1,213 research outputs found
Pathogenesis, risk factors and therapeutic options for autoimmune haemolytic anaemia in the post-transplant setting
Autoimmune haemolytic anaemia (AIHA) is a rare complication of allogeneic haematopoietic stem cell transplantation (HSCT), observed with an incidence of 1–5%. Paediatric age, diagnosis of non-malignant disease, lympho-depleting agents in the conditioning regimen, use of unrelated donor, graft versus host disease and infections have been associated with a higher risk of AIHA post HSCT. Post-HSCT AIHA is associated with high mortality and morbidity, and it is often very difficult to treat. Steroids and rituximab are used with a response rate around 30–50%. These and other therapeutic strategies are mainly derived from data on primary AIHA, although response rates in post-HSCT AIHA have been generally lower. Here we review the currently available data on risk factors and therapeutic options. There is a need for prospective studies in post-HSCT AIHA to guide clinicians in managing these complex patients
Zero mode in the time-dependent symmetry breaking of theory
We apply the quartic exponential variational approximation to the symmetry
breaking phenomena of scalar field in three and four dimensions. We calculate
effective potential and effective action for the time-dependent system by
separating the zero mode from other non-zero modes of the scalar field and
treating the zero mode quantum mechanically. It is shown that the quantum
mechanical properties of the zero mode play a non-trivial role in the symmetry
breaking of the scalar theory.Comment: 10 pages, 3 figure
An O(N) symmetric extension of the Sine-Gordon Equation
We discuss an O(N) exension of the Sine-Gordon (S-G)equation which allows us
to perform an expansion around the leading order in large-N result using
Path-Integral methods. In leading order we show our methods agree with the
results of a variational calculation at large-N. We discuss the striking
differences for a non-polynomial interaction between the form for the effective
potential in the Gaussian approximation that one obtains at large-N when
compared to the N=1 case. This is in contrast to the case when the classical
potential is a polynomial in the field and no such drastic differences occur.
We find for our large-N extension of the Sine-Gordon model that the unbroken
ground state is unstable as one increases the coupling constant (as it is for
the original S-G equation) and we determine the stability criteria.Comment: 21 pages, Latex (Revtex4) v3:minor grammatical changes and addition
Mean field theory for collective motion of quantum meson fields
Mean field theory for the time evolution of quantum meson fields is studied
in terms of the functional Schroedinger picture with a time-dependent Gaussian
variational wave functional. We first show that the equations of motion for the
variational wavefunctional can be rewritten in a compact form similar to the
Hartree-Bogoliubov equations in quantum many-body theory and this result is
used to recover the covariance of the theory. We then apply this method to the
O(N) model and present analytic solutions of the mean field evolution equations
for an N-component scalar field. These solutions correspond to quantum
rotations in isospin space and represent generalizations of the classical
solutions obtained earlier by Anselm and Ryskin. As compared to classical
solutions new effects arise because of the coupling between the average value
of the field and its quantum fluctuations. We show how to generalize these
solutions to the case of mean field dynamics at finite temperature. The
relevance of these solutions for the observation of a coherent collective state
or a disoriented chiral condensate in ultra-relativistic nuclear collisions is
discussed.Comment: 31 pages, 2 Postscript figures, uses ptptex.st
Quantum Decoherence, Entropy and Thermalization in Strong Interactions at High Energy
Entropy is generated in high-multiplying events by a dynamical separation of
strongly interacting systems into partons and unobservable environment modes
(almost constant field configurations) due to confinement.Comment: 45 pages, 2 figure
Semiclassical Symmetries
Essential properties of semiclassical approximation for quantum mechanics are
viewed as axioms of an abstract semiclassical mechanics. Its symmetry
properties are discussed. Semiclassical systems being invariant under Lie
groups are considered. An infinitesimal analog of group relation is written.
