[Show abstract][Hide abstract]ABSTRACT: The WIMPs are considered one of the most favorable dark matter (DM) candidates, but as the upper bound on the interaction between DM and standard model (SM) particles obtained by the upgraded facilities for direct detection of DM gets lower and lower. Researchers turn their attention to search for less massive DM candidates, i.e. light dark matter of MeV scale. The recently measured anomalous transition in $^8$Be suggests that there exists a vectorial boson which may mediate the interaction between DM and SM particles. Based on this scenario, we combine the relevant cosmological data to constrain the mass range of DM, and have found that there exists a model parameter space where the requirements are satisfied, a range of $10.4 \lesssim m_{\phi} \lesssim 16.7 $ MeV for scalar DM, and $13.6 \lesssim m_{V} \lesssim 16.7$ MeV for vectorial DM is demanded. Then a possibility of directly detecting such light DM particles at the earth detector via the DM-electron scattering is briefly studied in this framework.
[Show abstract][Hide abstract]ABSTRACT: The QCD multipole expansion (QCDME) is based on quantum field theory and has been extensively applied to study transitions among and ψ family members. As it refers to non-perturbative QCD, however, it has only a certain application range. Even though it successfully explains the transition data among members of the (ψ) family, as Eichten indicates, beyond the production threshold of mediate states it fails to match data by several orders of magnitude. In this work, by studying a simple decay mode D*→ D + π0, where a pion may be emitted before D* transitions into D, we analyze the contribution of QCD multipole expansion. As the Dπ portal is open, the dominant contribution is an OZI-allowed process where a light quark-pair is excited out from vacuum, and its contribution can be evaluated by the 3P
0 model. Since direct pion emission is OZI-suppressed and violates isospin conservation, its contribution must be much smaller than the dominant one. By a careful calculation, we estimate that the QCDME contribution should be 3–4 orders smaller than the dominant contribution and this result can offer a quantitative interpretation for Eichten's statement.
Full-text available · Article · Jul 2016 · Chinese Physics C
[Show abstract][Hide abstract]ABSTRACT: We study the decay process of J/ψ → e+e− where the relatively clean electromagnetic (EM) transitions appear at leading order at tree level while the hadronic contributions only emerge via hadronic loop transitions. We include the low-lying scalar f0(980) and pseudoscalar η/η' as the dominant contributions in the evaluation of the hadronic loop contributions. It is found that the hadronic effects are negligible compared with the EM contributions. The decay width of J/ψ → e+e− is determined to be about 2.12 × 10−6 keV if there is no other leading mechanism contributing. This result will be tested by the BESIII experiment with a large J/ψ data sample.
Full-text available · Article · Jul 2016 · Chinese Physics C
[Show abstract][Hide abstract]ABSTRACT: Three-generation MSW effect in curved spacetime is studied and a brief discussion on the gravitational correction to the neutrino self-energy is given. The modified mixing parameters and corresponding conversion probabilities of neutrinos after traveling through celestial objects of constant densities are obtained. The method to distinguish between the normal hierarchy and inverted hierarchy is discussed in this framework. Due to the gravitational redshift of energy, in some extreme situations, the resonance energy of neutrinos might be shifted noticeably and the gravitational effect on the self-energy of neutrino becomes significant at the vicinities of spacetime singularities.
Full-text available · Article · Jun 2016 · Nuclear Physics B
[Show abstract][Hide abstract]ABSTRACT: In this work, we introduce an extra singlet pseudoscalar into the Type-III two Higgs doublet model (2HDM) which is supposed to solve a series of problems in the modern particle-cosmology. With existence of a light pseudoscalar, the excess measured at CMS and as well as the anomaly could be simultaneously explained within certain parameter spaces that can also tolerate the data on the flavor-violating processes and Higgs decay gained at LHC. Within the same parameter spaces, the DM relic abundance is well accounted. Moreover, the recently observed Galactic Center gamma ray excess (GCE) is proposed to realize through dark matter (DM) pair annihilations, and in this work, the scenario of the annihilation being mediated by the pseudoscalar is also addressed.
