64 research outputs found
A possible experimental determination of from decays
scattering and decays are studied at leading order of
improved chiral perturbation theory. It is shown that high precision experiments at, e.g., DANE should allow for a direct measurement of
the quark mass ratio /.Comment: 9 pages, preprint IPNO-TH 93-17, 2 figures not included, available
upon request, plain Latex, April 199
Light quarks masses and condensates in QCD
We review some theoretical and phenomenological aspects of the scenario in
which the spontaneous breaking of chiral symmetry is not triggered by a
formation of a large condensate . Emphasis is put on the resulting
pattern of light quark masses, on the constraints arising from QCD sum rules
and on forthcoming experimental tests.Comment: 23 pages, 12 Postscript figures, LaTeX, uses svcon2e.sty, to be
published in the Proceedings of the Workshop on Chiral Dynamics 1997, Mainz,
Germany, Sept. 1-5, 199
The Low Energy Amplitude to One and Two Loops
The low-energy amplitude is computed explicitly to two-loop accuracy
in the chiral expansion. It depends only on six independent (combinations of)
low-energy constants which are not fixed by chiral symmetry. Four of these
constants are determined {\it via} sum rules which are evaluated using
scattering data at higher energies. Dependence of the low-energy phase shifts
and of the threshold parameters on the remaining two constants (called
and ) are discussed and compared to the existing data from
experiments. Using generalised PT, the constants and are
related to fundamental QCD parameters such as the quark condensate and the quark mass ratio . It is shown
that forthcoming accurate low-energy data can be used to provide, for
the first time, experimental evidence in favour of or against the existence of
a large quark-antiquark condensate in the QCD vacuum.Comment: 61 pages, LaTeX, 10 figures in separate tarred, compressed and
uuencoded Postscript fil
Order p^6 chiral couplings from the scalar K Pi form factor
Employing results from a recent determination of the scalar KPi form factor
F_0^KPi within a coupled channel dispersion relation analysis \cite{JOP01}, in
this work we calculate the slope and curvature of F_0^KPi(t) at zero momentum
transfer. Knowledge of the slope and curvature of the scalar KPi form factor,
together with a recently calculated expression for F_0^KPi(t) in chiral
perturbation theory at order p^6, enable to estimate the O(p^6) chiral
constants C_12^r=(0.3 +- 5.4)10^-7 and (C_12^r+C_34^r)=(3.2 +- 1.5)10^-6. Our
findings also allow to estimate the contribution coming from the C_i to the
vector form factor F_+^KPi(0) which is crucial for a precise determination of
|V_us| from K_l3 decays. Our result F_+^KPi(0)|_C_i^r=-0.018 +- 0.009, though
inflicted with large uncertainties, is in perfect agreement with a previous
estimate by Leutwyler and Roos already made twenty years ago.Comment: 19 pages, discussion of scale dependence of the chiral couplings
added; version to appear in JHE
Klein tunneling in graphene: optics with massless electrons
This article provides a pedagogical review on Klein tunneling in graphene,
i.e. the peculiar tunneling properties of two-dimensional massless Dirac
electrons. We consider two simple situations in detail: a massless Dirac
electron incident either on a potential step or on a potential barrier and use
elementary quantum wave mechanics to obtain the transmission probability. We
emphasize the connection to related phenomena in optics, such as the
Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot
resonances, negative refraction index materials (the so called meta-materials),
etc. We also stress that Klein tunneling is not a genuine quantum tunneling
effect as it does not necessarily involve passing through a classically
forbidden region via evanescent waves. A crucial role in Klein tunneling is
played by the conservation of (sublattice) pseudo-spin, which is discussed in
detail. A major consequence is the absence of backscattering at normal
incidence, of which we give a new shorten proof. The current experimental
status is also thoroughly reviewed. The appendix contains the discussion of a
one-dimensional toy model that clearly illustrates the difference in Klein
tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added,
several figures slightly modifie
Pi-eta scattering and the resummation of vacuum fluctuation in three-flavour ChPT
We discuss various aspects of resummed chiral perturbation theory, which was
developed recently in order to consistently include the possibility of large
vacuum fluctuations of the ss-pairs and the scenario with smaller value of the
chiral condensate for N_f=3. The subtleties of this approach are illustrated
using a concrete example of observables connected with pi-eta scattering. This
process seems to be a suitable theoretical laboratory for this purpose due to
its sensitivity to the values of the O(p^4) LEC's, namely to the values of the
fluctuation parameters L4 and L6. We discuss several issues in detail, namely
the choice of `good' observables and properties of their bare expansions, the
`safe' reparametrization in terms of physical observables, the implementation
of exact perturbative unitarity and exact renormalization scale independence,
the role of higher order remainders and their estimates. We make a detailed
comparison with standard chiral perturbation theory and use generalized ChPT as
well as resonance chiral theory to estimate the higher order remainders.Comment: Version submitted to EPJ
SJS/TEN 2019: From Science to Translation
Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are potentially life-threatening, immune-mediated adverse reactions characterized by widespread erythema, epidermal necrosis, and detachment of skin and mucosa. Efforts to grow and develop functional international collaborations and a multidisciplinary interactive network focusing on SJS/TEN as an uncommon but high burden disease will be necessary to improve efforts in prevention, early diagnosis and improved acute and long-term management. SJS/TEN 2019: From Science to Translation was a 1.5-day scientific program held April 26-27, 2019, in Vancouver, Canada. The meeting successfully engaged clinicians, researchers, and patients and conducted many productive discussions on research and patient care needs
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