# particles

 hep-ph updates on arXiv.org High Energy Physics - Phenomenology (hep-ph) updates on the arXiv.org e-print archive Cosmological Constraints on Invisible Neutrino Decays Revisited. (arXiv:1907.05425v1 [hep-ph]) Authors: Miguel Escudero, Malcolm Fairbairn Neutrinos could decay. Invisible neutrino decay modes are difficult to target at laboratory experiments, and current bounds on such decays from solar neutrino and neutrino oscillation experiments are somewhat weak. It has been known for some time that Cosmology can serve as a powerful probe of invisible neutrino decays. In this work, we show that in order for Big Bang Nucleosynthesis to be successful, the invisible neutrino decay lifetime should be $\tau_\nu > 10^{-3}\,\text{s}$. We revisit Cosmic Microwave Background constraints on invisible neutrino decays, and by using the latest Planck observations we find that neutrino lifetimes $\tau_\nu < (1.2-0.3)\times 10^{9}\,\text{s} \, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$ are excluded at $95\%$ CL. We show that this bound is robust to modifications of the cosmological model, in particular that it is independent of the presence of dark radiation. We find that typical invisible neutrino decay modes with rates $\tau_\nu < 10^{5}\,\text{s}\, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$ are disfavoured at more than $5\,\sigma$ with respect to $\Lambda$CDM given the latest Planck CMB observations. Finally, we show that when including high-$\ell$ Planck polarization data, neutrino lifetimes $\tau_\nu = (2-14)\times 10^{9}\,\text{s} \, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$ are mildly preferred -- with a 1-2 $\sigma$ significance -- over neutrinos being stable. Polarizability of the nucleon. (arXiv:1907.05434v1 [hep-ph]) Authors: Martin Schumacher The status of the experimental and theoretical investigations on the polarizabilities of the nucleon is presented. This includes a confirmation of the validity of the previously introduced recommended values of the polarizabilities [1,2]. It is shown that the only meaningful approach to a prediction of the polarizabilities is obtained from the nonsubtracted dispersion theory, where the appropriate degrees of freedom taken from other precise experimental data are taken in account. The present values of the recommended polarizabilities are $\alpha_p= 12.0 \pm 0.5$, $\beta_p= 1.9 \mp 0.5$, $\alpha_n= 12.6 \pm 1.2$, $\beta_n= 2.6 \mp 1.2$ in units of $10^{-4}$fm$^3$ and $\gamma^{(p)}_\pi= -36.4 \pm 1.5$, $\gamma^{(n)}_\pi =+58.6 \pm 4.0$, $\gamma^{(p)}_0=-0.58 \pm 0.20$, $\gamma^{(n)}_0= +0.38\pm 0.22$ in units of $10^{-4}$fm$^4$. Correlations between azimuthal anisotropy Fourier harmonics in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$~TeV in the HYDJET++ and AMPT models. (arXiv:1907.05450v1 [nucl-th]) Correlations between azimuthal anisotropy Fourier harmonics $v_{n}$ ($n = 2, 3, 4$) are studied using the events from PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$~TeV generated by the HYDJET++ and AMPT models, and compared to the corresponding experimental results obtained by the ATLAS Collaboration. The Fourier harmonics $v_{n}$ are measured over a wide centrality range using the two-particle azimuthal correlation method. The slopes of the $v_{2}$--$v_{3}$ correlation from both models are in a good agreement with the ATLAS data. The HYDJET++ model predicts a stronger slope for the $v_{2}$--$v_{4}$ and $v_{3}$--$v_{4}$ correlations than the ones experimentally measured, while the results from the AMPT model are in a rather good agreement with the experimental results. In contrast to the HYDJET++ predictions, the AMPT model predicts a boomerang-like shape in the structure of the correlations as found in the experimental data. On the Cottingham formula and the electromagnetic contribution to the proton-neutron mass splitting. (arXiv:1907.05459v1 [nucl-th]) Authors: Andre Walker-Loud The excess mass of the neutron over the proton arises from two sources within the Standard Model, electromagnetism and the splitting of the down and up quark masses. The Cottingham Formula provides a means of determining the QED corrections from the forward Compton Amplitude, but this is challenged by the need for a subtraction function and the mixing of the QED and QCD (electro-weak) effects. I review the present understanding of the Cottingham Formula, including a discussion on the development of the formula, its renormalization which induces the mixing of QED and QCD effects, and the necessary modeling of the subtraction function that must be done to arrive a numerical prediction. I summarize the Regge Model originally proposed by Gasser and Leutwyler and I also review the proposed model by Walker-Loud, Carlson and Miller, which is an interpolation function between the low and high $Q^2$ regimes, both of which are anchored by rigorous theoretical underpinnings, for which I argue a more reliable theoretical uncertainty estimate can be obtained. Violation of the Kluberg-Stern--Zuber theorem in SCET. (arXiv:1907.05463v1 [hep-ph]) A classic result, originally due to Kluberg-Stern and Zuber, states that operators that vanish by the classical equation of motion (eom) do not mix into "physical" operators. Here we show that and explain why this result does not hold in soft-collinear effective theory (SCET) for the renormalization of power-suppressed operators. We calculate the non-vanishing mixing of eom operators for the simplest case of $N$-jet operators with a single collinear field in every direction. The result implies that---for the computation of the anomalous dimension but not for on-shell matrix elements---there exists a preferred set of fields that must be used to reproduce the infrared singularities of QCD scattering amplitudes. We identify these fields and explain their relation to the gauge-invariant SCET Lagrangian. Further checks reveal another generic property of SCET beyond leading power, which will be relevant to resummation at the next-to-leading logarithmic level, the divergence of convolution integrals with the hard matching coefficients. We propose an operator solution that allows to consistently renormalize such divergences. Electroweak corrections to the fermionic decays of heavy Higgs states. (arXiv:1907.05468v1 [hep-ph]) Authors: Florian Domingo, Sebastian Paßehr Extensions of the Standard Model often come with additional, possibly electroweakly charged Higgs states, the prototypal example being the Two-Higgs-Doublet Model. While collider phenomenology does not exclude the possibility for some of these new scalar fields to be light, it is relatively natural to consider masses in the multi-TeV range, in which case the only remaining light Higgs boson automatically receives SM-like properties. The appearance of a hierarchy between the new-physics states and the electroweak scale then leads to sizable electroweak corrections, e. g. in the decays of the heavy Higgs bosons, which are dominated by effects of infrared type, namely Sudakov logarithms. Such radiative contributions obviously affect the two-body decays, but should also be paired with the radiation of electroweak gauge bosons (or lighter Higgs bosons) for a consistent picture at the one-loop order. Resummation of the leading terms is also relatively easy to achieve. We re-visit these questions in the specific case of the fermionic decays of heavy Higgs particles in the Next-to-Minimal Supersymmetric Standard Model, in particular pointing out the consequences of the three-body final states for the branching ratios of the heavy scalars. Astrophysical limits on very light axion-like particles from Chandra grating spectroscopy of NGC 1275. (arXiv:1907.05475v1 [hep-ph]) Axions and axion-like particles (ALPs) are a well motivated extension of the Standard Model and are generic in String Theory. The X-ray transparency of the magnetized intracluster medium (ICM) in galaxy clusters is a powerful probe of very light ALPs (masses \$0