Sufficient conditions for reconstructing semiclassical group transformations
(integrability of representation of Lie algebra) are discussed. The obtained
results may be used for mathematical proof of Poincare invariance of
semiclasical Hamiltonian field theory and for investigation of quantum
anomalies.Comment: LaTeX, 33 page
Effective action and the quantum equation of motion
We carefully analyse the use of the effective action in dynamical problems,
in particular the conditions under which the equation \frac{\delta \Ga}
{\delta \phi}=0 can be used as a quantum equation of motion, and the relation
between the asymptotic states involved in the definition of \Ga and the
initial state of the system. By considering the quantum mechanical example of a
double-well potential, where we can get exact results for the time evolution of
the system, we show that an approximation to the effective potential in the
quantum equation of motion that correctly describes the dynamical evolution of
the system is obtained with the help of the wilsonian RG equation (already at
the lowest order of the derivative expansion), while the commonly used one-loop
effective potential fails to reproduce the exact results.Comment: 28 pages, 13 figures. Revised version to appear in The European
Physical Journal
Resumming the large-N approximation for time evolving quantum systems
In this paper we discuss two methods of resumming the leading and next to
leading order in 1/N diagrams for the quartic O(N) model. These two approaches
have the property that they preserve both boundedness and positivity for
expectation values of operators in our numerical simulations. These
approximations can be understood either in terms of a truncation to the
infinitely coupled Schwinger-Dyson hierarchy of equations, or by choosing a
particular two-particle irreducible vacuum energy graph in the effective action
of the Cornwall-Jackiw-Tomboulis formalism. We confine our discussion to the
case of quantum mechanics where the Lagrangian is . The
key to these approximations is to treat both the propagator and the
propagator on similar footing which leads to a theory whose graphs have the
same topology as QED with the propagator playing the role of the photon.
The bare vertex approximation is obtained by replacing the exact vertex
function by the bare one in the exact Schwinger-Dyson equations for the one and
two point functions. The second approximation, which we call the dynamic Debye
screening approximation, makes the further approximation of replacing the exact
propagator by its value at leading order in the 1/N expansion. These two
approximations are compared with exact numerical simulations for the quantum
roll problem. The bare vertex approximation captures the physics at large and
modest better than the dynamic Debye screening approximation.Comment: 30 pages, 12 figures. The color version of a few figures are
separately liste
Schwinger-Dyson approach to non-equilibrium classical field theory
In this paper we discuss a Schwinger-Dyson [SD] approach for determining the
time evolution of the unequal time correlation functions of a non-equilibrium
classical field theory, where the classical system is described by an initial
density matrix at time . We focus on field theory in 1+1
space time dimensions where we can perform exact numerical simulations by
sampling an ensemble of initial conditions specified by the initial density
matrix. We discuss two approaches. The first, the bare vertex approximation
[BVA], is based on ignoring vertex corrections to the SD equations in the
auxiliary field formalism relevant for 1/N expansions. The second approximation
is a related approximation made to the SD equations of the original formulation
in terms of alone. We compare these SD approximations as well as a
Hartree approximation with exact numerical simulations. We find that both
approximations based on the SD equations yield good agreement with exact
numerical simulations and cure the late time oscillation problem of the Hartree
approximation. We also discuss the relationship between the quantum and
classical SD equations.Comment: 36 pages, 5 figure
Out-of-equilibrium evolution of quantum fields in the hybrid model with quantum back reaction
The hybrid model with a scalar "inflaton" field coupled to a "Higgs" field
with a broken symmetry potential is one of the promising models for inflation
and (p)reheating after inflation. We consider the nonequilibrium evolution of
the quantum fields of this model with quantum back reaction in the Hartree
approximation, in particular the transition of the Higgs field from the
metastable "false vacuum" to the broken symmetry phase. We have performed the
renormalization of the equations of motion, of the gap equations and of the
energy density, using dimensional regularization. We study the influence of the
back reaction on the evolution of the classical fields and of the quantum
fluctuations. We observe that back reaction plays an important role over a wide
range of parameters. Some implications of our investigation for the preheating
stage after cosmic inflation are presented.Comment: 35 pages, 16 eps figures, revtex4; v2: typos corrected and references
added, accepted for publication in Physical Review
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