Full-text available · Article · Jun 2016 · Nuclear Physics B
[Show abstract][Hide abstract]ABSTRACT: The inner structures of the multiquark states are an interesting subject in hadron physics, generally they may be in tetraquark states which are composed of colored constituents, or in molecular states which are composed of two color singlets, or their mixtures. Therefore, the mechanisms which bind the constituents in a unique system and induce the multiquark states to decay would be different in those cases. In this work, using the quantum mechanics we analyze the dynamical mechanisms inducing decays of the tetraquarks where Y(4630) stands as an example for the study, we also comment on the molecular states without making numerical computations.
[Show abstract][Hide abstract]ABSTRACT: Several approximate equalities among the matrix elements of CKM and PMNS imply that hidden symmetries may exist and be common for both quark and neutrino sectors. The CP phase of the CKM matrix ($\delta_{\rm CKM}$) is involved in these equalities and can be investigated when these equalities turn into several equations. As we substitute those experimentally measured values of the three mixing angles into the equations for quarks, it is noted that one of the equations which holds exactly has a solution $\delta_{\rm CKM}=68.95^\circ$. That value accords with $(69.1^{+2.02}_{-3.85})^\circ$ determined from available data. Generalizing the scenario to the lepton sector, the same equality determines the leptonic CP phase $\delta_{\rm PMNS}$ to be $ 276.10^\circ$. Thus we predict the value of $\delta_{\rm PMNS}$ from the equation. So far there is no direct measurement on $\delta_{\rm PMNS}$ yet, but a recent analysis based on the neutrino oscillation data prefers the phase close to $270^\circ$.
[Show abstract][Hide abstract]ABSTRACT: A resonance Y(4630) at the invariant mass spectrum of ΛcΛ¯c observed by the Belle Collaboration triggers a hot discussion about its inner structure. Since it preferably decays into two charmed baryons ΛcΛ¯c, it is tempting to conjecture that it is a tetraquark. Because the dominant decay portal Y(4630)→ΛcΛ¯c is close to the energy threshold, the final state interactions should be significant. Other bayonic and/or mesonic final states resulted from the ΛcΛ¯c interactions may be sizable to be measured in the future experiments. In this work we calculate the branching ratios of the Y(4630) decays into pp¯, D(*)+D(*)−, π+π−, and K+K−, which are induced by the ΛcΛ¯c rescattering. The resultant decay patterns will be tested by the future experiments and the consistency degree with the data composes a valuable probe for the tetraquark conjecture.
[Show abstract][Hide abstract]ABSTRACT: At the invariant mass spectrum of $h_c\pi^\pm$ a new resonance $Z_c(4020)$
has been observed, however the previously confirmed $Z_c(3900)$ does not show
up at this channel. In this paper we assume that $Z_c(3900)$ and $Z_c(4020)$
are molecular states of $D\bar D^*(D^{*} \bar D)$ and $D^*\bar D^*$
respectively, then we calculate the transition rates of $Z_c(3900)\to h_c+\pi$
and $Z_c(4020)\to h_c+\pi$ in the light front model. Our results show that the
partial width of $Z_c(3900)\to h_c+\pi$ is only three times smaller than that
of $Z_c(4020)\to h_c+\pi$. $Z_c(4020)$ seems to be a molecular state, so if
$Z_c(3900)$ is also a molecular state it should be observed in the portal
$e^+e^-\to h_c\pi^\pm$ as long as the database is sufficiently large, by
contrary if the future more precise measurements still cannot find $Z_c(3900)$
at $h_c\pi^\pm$ channel, the molecular assignment to $Z_c(3900)$ should be
ruled out.
