Axion-like particles (ALPs) are a well-motivated extension to the standard model of particle physics, and X-ray observations of cluster-hosted AGN currently place the most stringent constraints on ...the ALP coupling to electromagnetism, \(g_{a \gamma}\), for very light ALPs (\(m_a\lesssim10^{-11}\) eV). We revisit limits obtained by Reynolds et al. (2020) using Chandra X-ray grating spectroscopy of NGC 1275, the central AGN in the Perseus cluster, examining the impact of the X-ray spectral model and magnetic field model. We also present a new publicly available code, ALPro, which we use to solve the ALP propagation problem. We discuss evidence for turbulent magnetic fields in Perseus and show that it can be important to resolve the magnetic field structure on scales below the coherence length. We re-analyse the NGC 1275 X-ray spectra using an improved data reduction and baseline spectral model. We find the limits are insensitive to whether a partially covering absorber is used in the fits. At low \(m_a\) (\(m_a\lesssim10^{-13}\) eV), we find marginally weaker limits on \(g_{a \gamma}\) (by \(0.1-0.3\) dex) with different magnetic field models, compared to Model B from Reynolds et al. (2020). A Gaussian random field (GRF) model designed to mimic \(\sim50\) kpc scale coherent structures also results in only slightly weaker limits. We conclude that the existing Model B limits are robust assuming that \(\beta_{\rm pl}\approx100\), and are insensitive to whether cell-based or GRF methods are used. However, astrophysical uncertainties regarding the strength and structure of cluster magnetic fields persist, motivating high sensitivity RM observations and tighter constraints on the radial profile of \(\beta_{\rm pl}\).
The human immunodeficiency virus (HIV) epidemic provides a rare opportunity to examine in detail the initial stages of a host‐pathogen co‐evolutionary struggle in humans. The genes encoding the human ...leukocyte antigen (HLA) class I molecules have a critical influence in the success or failure of the immune response against HIV. The particular HLA class I molecules expressed by each individual defines the type of cytotoxic T‐lymphocyte (CTL) response that is made against the virus. This chapter describes the role of HLA class I and the CTL response in controlling HIV replication, and discusses the extent to which HIV has already adapted to those HLA class I molecules and CTL responses that are most effective in viral suppression. It is evident that viral mutations that enable HIV to evade the CTL response are indeed already accumulating in populations where the selecting HLA molecules are highly prevalent, indicating the dynamic and shifting nature of the evolutionary interplay between HIV and human populations.
We report the detection of a transiting hot Neptune exoplanet orbiting TOI-824 (SCR J1448-5735), a nearby (d = 64 pc) K4V star, using data from the \textit{Transiting Exoplanet Survey Satellite} ...(TESS). The newly discovered planet has a radius, \(R_{\rm{p}}\) = 2.93 \(\pm\) 0.20 R\(_{\oplus}\), and an orbital period of 1.393 days. Radial velocity measurements using the Planet Finder Spectrograph (PFS) and the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph confirm the existence of the planet and we estimate its mass to be \(M_{\rm{p}}\) = 18.47 \(\pm\) 1.84 M\(_{\oplus}\). The planet's mean density is \(\rho_{\rm{p}}\) = 4.03\(^{+0.98}_{-0.78}\) g cm\(^{-3}\) making it more than twice as dense as Neptune. TOI-824 b's high equilibrium temperature makes the planet likely to have a cloud free atmosphere, and thus an excellent candidate for follow up atmospheric studies. The detectability of TOI-824 b's atmosphere from both ground and space is promising and could lead to the detailed characterization of the most irradiated, small planet at the edge of the hot Neptune desert that has retained its atmosphere to date.
Axion-Like Particles (ALPs) are well-motivated extensions of the Standard Model of Particle Physics and a generic prediction of some string theories. X-ray observations of bright Active Galactic ...Nuclei (AGN) hosted by rich clusters of galaxies are excellent probes of very-light ALPs, with masses \(\mathrm{log}(m_\mathrm{a}/\mathrm{eV}) < -12.0\). We evaluate the potential of future X-ray observatories, particularly \(Athena\) and the proposed \(AXIS\), to constrain ALPs via observations of cluster-hosted AGN, taking NGC 1275 in the Perseus cluster as our exemplar. Assuming perfect knowledge of instrument calibration, we show that a modest exposure (200-ks) of NGC 1275 by \(Athena\) permits us to exclude all photon-ALP couplings \(g_\mathrm{a\gamma} > 6.3 \times 10^{-14} \ {\mathrm{GeV}}^{-1}\) at the 95% level, as previously shown by \(Conlon \ et \ al. \ (2018)\), representing a factor of 10 improvement over current limits. We then proceed to assess the impact of realistic calibration uncertainties on the \(Athena\) projection by applying a standard \(Cash\) likelihood procedure, showing the projected constraints on \(g_\mathrm{a\gamma}\) weaken by a factor of 10 (back to the current most sensitive constraints). However, we show how the use of a deep neural network can disentangle the energy-dependent features induced by instrumental miscalibration and those induced by photon-ALP mixing, allowing us to recover most of the sensitivity to the ALP physics. In our explicit demonstration, the machine learning applied allows us to exclude \(g_\mathrm{a\gamma} > 2.0 \times 10^{-13} \ {\mathrm{GeV}}^{-1}\), complementing the projected constraints of next-generation ALP dark matter birefringent cavity searches for very-light ALPs. Finally, we show that a 200-ks \(AXIS\)/on-axis observation of NGC 1275 will tighten the current best constraints on very-light ALPs by a factor of 3.
PDF
