arXiv subjects

Nejc Kosnik

Publications and source records attributed to Nejc Kosnik.

21 records · Page 2Linked to original sources

arXiv2008

Leptoquarks in FCNC charm decays

Recently it was noticed that among many scenarios of new physics leptoquarks might compensate for the disagreement between the lattice and experimental results for the charmed strange meson decay constant. The leptoquarks might modify also the flavor changing neutral current charm decays. In this study we investigate impact of the scalar leptoquark with electric charge -1/3 on the dilepton invariant mass distribution in the D^+ --> pi^+ mu^+ mu^- decay and on the branching ratios of the D^0 --> mu^+ mu^- using the existing experimental results.

hep-ph↗

arXiv2007

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 $c\to u γ$ constrained by the recent experimental evidence on $Δm_D$ and find, that due to the dominance of long distance physics, $D \to V γ$ 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 $D^+ \to π^+ l^+ l^-$ 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 $D^+ \to π^+ l^+ l^-$ 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.

hep-ph↗

arXiv2006

b to d d s bar transition and constraints on new physics in B^- decays

The b to d d s bar transition gives extremely small branching ratios within the standard model, thus providing an appropriate ground for testing new physics. Using renormalization group technique we determine the Wilson coefficients and the mixing of the operators which contribute to the b to d d s bar transition. We consider contributions to this decay mode from the supersymmetric standard model with and without R-parity, as well as from a model with an additional neutral Z' gauge boson. Using Belle and BaBar upper bounds for the B^- to pi^- pi^- K^+ branching ratio we constrain contributions of these new physics scenarios. Then we calculate branching ratios for two- and three-body nonleptonic B^- meson decays driven by the b to d d s transition, which might be experimentally accessible.

hep-ph↗