Full-text available · Article · Jan 2016 · European Physical Journal C
[Show abstract][Hide abstract]ABSTRACT: The structures of the $X,Y,Z$ exotic states which recently are experimentally
observed one after another, have composed a challenge to our understanding of
the fundamental principles in the hadron physics and the relevant study will
definitely shed light on the concerned physics. Generally the four-quark states
might be in a molecular state or teraquark or their mixture. In this work, we
adopt the suggestion that $Y(4630)$ is a charmonium-like tetraquark made of a
diquark and an anti-diquark. If it is true, its favorable decay mode should be
$Y(4360)$ decaying into an open-charm baryon pair, since such a transition
occurs via strong interaction and is super-OZI-allowed. In this work, we
calculate the decay width of $Y(4630)\to\Lambda^+_c\Lambda^-_c$ in the
framework of the quark pair creation (QPC) model. The numerical results suggest
that the $Y(4630)$ state is a radially excited state.
Full-text available · Article · Jan 2016 · European Physical Journal C
[Show abstract][Hide abstract]ABSTRACT: In a supersymmetric extension of the standard model where baryon and lepton
numbers are local gauge symmetries, we analyze the signals of decay channels
$\Phi\rightarrow gg$, $\Phi\rightarrow\gamma\gamma$ and $\Phi\rightarrow
\bar{t}t,\;VV\;(V=Z,\;W)$ with the CP-odd scalar $\Phi=A_{_B}^0$ mass around
$750\;{\rm GeV}$ which is observed at the LHC at a center of mass energy of
$13\;{\rm TeV}$. Adopting some assumptions on relevant parameter space, the
CP-odd scalar $A_{_B}^0$ can account for the experimental data on $750\;{\rm
GeV}$ diphoton excess from ATLAS and CMS naturally.
[Show abstract][Hide abstract]ABSTRACT: We propose that the unified Fano-like interference picture applies to
$e^+e^-\to \pi^+\pi^- J/\psi$ and $e^+e^-\to \pi^+\pi^- \psi(3686)$, where
$Y(4260)$ and $Y(4360)$ are observed, respectively, to provide a reasonable
interpretation of the asymmetric lineshapes of $Y(4260)$ and $Y(4360)$
structures. Moreover, the Fano-like interference induces an extra broad
structure $Y(4008)$ in $e^+e^-\to \pi^+\pi^- J/\psi$ as a companion peak to
$Y(4260)$. Three charmonium-like states $Y(4008)$, $Y(4260)$ and $Y(4360)$
observed in $e^+e^-$ annihilation processes are not genuine resonances. Under
this scenario, it is well explained why $Y(4008)$, $Y(4260)$ and $Y(4360)$ are
absent in the experimental data of the $R$ value scan and missing in open-charm
decay channels. Although the present work presents the a typical application of
the Fano-like interference in the particle physics at the lower energy region,
we have reason to believe that the Fano-like phenomena may exist in other
processes such as $e^+e^-\to \pi^+\pi^-\psi(3770)$ and $e^+e^-\to K^+K^-
J/\psi$, which will be accessible at BESIII and forthcoming BelleII.
[Show abstract][Hide abstract]ABSTRACT: We study the decay process of $J/\psi\rightarrow e^+e^- \phi$ where the
relatively clean electromagnetic (EM) transitions appear at leading order at
tree level while the hadronic contributions only emerge via hadronic loop
transitions. We include the low-lying scalar $f_0(980)$ and pseudoscalar
$\eta/\eta'$ as the dominant contributions in the evaluation of the hadronic
loop contributions. It is found that the hadronic effects are negligible
comparing with the EM contributions. The decay width of $J/\psi\rightarrow
e^+e^- \phi$ is determined to be about $2.12\times 10^{-6}$ keV if there is no
any other leading mechanism contributing, and this result will be tested by the
BESIII experiment with a large data sample of $J/\psi$.
