40 research outputs found
Light quark masses from scalar sum rules
In this work, the mass of the strange quark is calculated from QCD sum rules
for the divergence of the strangeness-changing vector current. The
phenomenological scalar spectral function which enters the sum rule is
determined from our previous work on strangeness-changing scalar form factors
[1]. For the running strange mass in the MS_bar scheme, we find m_s(2 GeV) = 99
+- 16 MeV. Making use of this result and the light-quark mass ratios obtained
from chiral perturbation theory, we are also able to extract the masses of the
lighter quarks m_u and m_d. We then obtain m_u(2 GeV) = 2.9 +- 0.6 MeV and
m_d(2 GeV) = 5.2 +- 0.9 MeV. In addition, we present an updated value for the
light quark condensate.Comment: 19 pages, 2 figures, 1 table, text improved, references added,
version to be published in Eur. Phys. J
On a variant of Giuga numbers
In this paper, we characterize the odd positive integers satisfying the
congruence . We show that
the set of such positive integers has an asymptotic density which turns out to
be slightly larger than 3/8.Comment: 14 page
Meson-Baryon Effective Chiral Lagrangians at O(q^3) Revisited
After our work was published, Frink and Mei{\ss}ner \cite{FM06} pointed out
that our {\cal O}(q^3) three-flavour meson-baryon chiral Lagrangian was not
minimal. Here, we discuss their findings and revise ours accordingly. We find
that eight monomials in our Lagrangian are not independent, but
in addition, two monomials were wrongly discarded, which, as a result, makes
the agreement in the number of independent monomials with \cite{FM06} complete.Comment: 7 pages, 1 table. A mistake was corrected. Our Lagrangian and that of
[2] contain the same number of monomial
The existence of a two-solar mass neutron star constrains the gravitational constant G_N at strong field
In General Relativity there is a maximum mass allowed for neutron stars that,
if exceeded, entails their collapse into a black hole. Its precise value
depends on details of the nuclear matter equation of state about which we are
much more certain thanks to recent progress in low-energy effective theories.
The discovery of a two-solar mass neutron star, near that maximum mass, when
analyzed with modern equations of state, implies that Newton's gravitational
constant in the star cannot exceed its value on Earth by more than 8% at 95%
confidence level. This is a remarkable leap of ten orders of magnitude in the
gravitational field intensity at which the constant has been constrained.Comment: 5 pages including 8 figure