1,998 research outputs found

### Baryon electric dipole moments from strong CP violation

The electric dipole form factors and moments of the ground state baryons are
calculated in chiral perturbation theory at next-to-leading order. We show that
the baryon electric dipole form factors at this order depend only on two
combinations of low-energy constants. We also derive various relations that are
free of unknown low-energy constants. We use recent lattice QCD data to
calculate all baryon EDMs. In particular, we find d_n = -2.9\pm 0.9 and d_p =
1.1\pm 1.1 in units of 10^{-16} e \theta_0 cm. Finite volume corrections to the
moments are also worked out. We show that for a precision extraction from
lattice QCD data, the next-to-leading order terms have to be accounted for.Comment: 30 pages, 8 figures, to appear in JHE

### Triangular singularity and a possible $\phi p$ resonance in the $\Lambda^+_c \to \pi^0 \phi p$ decay

We study the $\Lambda^+_c \to \pi^0 \phi p$ decay by considering a triangle
singularity mechanism. In this mechanism, the $\Lambda^+_c$ decays into the
$K^* \Sigma^*(1385)$, the $\Sigma^*(1385)$ decays into the $\pi^0 \Sigma$ (or
$\Lambda$), and then the $K^* \Sigma$ (or $\Lambda$) interact to produce the
$\phi p$ in the final state. This mechanism produces a peak structure around
$2020$ MeV. In addition, the possibility that there is a hidden-strange
pentaquark-like state is also considered by taking into account the final state
interactions of $K^* \Lambda$, $K^* \Sigma$, and $\phi p$. We conclude that it
is difficult to search for the hidden-strange analogue of the $P_c$ states in
this decay. However, we do expect nontrivial behavior in the $\phi p$ invariant
mass distribution. The predictions can be tested by experiments such as BESIII,
LHCb and Belle-II.Comment: 7 pages, 3 figure

### Light quark mass dependence in heavy quarkonium physics

The issue of chiral extrapolations in heavy quarkonium systems is discussed.
We show that the light quark mass dependence of the properties of heavy
quarkonia is not always suppressed. For quarkonia close to an open flavor
threshold, even a nonanalytic chiral extrapolation is needed. Both these
nontrivial facts are demonstrated to appear in the decay widths of the hindered
M1 transitions between the first radially excited and ground state P-wave
charmonia. The results at a pion mass of about 500 MeV could deviate from the
value at the physical pion mass by a factor of two. Our findings show the
necessity of performing chiral extrapolations for lattice simulations of heavy
quarkonium systems.Comment: 5 pages, 5 figures. Version to appear in Phys. Rev. Let

### Isospin and a possible interpretation of the newly observed X(1576)

Recently, the BES collaboration observed a broad resonant structure X(1576)
with a large width being around 800 MeV and assigned its $J^{PC}$ number to
$1^{--}$. We show that the isospin of this resonant structure should be
assigned to 1. This state might be a molecule state or a tetraquark state. We
study the consequences of a possible $K^*(892)$-${\bar \kappa}$ molecular
interpretation. In this scenario, the broad width can easily be understood. By
using the data of $B(J/\psi\to X\pi^0)\cdot B(X\to K^+K^-)$, the branching
ratios $B(J/\psi\to X\pi^0)\cdot B(X\to \pi^+\pi^-)$ and $B(J/\psi\to
X\pi^0)\cdot B(X\to K^+K^-\pi^+\pi^-)$ are further estimated in this molecular
state scenario. It is shown that the $X\to \pi^+\pi^-$ decay mode should have a
much larger branching ratio than the $X\to K^+K^-$ decay mode has. As a
consequence, this resonant structure should also be seen in the $J/\psi\to
\pi^+\pi^-\pi^0$ and $J/\psi\to K^+K^-\pi^+\pi^-\pi^0$ processes, especially in
the former process. Carefully searching this resonant structure in the
$J/\psi\to \pi^+\pi^-\pi^0$ and $J/\psi\to K^+K^-\pi^+\pi^-\pi^0$ decays should
be important for understanding the structure of X(1567).Comment: 5 pages, ReVTeX4, 3 figures. Version accepted for publication as a
brief report in Phys. Rev.

### Cumulants of the QCD topological charge distribution

The distribution of the QCD topological charge can be described by cumulants,
with the lowest one being the topological susceptibility. The vacuum energy
density in a theta-vacuum is the generating function for these cumulants. In
this paper, we derive the vacuum energy density in SU(2) chiral perturbation
theory up to next-to-leading order keeping different up and down quark masses,
which can be used to calculate any cumulant of the topological charge
distribution. We also give the expression for the case of SU(N) with degenerate
quark masses. In this case, all cumulants depend on the same linear combination
of low-energy constants and chiral logarithm, and thus there are sum rules
between the N-flavor quark condensate and the cumulants free of next-to-leading
order corrections.Comment: match the version published in PL

### Effective Field Theory in The Study of Long Range Nuclear Parity Violation on Lattice

A non-zero signal $A_\gamma^\mathrm{np}=(-3.0\pm1.4\pm0.2)\times 10^{-8}$ of
the gamma-ray asymmetry in the neutron-proton capture was recently reported by
the NPDGamma Collaboration which provides the first determination of the
$\Delta I=1$ parity-odd pion-nucleon coupling constant $h_\pi^1=(2.6\pm 1.2\pm
0.2)\times 10^{-7}$. The ability to reproduce this value from first principles
serves as a direct test of our current understanding of the interplay between
the strong and weak interaction at low energy. To motivate new lattice studies
of $h_\pi^1$, we review the current status of the theoretical understanding of
this coupling, which includes our recent work that relates it to a nucleon
mass-splitting by a soft-pion theorem. We further investigate the possibility
of calculating the mass-splitting on the lattice by providing effective field
theory parameterizations of all the involved quark contraction diagrams. We
show that the lattice calculations of the easier connected diagrams will
provide information of the chiral logarithms in the much harder quark loop
diagrams and thus help in the chiral extrapolation of the latter.Comment: 43 pages, 3 figures, 1 table. Accepted by EPJ

### Anomalous decays of eta' and eta into four pions

We calculate the branching ratios of the yet unmeasured eta' decays into four
pions, based on a combination of chiral perturbation theory and vector-meson
dominance. The decays eta' --> 2(pi+ pi-) and eta' --> pi+ pi- 2pi0 are P-wave
dominated and can largely be thought to proceed via two rho resonances; we
predict branching fractions of (1.0+-0.3)*10^-4 and (2.4+-0.7)*10^-4,
respectively, not much lower than the current experimental upper limits. The
decays eta' --> 4pi0 and eta --> 4pi0, in contrast, are D-wave driven as long
as conservation of CP symmetry is assumed, and are significantly further
suppressed; any experimental evidence for the decay eta --> 4pi0 could almost
certainly be interpreted as a signal of CP violation. We also calculate the
CP-violating amplitudes for eta' --> 4pi0 and eta --> 4pi0 induced by the QCD
theta-term.Comment: 13 pages, 5 figures; references updated, version published in Phys.
Rev.

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