Updated constraints on new physics in rare charm decays

Motivated by recent experimental results on charm physics we investigate implications of the updated constraints of new physics in rare charm meson decays. We first reconsider effects of the MSSM in $c\to u \gamma$ constrained by the recent experimental evidence on $\Delta m_D$ and find, that due to the dominance of long distance physics, $D \to V \gamma$ decay rates cannot be modified by MSSM contributions. Then we consider effects of the extra heavy up vector-like quark models on the decay spectrum of $D^+ \to \pi^+ l^+ l^-$ and $D_s^+ \to K^+ l^+ l^-$ decays. We find a possibility for the tiny increase of the differential decay rate in the region of large dilepton mass. The R-parity violating supersymmetric model can also modify short distance dynamics in $c \to u l^+ l^-$ decays. We constrain relevant parameters using current upper bound on the $D^+ \to \pi^+ l^+ l^-$ decay rate and investigate impact of that constraint on the $D_s^+ \to K^+ l^+ l^-$ differential decay dilepton distribution. Present bounds still allow small modification of the standard model differential decay rate distribution.Comment: 15 pages, 4 figure

The controversy in the γγ→ρρ\gamma\gamma\to\rho\rho process: potential scattering or qqqˉqˉqq\bar{q}\bar{q} resonance ?

The $\gamma\gamma\to\rho^0\rho^0\to 4 \pi$ reaction shows a broad peak at 1.5 GeV in the $(J^P,J_z)=(2^+,2)$ channel which has no counterpart in the $\rho^+\rho^-$ channel. This "resonance" is considered as a candidate for a $qq\bar q\bar q$ state in the "s-channel". We show, however, that it can also be explained by potential scattering of $\rho^0\rho^0$ via the $\sigma$- exchange in the "t-channel".Comment: 12 pages, latex, 3 postscript figures, to appear in Zeitschrift fur Physi

On the mass differences between the scalar and pseudoscalar heavy-light mesons

We discuss the recent experimental observation which suggested that the mass difference between the scalar and pseudoscalar heavy-light mesons is larger for the non-strange states than for the strange ones. After computing the chiral corrections in the heavy quark limit we show that, contrary to experiment, the mass difference in the non-strange case should be smaller.Comment: 10 pages, 2 figure

B --> pi and B --> K transitions in partially quenched chiral perturbation theory

We study the properties of the B-->pi and B-->K transition form factors in partially quenched QCD by using the approach of partially quenched chiral perturbation theory combined with the static heavy quark limit. We show that the form factors change almost linearly when varying the value of the sea quark mass, whereas the dependence on the valence quark mass contains both the standard and chirally divergent (quenched) logarithms. A simple strategy for the chiral extrapolations in the lattice studies with Nsea=2 is suggested. It consists of the linear extrapolations from the realistically accessible quark masses, first in the sea and then in the valence quark mass. From the present approach, we estimate the uncertainty induced by such extrapolations to be within 5%.Comment: Published versio

B-->pi and B-->K transitions in standard and quenched chiral perturbation theory

We study the effects of chiral logs on the heavy-->light pseudoscalar meson transition form factors by using standard and quenched chiral perturbation theory combined with the static heavy quark limit. The resulting expressions are used to indicate the size of uncertainties due to the use of the quenched approximation in the current lattice studies. They may also be used to assess the size of systematic uncertainties induced by missing chiral log terms in extrapolating toward the physical pion mass. We also provide the coefficient multiplying the quenched chiral log, which may be useful if the quenched lattice studies are performed with very light mesons.Comment: 33 pages, 8 PostScript figures, version to appear in PR

Toward the quark mass dependence of Tcc+T_{cc}^+ from lattice QCD

The $DD^*$ scattering phase shifts in the $T_{cc}^+ = ccbar{u}bar{d}$ channel are extracted from lattice QCD for five different charm quark masses and a fixed light-quark mass corresponding to $m_{pi} simeq$ 280  MeV. The phase shifts are analyzed employing two approaches: effective range expansion and Lippmann-Schwinger equation derived in the effective field theory. In the latter case, the results imply an attraction at short range parametrized by contact terms and a slight repulsion at long range mediated by one-pion exchange with $m_{pi} > m_{D^*}-m_D$. The poles in the amplitude across the complex energy plane are extracted and their trajectories are discussed as the charm quark mass is varied. Two complex conjugate poles corresponding to a resonance below threshold are found for $m_c$ close to the physical value. They turn into a pair of virtual states at the largest $m_c$ studied. With further increasing $m_c$, one virtual pole representing $T_{cc}^+$ is expected to move towards the two-body threshold and turn into a bound state. The light-quark mass dependence of the $T_{cc}^+$ pole is briefly discussed using the data on $DD^*$ scattering from other lattice collaborations