arXiv subjects

Marcel Golz

Publications and source records attributed to Marcel Golz.

17 recordsLinked to original sources

arXiv2023

Model-independent analysis of $b\to d$ processes

We perform a model-independent analysis of $|Δb|=|Δd|=1$ processes to test the standard model and probe flavor patterns of new physics. Constraints on Wilson coefficients are obtained from global fits to $B^+ \to π^+ \,μ^+μ^-$, $B^0_s\to \bar{K}^{*0}\, μ^+μ^-$, $B^0\toμ^+μ^-$, and radiative $B \to X_d \,γ$ decays data. The fits are consistent with the standard model but leave sizable room for new physics. Besides higher-statistics measurements and more data in theory-friendly bins of the dilepton mass, further complementary observables such as angular distributions of $B_s^0 \to \bar{K}^{*0}\,\ell^+ \ell^-$, $B \to ρ\,\ell^+ \ell^-$ or the baryonic modes $Ξ_b \to Σ\,\ell^+ \ell^-$, $Ω_b^- \to Ξ^- \, \ell^+ \ell^-$ are necessary to resolve the significant degeneracy in the fit for the semileptonic four-fermion operators. Assuming minimal quark flavor violation, the $b \to s$ global fit implies tight constraints on the $b \to d$ couplings, and hence allows to test this paradigm with improved data. Another benefit from $|Δb|=|Δd|=1$ processes is to shed light on the $B$-anomalies in $|Δb|=|Δs|=1$ modes from a new angle. Specifically, studies of lepton flavor-specific and dineutrino modes are informative on the lepton flavor structure. Rare $b \to d \, \ell \ell, ν\bar ν$ decays can be studied at high luminosity flavor facilities LHCb, Belle II, and a future $Z$-factory.

hep-ph↗

arXiv2022

Probing for New Physics with Rare Charm Baryon ($Λ_c$, $Ξ_c$, $Ω_c$) Decays

We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized $Λ_c \to p \ell^+ \ell^-$, $\ell=e, μ$ decays, and study the new physics sensitivities. We find that the longitudinal dilepton polarization fraction $F_L$ is sensitive to electromagnetic dipole couplings $C_{7}^{(\prime)}$, and to the right-handed 4-fermion vector coupling $C_{9}^\prime$. The forward-backward asymmetry, $A_{\rm FB}$, due to the GIM-suppression a standard model null test already, probes the left-handed axialvector 4-fermion coupling $C_{10}$; its CP-asymmetry, $A_{\rm FB}^{\rm CP}$, probes CP-violating phases in $C_{10}$. Physics beyond the standard model can induce branching ratios of dineutrino modes $Λ_c \to p ν\bar ν$ up to a few times $10^{-5}$, and one order of magnitude smaller if lepton flavor universality is assumed, while standard model rates are negligible. Charged lepton flavor violation allows for striking signals into $e^\pm μ^\mp$ final states, up to $10^{-6}$ branching ratios model-independently, and up to order $10^{-8}$ in leptoquark models. Related three-body baryon decays $Ξ_c \to Σ\ell \ell$, $Ξ_c \to Λ\ell \ell$ and $Ω_c \to Ξ\ell \ell$ offer similar opportunities to test the standard model with $|Δc|=|Δu|=1$ transitions.

hep-ph↗

arXiv2022

Null test BSM searches with rare charm baryon decays

Rare $\vert Δc \vert=\vert Δu \vert=1$ processes uniquely probe flavor in the Standard Model and beyond from the up-type quark sector. Opportunities to search for BSM physics in charm arise from the severe GIM suppression which kills SM contributions to leptonic axial-vector contributions and suppresses CP violation. Semileptonic decays of charmed hadrons offer a variety of clean null test observables, featuring new physics effects which are even enhanced by resonance contributions. In particular, angular observables in three- and self-analyzing four-body baryon decays, such as $Λ_c\to p \ell^+\ell^-$ and $Ξ_c^+\toΣ^+(\to pπ^0)\ell^+\ell^-$, $Ξ_c^0\toΛ^0\,(\to p π^-)\ell^+\ell^-$ and $Ω_c^0\toΞ^0\,(\to Λ^{0} π^0)\ell^+\ell^-$ disentangle possible new physics effects in electromagnetic dipole couplings $C_7^{(\prime)}$ and (axial-)vector 4-fermion ones $C^{(\prime)}_{9\,(10)}$. There is sensitivity to BSM couplings as small as $\sim 0.01$.