[Show abstract][Hide abstract]ABSTRACT: The QCD multipole expansion (QCDME) is based on the quantum field theory, so
should be more reliable. However, on another aspect, it refers to the
non-perturbative QCD , so that has a certain application range. Even though it
successfully explains the data of transition among members of the $\Upsilon$
($\psi$) family, as Eichten indicates, beyond the production threshold of
mediate states it fails to meet data by several orders. In this work, by
studying a simple decay mode $D^*\to D+\pi^0$, where a pion may be emitted
before $D^*$ transiting into $D$, we analyze the contribution of QCD multipole
expansion. Whereas as the $D\pi$ portal is open, the dominant contribution is
an OZI allowed process where a light quark-pair is excited out from vacuum and
its contribution can be evaluated by the $^3P_0$ model. Since the direct pion
emission is a process which is OZI suppressed and violates the isospin
conservation, its contribution must be much smaller than the dominant one. By a
careful calculation, we may quantitatively estimate how small the QCDME
contribution should be and offer a quantitative interpretation for Eichten's
statement.
[Show abstract][Hide abstract]ABSTRACT: In this work, we introduce an extra pseudoscalar into the Type-III two-Higgs
doublet model (2HDM). In the framework of the extended 2HDM, the
$h\rightarrow\mu\tau$ excess measured at CMS and $(g-2)_{\mu}$ anomaly can be
simultaneously explained within a parameter space which is not ruled out by the
flavor-violating process $\tau\rightarrow\mu\gamma$. Moreover, existence of the
pseudo-scalar provides an opportunity to interpret the Galactic Center gamma
ray excess(GCE) which might be caused by dark matter(DM) pair annihilations. It
is also noted that to meet the observed DM relic density, other DM annihilation
channels are needed.
[Show abstract][Hide abstract]ABSTRACT: The discovery of the new resonances $P_c(4380)$ and $P_c(4450)$ indeed opens
a new page for hadron physics. They are identified as the long-expected
pentaquarks. Now the Gell-Mann's quark model is complete. On the other aspect,
the light multiquark exotic states are not stable, so cannot exist individually
but mix with the regular structures with the same quantum numbers. With heavy
flavors which play an important role to stabilize the systems, the multiquark
states are able to exist. The allegation is not only true for the exotic mesons
which have already been experimentally observed and named as $X$, $Y$, $Z$
particles, but also for the baryons which have $Q\bar Q qqq$ structures.
Further experimental and theoretical research should be pursued in the future.
[Show abstract][Hide abstract]ABSTRACT: Investigating the CKM matrix in different parametrization schemes, it is
noticed that those schemes can be divided into a few groups where the sine
values of the CP phase for each group are approximately equal. Using those
relations, several approximate equalities among the elements of CKM matrix are
established. Assuming them to be exact, there are infinite numbers of solutions
and by choosing special values for the free parameters in those solutions,
several textures presented in literature are obtained. The case can also be
generalized to the PMNS matrix for the lepton sector. In parallel, several
mixing textures are also derived by using presumed symmetries, amazingly, some
of their forms are the same as what we obtained, but not all. It hints
existence of a hidden symmetry which is broken in the practical world. The
nature makes its own selection on the underlying symmetry and the way to break
it, while we just guess what it is.
Full-text available · Article · Jun 2015 · Chinese Physics C
[Show abstract][Hide abstract]ABSTRACT: The approximately symmetric form of the PMNS matrix suggests that there could
exist a hidden symmetry which makes the PMNS matrix different from the CKM
matrix for quarks. In literature, all the proposed fully symmetric textures
exhibit an explicit $\mu-\tau$ symmetry in addition to other symmetries which
may be different for various textures. Observing obvious deviations of the
practical PMNS matrix elements from those in the symmetric textures, there must
be a mechanism to distort the symmetry. It might be due to existence of light
sterile neutrinos. In this work, we study the case of the Tribimaximal texture
and propose that its apparent symmetry disappears due to existence of a sterile
neutrino. We observe that introducing just one sterile neutrino is still not
sufficient to recover the data, thus a slight $\mu-\tau$ symmetry breaking is
also needed. By considering those factors, we obtain the PMNS matrix elements
which are consistent with data within the experimental tolerance.