaction
As part of the continuing effort at NASA LeRC to improve both the durability and reliability of hot section Earth-to-orbit engine components, significant enhancements must be made in existing finite element and finite difference methods, and advanced techniques, such as the boundary element method (BEM), must be explored. The BEM was chosen as the basic analysis tool because the critical variables (temperature, flux, displacement, and traction) can be very precisely determined with a boundary-based discretization scheme. Additionally, model preparation is considerably simplified compared to the more familiar domain-based methods. Furthermore, the hyperbolic character of high speed flow is captured through the use of an analytical fundamental solution, eliminating the dependence of the solution on the discretization pattern. The price that must be paid in order to realize these advantages is that any BEM formulation requires a considerable amount of analytical work, which is typically absent in the other numerical methods. All of the research accomplishments of a multi-year program aimed toward the development of a boundary element formulation for the study of hot fluid-structure interaction in Earth-to-orbit engine hot section components are detailed. Most of the effort was directed toward the examination of fluid flow, since BEM's for fluids are at a much less developed state. However, significant strides were made, not only in the analysis of thermoviscous fluids, but also in the solution of the fluid-structure interaction problem
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