hep-ph↗

arXiv2022

Lepton universality and lepton flavor conservation tests with dineutrino modes

$SU(2)_L$-invariance links charged dilepton and dineutrino couplings. Phenomenological implications are worked out for flavor changing neutral currents involving strange, charm, beauty and top quark transitions in a model-independent way. We put forward novel tests of lepton universality and lepton flavor conservation in $|Δc|= |Δu|=1$ and $|Δb|= |Δq|=1$, $q=d,s$, transitions suitable for the experiments Belle II and BES III. Single top production plus dileptons uniquely probes semileptonic four-fermion $|Δt|= |Δq'|=1$, $q'=u,c$, couplings and further study at the LHC is encouraged. Tests with single top production associated with dileptons and missing energy are suitable for study at future $e^+ e^-$ or muon colliders.

hep-ph↗

arXiv2022

Pinning down $|Δc|=|Δu|=1$ couplings with rare charm baryon decays

We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, $Ξ_c^+\toΣ^+\,(\to pπ^0)\ell^+\ell^-$, $Ξ_c^0\toΛ^0\,(\to p π^-)\ell^+\ell^-$ and $Ω_c^0\toΞ^0\,(\to Λ^{0} π^0)\ell^+\ell^-$. Such self-analyzing decay chains allow for seven additional observables compared to three-body decays such as $Λ_c \to p \ell^+ \ell^-$, with different sensitivities to the $|Δc|=|Δu|=1$ weak couplings. Opportunities to test the standard model in $c \to u$ transitions with standard model null tests and other angular observables are worked out. We show that a joint model-independent analysis of the leptonic $A_{\text{FB}}^\ell$, hadronic $A_{\text{FB}}^{\text{H}}$, and combined forward-backward asymmetry $A_{\text{FB}}^{\ell\text{H}}$ together with the fraction of longitudinally produced leptons, $F_L$, is able to pin down the dipole couplings $C_{7},C^\prime_{7}$ and the semileptonic (axial-) vector ones $C_{10},C^\prime_{9},C^\prime_{10}$. $A_{\text{FB}}^{\text{H}}$ is also accessible with dineutrino $c \to u ν\bar ν$ modes and probes right-handed currents.

hep-ph↗

arXiv2021

Interplay of dineutrino modes with semileptonic rare $\boldsymbol{B}$-decays

We present a systematic global analysis of dineutrino modes $b \to q \,ν\bar ν$, $q=d,s$, and charged dilepton $b \to q \,\ell^+ \ell^-$ transitions. We derive improved or even entirely new limits on dineutrino branching ratios including decays $B^0 \to (K^0 , X_s)\, ν\bar ν$, $B_s \to ϕ\,ν\bar ν$ and $B^0 \to (π^0, ρ^0)\, ν\bar ν$ from dineutrino modes which presently are best constrained: $B^+ \to (K^+,π^+, ρ^+) \,ν\bar ν$ and $B^0 \to K^{*0} \,ν\bar ν$. Using SMEFT we obtain new flavor constraints from the dineutrino modes, which are stronger than the corresponding ones from charged dilepton rare $b$-decay or Drell-Yan data, for $e τ$ and $ττ$ final states, as well as for $μτ$ ones in $b \to s$ processes. The method also allows to put novel constraints on semileptonic four-fermion operators with top quarks. Implications for ditau modes $b \to s \, τ^+ τ^-$ and $b \to d \, τ^+ τ^-$ are worked out. Furthermore, the interplay between dineutrinos and charged dileptons allows for concrete, novel tests of lepton universality in rare $B$-decays. Performing a global fit to $b \to s \,μ^+ μ^-, \,s γ$ transitions we find that lepton universality predicts the ratio of the $B^0 \to K^{*0} \,ν\bar ν$ to $B^0 \to K^0 \,ν\bar ν$ ($B^+ \to K^+ \,ν\bar ν$) branching fractions to be within 1.7 to 2.6 (1.6 to 2.4) at $1\,σ$, a region that includes the standard model, and that can be narrowed with improved charged dilepton data. There is sizable room outside this region where universality is broken and that can be probed with the Belle II experiment. Using results of a fit to $B^0 \to μ^+ μ^-$, $B^0_s\to \bar{K}^{\ast 0}\,μ^+μ^-$ and $ B^+ \to π^+\, μ^+ μ^-$ data we obtain an analogous relation for $|Δb|=|Δd|=1$ transitions.

