arXiv subjects

Miša Toman

Publications and source records attributed to Miša Toman.

3 recordsLinked to original sources

arXiv2026

Spin Correlations in Dark Photon Searches

We investigate the spin correlations between production and decay in the process where dark photons $A'$ are produced in pseudoscalar meson decays, for example, $π^0, η\to γA'$, and then decay to fermion pairs, $A' \to f \bar{f}$. This process is the focus of many experimental searches, but spin correlations are typically ignored. We derive analytic results that allow us to quickly scan parameter space and quantify the error made in neglecting spin correlations. In particular, we define a discrepancy parameter and find that this parameter is always less than $\frac{1}{6\sqrt{3}} \approx 9.6\%$, which provides a rough measure of the size of spin correlation effects. However, these effects may be enhanced or suppressed by cuts in realistic experimental analyses, and so we also consider two representative examples, including current FASER analyses and possible future searches at SHiP. We find that the effects of spin correlations are negligible for existing FASER analyses, but can significantly reduce event rates at upcoming SHiP searches.

hep-ph↗

arXiv2026

The X17 with Chiral Couplings

In recent years, the ATOMKI collaboration has performed a series of measurements of excited nuclei, observing a resonant excess of electron-positron pairs at large opening angles compared to the Standard Model prediction. The excess has been hypothesized to be due to the production of a new spin-1 or spin-0 particle, X17, with a mass of about 17 MeV. Recently, the PADME experiment has reported an excess in the $e^+e^-$ cross section at center-of-mass energies near 17 MeV, perhaps further hinting at the existence of a new state. Studies of the spin-1 case have hitherto focused on either vector {\em or} axial-vector couplings to quarks and leptons, whereas UV theories more naturally produce {\em both} vector and axial-vector (\textit{i.e.} chiral) couplings, analogous to the Standard Model weak interactions. We consider the ATOMKI anomalies in the context of an $X$ with chiral couplings to quarks and explore the parameter space that can explain the ATOMKI anomalies, contrasting them with experimental constraints. We find that it is possible to accommodate the reported ATOMKI signals. However, the $99\%$ CL region is in tension with null results from searches for atomic parity violation and direct searches for new low mass physics coupled to electrons. This tension is found to be driven by the magnitude of the reported excess in the transition of $^{12}{\rm C}(17.23)$, which drives the best-fit region towards excluded couplings.

hep-ph↗

arXiv2022

$L_\infty$-algebra of braided electrodynamics

Using the recently developed formalism of braided noncommutative field theory, we construct an explicit example of braided electrodynamics, that is, a noncommutative $U(1)$ gauge theory coupled to a Dirac fermion. We construct the braided $L_\infty$-algebra of this field theory and apply the formalism to obtain the braided equations of motion, action functional and conserved matter current. The braided deformation leads to a modification of the charge conservation. Finally, the Feynman integral appearing in the one-loop contribution to the vacuum polarization diagram is calculated. There are no non-planar diagrams, but the UV/IR mixing appears nevertheless. We comment on this unexpected result.

hep-th↗