Nuclear Theory·nucl-th

Friday·December 18, 2020

6 papers—3 primary·3 cross-listed

04
Leading-order QED radiative corrections to timelike Compton scattering on the proton
Matthias Heller🇩🇪 · Niklas Keil🇩🇪 · Marc Vanderhaeghen🇩🇪
We evaluate the leading-order QED radiative corrections to the timelike Compton scattering (TCS) process $γ p \to l^{-} l^{+} p$ . We study these corrections in two energy regimes using different models for the TCS amplitude. In the low-energy regime we calculate the contribution due to the proton and its lowest-energy excitation, the $Δ (1232)$ resonance. In the high-energy near-forward kinematical regime we calculate the TCS amplitude in a handbag approach in terms of Generalized Parton Distributions (GPDs). On the level of cross sections we find the QED radiative corrections to be in the $5 - 10%$ range in the low-energy regime and around $20%$ in the high-energy regime. We show that in both the di-lepton forward-backward asymmetry as well as in the photon beam helicity asymmetry these corrections nearly cancel out, making them gold-plated observables to extract the real and imaginary parts of the TCS amplitude. We demonstrate in particular the sensitivity of these asymmetries on GPD parameterizations for a recent CLAS12@JLab TCS experiment.
↳ hep-phnucl-thPRD(2021)·6 citations
05
Probing the nuclear equation of state from the existence of a $\sim 2.6 M_{⊙}$ neutron star: the GW190814 puzzle
A. Kanakis-Pegios🇬🇷 · P.S. Koliogiannis🇬🇷 · Ch.C. Moustakidis🇬🇷
On August 14, 2019, the LIGO/Virgo collaboration observed a compact object with mass $\sim 2.5 9_{- 0.09}^{+ 0.08} M_{⊙}$ , as a component of a system where the main companion was a black hole with mass $\sim 23 M_{⊙}$ . A scientific debate initiated concerning the identification of the low mass component, as it falls into the neutron star - black hole mass gap. The understanding of the nature of GW190814 event will offer rich information concerning open issues, the speed of sound and the possible phase transition into other degrees of freedom. In the present work, we made an effort to probe the nuclear equation of state along with the GW190814 event. Firstly, we examine possible constraints on the nuclear equation of state inferred from the consideration that the low mass companion is a slow or rapidly rotating neutron star. In this case, the role of the upper bounds on the speed of sound is revealed, in connection with the dense nuclear matter properties. Secondly, we systematically study the tidal deformability of a possible high mass candidate existing as an individual star or as a component one in a binary neutron star system. As the tidal deformability and radius are quantities very sensitive on the neutron star equation of state, they are excellent counters on dense matter properties. We conjecture that similar isolated neutron stars or systems may exist in the Universe and their possible future observation will shed light on the maximum neutron star mass problem.
↳ astro-ph.HEgr-qcnucl-thSymmetry(2021)·54 citations
06
Searching for Lepton Flavour (Universality) Violation and Collider Signals from a Singly-Charged Scalar Singlet
Andreas Crivellin🇨🇭 · Fiona Kirk🇨🇭 · Claudio Andrea Manzari🇨🇭 · Luca Panizzi🇸🇪
In recent years, evidence for lepton flavour universality violation beyond the Standard Model has been accumulated. In this context, a singly charged $S U (2)_{L}$ singlet scalar ( $ϕ^{\pm}$ ) is very interesting, as it can only have flavour off-diagonal couplings to neutrinos and charged leptons, therefore necessarily violating lepton flavour (universality). In fact, it gives a (necessarily constructive) tree-level effect in $ℓ \to ℓ^{'} ν ν$ processes, while contributing to charged lepton flavour violating only at the loop-level. Therefore, it can provide a common explanation of the hints for new physics in $τ \to μν ν / τ (μ) \to e ν ν$ and of the Cabibbo Angle Anomaly. Such an explanation predicts $Br [τ \to e γ]$ to be of the order of a few times $1 0^{- 11}$ while $Br [τ \to e μμ]$ can be of the order of $1 0^{- 9}$ for order one couplings and therefore in the reach of forthcoming experiments. Furthermore, we derive a {novel} coupling-independent lower limit on the scalar mass of $\approx 200$ GeV by recasting LHC slepton searches. In the scenario preferred by low energy precision data, the lower limit is even strengthened to $\approx 300$ GeV, showing the complementary between LHC searches and flavour observables. Furthermore, we point out that this model can be tested by reinterpreting DM mono-photon searches at future $e^{+} e^{-}$ colliders.
↳ hep-phhep-exnucl-exnucl-thPRD(2021)·66 citations

Affiliations

first authorsco-authorsvia INSPIRE

Leading-order QED radiative corrections to timelike Compton scattering on the proton

Probing the nuclear equation of state from the existence of a ∼2.6 M⊙​ neutron star: the GW190814 puzzle

Searching for Lepton Flavour (Universality) Violation and Collider Signals from a Singly-Charged Scalar Singlet

Affiliations

Probing the nuclear equation of state from the existence of a $\sim 2.6 M_{⊙}$ neutron star: the GW190814 puzzle