125 research outputs found

### Indications of the possible observation of the lowest-lying 1^{-+} QCD state

We discuss properties of 1^{-+} exotic mesons within the framework of the QCD
field-theoretic approach. We estimate the mass of the lowest-lying 1^{-+}
exotic meson using renormalization-improved QCD sum rules, and find that the
mass lies around $1.26\pm 0.15$ GeV, in good agreement with the $\pi_1(1400)$
data. This state should be expected in QCD. We find that the mass for the
lowest-lying strange 1^{-+} meson is $1.31\pm 0.19$ GeV. Our result hints that
the K^*(1410) may be the lowest-lying 1^{-+} nonet state.Comment: 6 pages, 3 figures; some typos corrected, Published versio

### Thermodynamic Evolution of Secluded Vector Dark Matter: Conventional WIMPs and Nonconventional WIMPs

The secluded dark matter resides within a hidden sector and self-annihilates
into lighter mediators which subsequently decay to the Standard Model (SM)
particles. Depending on the coupling strength of the mediator to the SM, the
hidden sector can be kinetically decoupled from the SM bath when the
temperature drops below the mediator's mass, and the dark matter annihilation
cross section at freeze-out is thus possible to be boosted above the
conventional value of weak interacting massive particles. We present a
comprehensive study on thermodynamic evolution of the hidden sector from the
first principle, using the simplest secluded vector dark matter model.
Motivated by the observation of Galactic center gamma-ray excess, we take two
mass sets $\sim{\cal O}(80\, \text{GeV})$ for the dark matter and mediator as
examples to illustrate the thermodynamics. The coupled Boltzmann moment
equations for number densities and temperature evolutions of the hidden sector
are numerically solved. The formalism can be easily extended to a general
secluded dark matter model. We show that a long-lived mediator can result in a
boosted dark matter annihilation cross section to account for the relic
abundance. We further show the parameter space which provides a good fit to the
Galactic center excess data and is compatible with the current bounds and
LUX-ZEPLIN projected sensitivity. We find that the future observations of dwarf
spheroidal galaxies offer promising reach to probe the most relic allowed
parameter space relevant to the boosted dark matter annihilation cross section.Comment: 51 pages, 15 figures; typos corrected in (42), (45) and (46); in the
text and caption of Fig. 6, variations of the local density and inner slope
of the halo corrected to be consistent with the plot

### Branching Ratios and CP Asymmetries of B \to a_1(1260) \pi and a_1(1260) K Decays

We present the studies of the decays $B\to a_1(1260) \pi$ and $a_1(1260) K$
within the framework of QCD factorization. Due to the G-parity, unlike the
vector meson, the chiral-odd two-parton light-cone distribution amplitudes of
the $a_1$ are antisymmetric under the exchange of quark and anti-quark momentum
fractions in the SU(2) limit. The branching ratios for $a_1 \pi$ modes are
sensitive to tree--penguin interference. The resultant ${\cal B}(B^0 \to
a_1^\pm \pi^\mp)$ are in good agreement with the data. However, using the
current Cabibbo--Kobayashi--Maskawa angles, $\beta=22.0^\circ$ and
$\gamma=59.0^\circ$, our results for the mixing-induced parameter $S$ and
$\alpha_{\rm eff}$ differ from the measurements of the time-dependent CP
asymmetries in the decay $B^0\to a_1^\pm \pi^\mp$ at about the $3.7\sigma$
level. This puzzle may be resolved by using a larger $\gamma \gtrsim 80^\circ$.
For $a_1 K$ modes, the annihilation topologies give sizable contributions and
are sensitive to the first Gegenbauer moment of the leading-twist tensor
(chiral-odd) distribution amplitude of the $a_1$ meson. The $B\to a_1 K$
amplitudes resemble the corresponding $B\to \pi K$ ones very much. Taking the
ratios of corresponding CP-averaged $a_1 K$ and $\pi K$ branching ratios, we
can extract information relevant to the electroweak penguins and annihilations.
The existence of new-physics in the electroweak penguin sector and final state
interactions during decays can thus be explored.Comment: 20 pages, 1 figure, 4 tables, typos corrected, some discussions
added, version to appear in PR

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