25,176 research outputs found
Note on the space group selection rule for closed strings on orbifolds
It is well-known that the space group selection rule constrains the
interactions of closed strings on orbifolds. For some examples, this rule has
been described by an effective Abelian symmetry that combines with a
permutation symmetry to a non-Abelian flavor symmetry like or
. However, the general case of the effective Abelian symmetries was
not yet fully understood. In this work, we formalize the computation of the
Abelian symmetry that results from the space group selection rule by imposing
two conditions only: (i) well-defined discrete charges and (ii) their
conservation. The resulting symmetry, which we call the space group flavor
symmetry , is uniquely specified by the Abelianization of the space group.
For all Abelian orbifolds with supersymmetry we compute and
identify new cases, for example, where contains a dark
matter-parity with charges 0 and 1 for massless and massive strings,
respectively.Comment: 28 pages, 1 tabl
Evidence for the two pole structure of the Lambda(1405) resonance
The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary
model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows,
in agreement with a recent experiment, a peak at 1420 MeV and a relatively
narrow width of Gamma = 38 MeV. The mechanism for the reaction is largely
dominated by the emission of a pi^0 prior to the K^- p interaction leading to
the Lambda(1405). This ensures the coupling of the Lambda(1405) to the K^- p
channel, thus maximizing the contribution of the second state found in chiral
unitary theories, which is narrow and of higher energy than the nominal
Lambda(1405). This is unlike the pi^- p --> K^0 \pi Sigma reaction, which gives
more weight to the pole at lower energy and with a larger width. The data of
these two experiments, together with the present theoretical analysis, provides
a firm evidence of the two pole structure of the Lambda(1405).Comment: 4 pages, 6 figure
Mirage Torsion
Z_NxZ_M orbifold models admit the introduction of a discrete torsion phase.
We find that models with discrete torsion have an alternative description in
terms of torsionless models. More specifically, discrete torsion can be 'gauged
away' by changing the shifts by lattice vectors. Similarly, a large class of
the so-called generalized discrete torsion phases can be traded for changing
the background fields (Wilson lines) by lattice vectors. We further observe
that certain models with generalized discrete torsion are equivalent to
torsionless models with the same gauge embedding but based on different
compactification lattices. We also present a method of classifying heterotic
Z_NxZ_M orbifolds.Comment: 26 pages, 3 figures, v2: matches version published in JHE
Experimental status of deeply bound kaonic states in nuclei
We review recent claims of the existence of deeply bound kaonic states in
nuclei. Also we study in details the (K-,p) reaction on C12 with 1 GeV/c
momentum kaon beam, based on which a deep kaon nucleus optical potential was
claimed in [1]. In our Monte Carlo simulation of this reaction we include not
only the quasi-elastic K- p scattering, as in [1], but also K- absorption by
one and two nucleons followed by the decay of the hyperon in pi N, which can
also produce strength in the region of interest. The final state interactions
in terms of multiple scattering of the K-, p and all other primary particles on
their way out of the nucleus is also considered. We will show that all these
additional mechanisms allow us to explain the observed spectrum with a
"standard" shallow kaon nucleus optical potential obtained in chiral models.
[1] T. Kishimoto et al., Prog. Theor. Phys. 118, 181 (2007).Comment: 5 pages, 3 figures. To be published in the Proceedings of the
International Workshop on Chiral Symmetry in Hadrons and Nuclei (Chiral10),
Valencia, Spain, June 21-24, 201
A note on discrete R symmetries in Z6-II orbifolds with Wilson lines
We re-derive the R symmetries for the Z6-II orbifold with non-trivial Wilson
lines and find expressions for the R charges which differ from those in the
literature.Comment: 13 pages, 3 figure
The ratio FK/Fpi in QCD
We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based
on a series of lattice calculations with three different lattice spacings,
large volumes and a simulated pion mass reaching down to about 190 MeV. We
obtain FK/Fpi=1.192 +/- 0.007(stat) +/- 0.006(syst). This result is then used
to give an updated value of the CKM matrix element |Vus|. The unitarity
relation for the first row of this matrix is found to be well observed.Comment: 15 pages, 4 figures, 2 table
A theoretical description of energy spectra and two-neutron separation energies for neutron-rich zirconium isotopes
Very recently the atomic masses of neutron-rich Zr isotopes, from Zr
to Zr, have been measured with high precision. Using a schematic
Interacting Boson Model (IBM) Hamiltonian, the evolution from spherical to
deformed shapes along the chain of Zr isotopes, describing at the same time the
excitation energies as well as the two-neutron separation energies, can be
rather well reproduced. The interplay between phase transitions and
configuration mixing of intruder excitations in this mass region is succinctly
addressed.Comment: Accepted in European Journal of Physics
Electromagnetic corrections to light hadron masses
At the precision reached in current lattice QCD calculations, electromagnetic
effects are becoming numerically relevant. We will present preliminary results
for electromagnetic corrections to light hadron masses, based on simulations in
which a degree of freedom is superimposed on QCD
configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice
Field Theory, June 14-19,2010, Villasimius, Sardinia Ital
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