hep-ph↗

arXiv2021

Dineutrino modes probing lepton flavor violation

$SU(2)_L$-invariance links charged dilepton $\bar q\,q^\prime\,\ell^+\,\ell^-$ and dineutrino $\bar q\, q^\prime\, \barν\,ν$ couplings. This connection can be established using the Standard Model Effective Field Theory framework, and allows to perform complementary experimental tests of lepton universality and charged lepton flavor conservation with flavor-summed dineutrino observables. We present its phenomenological implications for the branching ratios of rare charm decays $c\to u\,ν\,\barν$ and rare $B$ decays $b\to s\,\barν\,ν$ decays.

hep-ph↗

arXiv2021

Null test searches for BSM physics with rare charm decays

Semileptonic Flavor Changing Neutral Current decays of charmed hadrons uniquely probe the up-sector of the Standard Model. Clean null test observables, such as CP-asymmetries, lepton-universality ratios, missing energy modes, lepton flavor violating modes and angular observables can be studied in a variety of charmed meson and baryon modes. An overview of null test opportunities with rare charm decays is presented and similarities and complementarities of different modes are worked out.

hep-ph↗

arXiv2021

Physics reach of ${D}_{(s)}\to π(K) \ell\ell$ and other charming null test opportunities

We discuss possibilities to test physics beyond the Standard Model in $\vertΔc\vert=\vertΔu\vert= 1$ semileptonic, hadronic and missing energy decay modes. Clean null test observables such as angular observables, CP-asymmetries and lepton universality tests are presented and model-independent correlations as well as details within flavorful, anomaly-free $Z^\prime$ models are worked out.

hep-ph↗

arXiv2021

Theoretical and experimental status of rare charm decays

Rare charm decays offer the unique possibility to explore flavour-changing neutral-currents in the up-sector within the Standard Model and beyond. Due to the lack of effective methods to reliably describe its low energy dynamics, rare charm decays have been considered as less promising for long. However, this lack does not exclude the possibility to perform promising searches for New Physics per se, but a different philosophy of work is required. Exact or approximate symmetries of the Standard Model allow to construct clean null-test observables, yielding an excellent road to the discovery of New Physics, complementing the existing studies in the down-sector. In this review, we summarize the theoretical and experimental status of rare charm $|Δc|=|Δu|=1$ transitions, as well as opportunities for current and future experiments such as LHCb, Belle II, BES III, the FCC-ee and proposed tau-charm factories. We also use the most recent experimental results to report updated limits on lepton-flavour conserving and lepton-flavour violating Wilson coefficients.

hep-ph↗

arXiv2021

Rare charm $\boldsymbol{c\to u\,ν\barν}$ dineutrino null tests for $\boldsymbol{e^+e^-}$-machines

Rare $|Δc|=|Δu|=1$ transitions into dineutrinos are strongly GIM-suppressed and constitute excellent null tests of the standard model. While branching ratios of $D \to P \,ν\bar ν$, $D \to P^+ P^- \, ν\bar ν$, $P=π, K$, baryonic $Λ_c^+ \to p \,ν\bar ν$, and $Ξ_c^+ \to Σ^+ \, ν\bar ν$ and inclusive $D \to X ν\bar ν$ decays are experimentally unconstrained, signals of new physics can be just around the corner. We provide model-independent upper limits on branching ratios reaching few $\times 10^{-5}$ in the most general case of arbitrary lepton flavor structure, $\sim 10^{-5}$ for scenarios with charged lepton conservation and few $\times 10^{-6}$ assuming lepton universality. We also give upper limits in $Z^\prime$ and leptoquark models. The presence of light right-handed neutrinos can affect these limits, a possibility that can occur for lepton number violation at a TeV, and that can be excluded with an improved bound on $\mathcal{B}(D^0 \to \text{invisibles})$ at the level of $\sim 10^{-6}$, about two orders of magnitude better than the present one. Signatures of $c \to u ν\bar ν$ modes contain missing energy and are suited for experimental searches at $e^+ e^-$-facilities, such as BES III, Belle II and future $e^+ e^-$-colliders, such as the FCC-ee running at the $Z$.

hep-ph↗

arXiv2021

The New Physics Reach of Null Tests with $D \to π\ell \ell$ and $D_s \to K \ell \ell $ Decays

