Prospects of discovering new physics in rare charm decays

Abstract:We investigate the ability of the S 3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S 3 leptoquark with quantum numbers (3, 3, 1/3) naturally emerges in the context of an SU(5) GUT model without any conflict with the stringent limits from observed nucleon stability. Scalar leptoquark S 3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both R K ( * ) and R D ( * ) . We quantify this suitability with numerical fits to a plethora of relevant flavor observables. The proposed SU(5) model calls for a second leptoquark state, i.e.,R 2 with quantum numbers (3, 2, 1/6), if one is to generate gauge coupling unification and neutrino mass. We accordingly include it in our study to investigateR 2 's ability to offset adverse effects of S 3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S 3 to τ leptons are preferred. We furthermore identify B → K ( * )ν ν as the most sensitive channel to probe the preferred region of parameter space. Large couplings of S 3 to τ leptons are finally confronted with the experimental searches for τ final states at the Large Hadron Collider. These searches comprise a study of decay products of the leptoquark pair production, as well as, and more importantly, an analysis of the high-mass τ τ final states.

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“…[80]. We learn that the ensuing bound y sµ 0.5(m S 3 /TeV) from rare decays is weaker than the abovementioned bound from semileptonic decays.…”

Section: Decaysmentioning

confidence: 90%

The role of the S 3 GUT leptoquark in flavor universality and collider searches

Doršner

Fajfer

Faroughy

et al. 2017

J. High Energ. Phys.

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104

110

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“…Nevertheless, there have been a number of phenomenological studies on the new-physics (NP) sensitivities of rare charm decays, including radiative and rare semileptonic D-meson decays induced by c → uγ and c → u + − transitions, see e.g. [4][5][6][7][8][9][10][11][12][13][14][15][16].…”

Section: Jhep08(2017)105mentioning

confidence: 99%

“…A straightforward approach, which has already been extensively used in the past [7,9,12,13,15], assumes that the long-distance hadronic effects are completely dominated by the lowest-lying narrow vector states (ρ, ω, φ etc.) which are then modelled by Breit-Wigner resonances.…”

Section: Jhep08(2017)105mentioning

confidence: 99%

“…In this way one can still look for new-physics scenarios with large Wilson coefficients which are not excluded by current exprerimental data, see e.g. the discussion in the recent literature [13,14]. (To a certain extent, this also applies to the purely radiative decays D → ργ which have recently been seen by the Belle experiment [57].…”

Section: Jhep08(2017)105mentioning

confidence: 99%

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D → ρℓ + ℓ − decays in the QCD factorization approach

Feldmann¹,

Müller²,

Seidel³

2017

J. High Energ. Phys.

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We consider rare semileptonic decays of a heavy D-meson into a light vector meson in the framework of QCD factorization. In contrast to the corresponding B-meson decays, the naive factorization hypothesis does not even serve as a first approximation. Rather, the decay amplitudes appear to be dominated by non-factorizable dynamics, e.g. through annihilation topologies, which are particularly sensitive to long-distance hadronic contributions. We therefore pay particular attention to intermediate vector-meson resonances appearing in quark-loop and annihilation topologies. Compared to the analogous B-meson decays, we identify a number of effects that result in very large theoretical uncertainties for differential decay rates. Some of these effects are found to cancel in the ratio of partially integrated decay rates for transversely and longitudinally polarized ρ mesons. On the phenomenological side this implies a very limited potential to constrain physics beyond the Standard Model by means of these decays.

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“…weaken these constraints, and following [37], we find these constraints are subdominant to those derived from mixing. We briefly note the potential importance of a dimension 6 operator beyond those considered in eq.…”

Section: Jhep01(2017)054mentioning

confidence: 51%

Naturalness from a composite top?

Pierce¹,

Zhao²

2017

J. High Energ. Phys.

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We consider a theory with composite top quarks but an elementary Higgs boson. The hierarchy problem can be solved by supplementing TeV scale top compositeness with either supersymmetry or Higgs compositeness appearing at the multi-TeV scale. The Higgs boson couples to uncolored partons within the top quark. We study how this approach can give rise to a novel screening effect that suppresses production of the colored top partners at the LHC. Strong constraints arise from Z tobb, as well potentially from flavor physics. Independent of flavor considerations, current constraints imply a compositeness scale TeV; this implies that the model is likely tuned at the percent level. Four top quark production at the LHC is a smoking-gun probe of this scenario. New CP violation in D meson mixing is also possible.

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Prospects of discovering new physics in rare charm decays

Cited by 78 publications

References 50 publications

The role of the S 3 GUT leptoquark in flavor universality and collider searches

The role of the S 3 GUT leptoquark in flavor universality and collider searches

D → ρℓ + ℓ − decays in the QCD factorization approach

Naturalness from a composite top?

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