1,546 research outputs found
Renormalized Wick expansion for a modified PQCD
The renormalization scheme for the Wick expansion of a modified version of
the perturbative QCD introduced in previous works is discussed. Massless QCD is
considered, by implementing the usual multiplicative scaling of the gluon and
quark wave functions and vertices. However, also massive quark and gluon
counter-terms are allowed in this mass less theory since the condensates are
expected to generate masses. A natural set of expansion parameters of the
physical quantities is introduced: the coupling itself and to masses and
associated to quarks and gluons respectively. This procedure allows to
implement a dimensional transmutation effect through these new mass scales. A
general expression for the new generating functional in terms of the mass
parameters and is obtained in terms of integrals over arbitrary but
constant gluon or quark fields in each case. Further, the one loop potential,
is evaluated in more detail in the case when only the quark condensate is
retained. This lowest order result again indicates the dynamical generation of
quark condensates in the vacuum.Comment: 13 pages, one figur
Faddeev-Jackiw approach to gauge theories and ineffective constraints
The general conditions for the applicability of the Faddeev-Jackiw approach
to gauge theories are studied. When the constraints are effective a new proof
in the Lagrangian framework of the equivalence between this method and the
Dirac approach is given. We find, however, that the two methods may give
different descriptions for the reduced phase space when ineffective constraints
are present. In some cases the Faddeev-Jackiw approach may lose some
constraints or some equations of motion. We believe that this inequivalence can
be related to the failure of the Dirac conjecture (that says that the Dirac
Hamiltonian can be enlarged to an Extended Hamiltonian including all first
class constraints, without changes in the dynamics) and we suggest that when
the Dirac conjecture fails the Faddeev-Jackiw approach fails to give the
correct dynamics. Finally we present some examples that illustrate this
inequivalence.Comment: 21 pages, Latex. To be published in Int. J. Mod. Phys.
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An observational study of pediatric healthcare burden in Angelman syndrome: results from a real-world study.
BACKGROUND:The objective of this study is to describe variations in the healthcare resource utilization (HRU) among individuals with Angelman syndrome (AS) over the first 12âyears of life. Data for this study were drawn from the AS Natural History study (ASNHS), which is an observational study on the developmental progress, behavior, and medical morbidity of individuals with AS conducted over eight years. Caregiver-reported information on hospitalization, surgery, and medication utilization was used to assess HRU. Repeated measures mixed effect models were used to assess the relationship between age and probability of hospitalization, surgery, and prescription medication utilization. RESULTS:Mean age at study enrollment was 6âyears of age and both sexes were equally represented. The mean number of visits per participant was three. Results from this study suggest that individuals with AS have a high HRU burden. Hospitalization and surgery burden were highest in the first year of life. Use of medications for seizures and sleep disturbance increased over time. CONCLUSIONS:The study highlights the significant healthcare burden among individuals with AS. Future studies that estimate cost and caregiver burden associated with AS are needed to assess the lifelong economic impact of AS on families and healthcare system
Classical Noncommutative Electrodynamics with External Source
In a -noncommutative (NC) gauge field theory we extend the
Seiberg-Witten (SW) map to include the (gauge-invariance-violating) external
current and formulate - to the first order in the NC parameter -
gauge-covariant classical field equations. We find solutions to these equations
in the vacuum and in an external magnetic field, when the 4-current is a static
electric charge of a finite size , restricted from below by the elementary
length. We impose extra boundary conditions, which we use to rule out all
singularities, included, from the solutions. The static charge proves to
be a magnetic dipole, with its magnetic moment being inversely proportional to
its size . The external magnetic field modifies the long-range Coulomb field
and some electromagnetic form-factors. We also analyze the ambiguity in the SW
map and show that at least to the order studied here it is equivalent to the
ambiguity of adding a homogeneous solution to the current-conservation
equation
On the non-relativistic limit of charge conjugation in QED
Even if at the level of the non-relativistic limit of full QED, C is not a
symmetry, the limit of this operation does exist for the particular case when
the electromagnetic field is considered a classical external object coupled to
the Dirac field. This result extends the one obtained when fermions are
described by the Schroedinger-Pauli equation. We give the expressions for both
the C matrix and the operator for galilean electrons and positrons
interacting with the external electromagnetic field. The result is relevant in
relation to recent experiments with antihydrogen.Comment: 7 page
1/N expansion of the D3-D5 defect CFT at strong coupling
We consider four dimensional U(N) N = 4 SYM theory interacting with a 3d N = 4 theory living on a co dimension-one interface and holographically dual to the D3-D5 system without flux. Localization captures several observables in this dCFT, including its free energy, related to the defect expectation value, and single trace 1/2-BPS composite scalars. These quantities may be computed in a hermitian one-matrix model with non polynomial single-trace potential. We exploit the integrable Volterra hierarchy underlying the matrix model and systematically study its 1/N expansion at any value of the 't Hooft coupling. In particular, the strong coupling regime is determined - up to non-perturbative exponentially suppressed corrections - by differential relations that constrain higher order terms in the 1/N expansion. The analysis is extended to the model with SU(N) gauge symmetry by resorting to the more general Toda lattice equations
Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal
The in-plane diamagnetism around the Meissner transition was measured in a
TlBaCaCuO single crystal of high chemical and structural
quality, which minimizes the inhomogeneity and disorder rounding effects on the
magnetization. When analyzed quantitatively and consistently above and below
the transition in terms of the Ginzburg-Landau (GL) approach with fluctuations
of Cooper pairs and vortices, these data provide a further confirmation that
the observed Meissner transition is a conventional GL superconducting
transition in a homogeneous layered superconductor.Comment: 5 pages, including 3 figure
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