$|Δc|=|Δu|=1$ processes are unique probes of flavor physics in the up-sector within and beyond the Standard Model (SM). SM tests with rare semileptonic charm meson decays are based on an approximate CP--symmetry, a superior GIM--mechanism, angular distributions, lepton-universality and lepton flavor conservation. We analyze the complete set of null test observables in $D \to π\ell \ell^{(\prime)}$ and $D_s \to K \ell \ell^{(\prime)}$ decays, $\ell^{(\prime)}=e, μ$, and find large room for new physics safely above the SM contribution. We identify signatures of supersymmetry, leptoquarks and anomaly-free $U(1)^\prime$-models with generation-dependent charges, for which we provide explicit examples. $Z^\prime$-effects in $c \to u \ell \ell^{(\prime)}$ transitions can be sizable if both left-handed and right-handed couplings to quarks are present.

hep-ph↗

arXiv2020

Exploiting CP-asymmetries in rare charm decays

We analyze patterns from CP-violating new physics (NP) in hadronic and semileptonic rare charm $\vert Δc \vert=\vert Δu\vert=1$ transitions. Observation of direct CP-violation in hadronic decays, as in $ΔA_{\text{CP}}$, provides opportunities for $c \to u \,\ell^+ \ell^-$, $\ell=e,μ$ transitions, and vice versa. For the concrete case of flavorful, anomaly-free $Z^\prime$-models a NP-interpretation of $ΔA_{\text{CP}}$ suggests measurable CP-asymmetries in semileptonic decays such as $D \to π\, \ell^+ \ell^-$ or $D \to ππ\, \ell^+ \ell^-$. Conversely, an observation of CP-violation in $c \to u\, e^+ e^-$ or $c \to u\, μ^+ μ^-$ decays supports a NP--interpretation of $ΔA_{\text{CP}}$. Flavorful $U(1)^\prime$-extensions provide explicit U--spin and isospin breaking which can be probed in patterns of hadronic decays of charm mesons. We work out signatures for CP-asymmetries in $D^0 \to π^+ π^-$, $D^0 \to K^+ K^-$ and $D^0 \to π^0 π^0$, $D^+ \to π^+ π^0$ decays, which can be probed in the future at LHCb and Belle II and provide further informative cross checks.

hep-ph↗

arXiv2018

Dodgson polynomial identities

Dodgson polynomials appear in Schwinger parametric Feynman integrals and are closely related to the well known Kirchhoff (or first Symanzik) polynomial. In this article a new combinatorial interpretation and a generalisation of Dodgson polynomials are provided. This leads to two new identities that relate large sums of products of Dodgson polynomials to a much simpler expression involving powers of the Kirchhoff polynomial. These identities can be applied to the parametric integrand for quantum electrodynamics, simplifying it significantly. This is worked out here in detail on the example of superficially renormalised photon propagator Feynman graphs, but works much more generally.

math-ph↗

arXiv2018

Contraction of Dirac matrices via chord diagrams

Chord diagrams and combinatorics of word algebras are used to model products of Dirac matrices, their traces, and contractions. A simple formula for the result of arbitrary contractions is derived, simplifying and extending an old contraction algorithm due to Kahane. This formula is then used to express the Schwinger parametric integrand of a QED Feynman integral in a much simplified form, with the entire internal tensor structure eliminated. Possible next steps for further simplification, including a specific conjecture, are discussed.

math-ph↗

arXiv2017

Graphical functions in parametric space

Graphical functions are positive functions on the punctured complex plane $\mathbb{C}\setminus\{0,1\}$ which arise in quantum field theory. We generalize a parametric integral representation for graphical functions due to Lam, Lebrun and Nakanishi, which implies the real analyticity of graphical functions. Moreover we prove a formula that relates graphical functions of planar dual graphs.

math-ph↗

arXiv2017

New graph polynomials in parametric QED Feynman integrals

In recent years enormous progress has been made in perturbative quantum field theory by applying methods of algebraic geometry to parametric Feynman integrals for scalar theories. The transition to gauge theories is complicated not only by the fact that their parametric integrand is much larger and more involved. It is, moreover, only implicitly given as the result of certain differential operators applied to the scalar integrand $\exp(-Φ_Γ/Ψ_Γ)$, where $Ψ_Γ$ and $Φ_Γ$ are the Kirchhoff and Symanzik polynomials of the Feynman graph $Γ$. In the case of quantum electrodynamics we find that the full parametric integrand inherits a rich combinatorial structure from $Ψ_Γ$ and $Φ_Γ$. In the end, it can be expressed explicitly as a sum over products of new types of graph polynomials which have a combinatoric interpretation via simple cycle subgraphs of $Γ$.

math-ph↗