Pionic Dark Matter

We study a phenomenological model where the lightest dark matter (DM) particles are the pseudo-Goldstone excitations associated with a spontaneously broken symmetry, and transforming linearly with respect to an unbroken group H. For definiteness we take H = SU(N) and assume the Goldstone particles are bosons; in parallel with QCD, we refer to these particles as dark-matter pions. This scenario is in contrast to the common assumption that DM fields transform linearly under the full symmetry of the model. We illustrate the formalism by treating in detail the case of H = SU(2), in particular we calculate all the interactions relevant for the Boltzmann equations, which we solve numerically; we also derive approximate analytic solutions and show their consistency with the numerical results. We then compare the results with the constraints derived from the cold DM and direct detection experiments and derive the corresponding restrictions on the model parameters.Comment: 35 pages, 15 figure

Pion form factor analysis using NLO analytic perturbation theory

I present results for the pion's electromagnetic form factor in the spacelike region, which implement the most advanced perturbative information currently available for this observable in conjunction with a pion distribution amplitude that agrees with the CLEO data on the pion-photon transition form factor at the $1\sigma$ level. I show that using for the running strong coupling and its powers their analytic versions in the sense of Shirkov and Solovtsov, the obtained predictions become insensitive to the renormalization scheme and scale setting adopted. Joining the hard contribution with the soft part on account of local duality and respecting the Ward identity at $Q^2=0$, the agreement with the available experimental data, including expectations from planned experiments at JLab, is remarkable both in trend and magnitude. I also comment on Sudakov resummation within the analytic approach.Comment: 5 pages, 3 figures embedded; uses espcrc2.tex. Invited talk presented at QCD04, 5-9 July 2004, Montpellier, Franc

Seeking the CP-odd Higgs via h→ηc,bℓ+ℓ−h\rightarrow \eta_{c,b}\ell^+\ell^-

We show that the decay rates of the Higgs boson to a pseudoscalar quarkonium and a pair of leptons, $h\to P\ell^+\ell^-$ ($P\in\{\eta_c,\eta_b\}$), can be substantially enhanced in a scenario with two Higgs doublets with a softly broken $\mathbb{Z}_2$ symmetry (2HDM) when the CP-odd Higgs A is light, i.e. $m_A\lesssim m_h$. Depending on the type of 2HDM the enhancement of $\mathcal{B}(h\to \eta_{c,b}\tau^+\tau^-)$ with respect to its Standard Model value can be an order of magnitude larger, i.e. $\mathcal{O}(10^{-6}\div10^{-5})$. The decays $h\to P\ell^+\ell^-$ could therefore provide an efficient channel to investigate the presence of a light CP-odd Higgs $A$ and help to disentangle among various 2HDM scenarios.Comment: 19 pages, 6 figure

B, Bs -> K form factors: an update of light-cone sum rule results

We present an improved QCD light-cone sum rule (LCSR) calculation of the B -> K and Bs -> K form factors, by including SU(3)-symmetry breaking corrections. We use recently updated K-meson distribution amplitudes which incorporate the complete SU(3)-breaking structure. By applying the method of the direct integration in the complex plane, which is presented in a detail, the analytical extraction of the imaginary parts of LCSR hard-scattering amplitudes becomes unnecessary and therefore the complexity of the calculation is greatly reduced. The values obtained for the relevant B_{(s)} -> K form factors are as follows: f^+_{BK}(0)= 0.36^{+0.05}_{-0.04}, f^+_{B_sK}(0)= 0.30^{+0.04}_{-0.03} and f^T_{BK}(0)= 0.38\pm 0.05, f^T_{B_sK}(0)= 0.30\pm 0.05. By comparing with the B -> pi form factors extracted recently by the same method, we find the following SU(3) violation among the B -> light form factors: f^+_{BK}(0)/f^+_{B\pi}(0) = 1.38^{+0.11}_{-0.10}, f^+_{B_sK}(0)/f^+_{B\pi}(0) = 1.15^{+0.17}_{-0.09}, f^T_{BK}(0)/f^T_{B\pi}(0) = 1.49^{+0.18}_{-0.06} and f^T_{B_sK}(0)/f^T_{B\pi}(0) = 1.17^{+0.15}_{-0.11}.Comment: 14 pages, 9 figures, some figures and discussions added; version to appear in PR

K -> pi gamma decays and space-time noncommutativity

We propose the K -> pi gamma decay mode as a signature of the violation of the Lorentz invariance and the appearance of new physics via space-time noncommutativity.Comment: 3 pages, 1 figure included, version to appear in Phys. Rev.