Digging into Axion Physics with (Baby)IAXO

Dark matter searches have been ongoing for three decades; the lack of a positive discovery of the main candidate, the WIMP, after dedicated efforts, has put axions and axion-like particles in the spotlight. The three main techniques employed to search for them complement each other well in covering a wide range in the parameter space defined by the axion decay constant and the axion mass. The International AXion Observatory (IAXO) is an international collaboration planning to build the fourth generation axion helioscope, with an unparalleled expected sensitivity and discovery potential. The distinguishing characteristic of IAXO is that it will feature a magnet that is designed to maximise the relevant parameters in sensitivity and which will be equipped with X-ray focusing devices and detectors that have been developed for axion physics. In this paper, we review aspects that motivate IAXO and its prototype, BabyIAXO, in the axion, and ALPs landscape. As part of this Special Issue, some emphasis is given on Spanish participation in the project, of which CAPA (Centro de Astropartículas y Física de Altas Energías of the Universidad de Zaragoza) is a strong promoter.

Integrating morphologic and molecular histopathological features through whole slide image registration and deep learning

Background Modern molecular pathology workflows in neuro-oncology heavily rely on the integration of morphologic and immunohistochemical patterns for analysis, classification, and prognostication. However, despite the recent emergence of digital pathology platforms and artificial intelligence-driven computational image analysis tools, automating the integration of histomorphologic information found across these multiple studies is challenged by large files sizes of whole slide images (WSIs) and shifts/rotations in tissue sections introduced during slide preparation. Methods To address this, we develop a workflow that couples different computer vision tools including scale-invariant feature transform (SIFT) and deep learning to efficiently align and integrate histopathological information found across multiple independent studies. We highlight the utility and automation potential of this workflow in the molecular subclassification and discovery of previously unappreciated spatial patterns in diffuse gliomas. Results First, we show how a SIFT-driven computer vision workflow was effective at automated WSI alignment in a cohort of 107 randomly selected surgical neuropathology cases (97/107 (91%) showing appropriate matches, AUC = 0.96). This alignment allows our AI-driven diagnostic workflow to not only differentiate different brain tumor types, but also integrate and carry out molecular subclassification of diffuse gliomas using relevant immunohistochemical biomarkers (IDH1-R132H, ATRX). To highlight the discovery potential of this workflow, we also examined spatial distributions of tumors showing heterogenous expression of the proliferation marker MIB1 and Olig2. This analysis helped uncovered an interesting and unappreciated association of Olig2 positive and proliferative areas in some gliomas (r = 0.62). Conclusion This efficient neuropathologist-inspired workflow provides a generalizable approach to help automate a variety of advanced immunohistochemically compatible diagnostic and discovery exercises in surgical neuropathology and neuro-oncology.

$$ t\overline{t}t\overline{t} $$ signatures through the lens of color-octet scalars

We reinterpret two recent LHC searches for events containing four top quarks $$ \left(t\overline{t}t\overline{t}\right) $$ t t ¯ t t ¯ in the context of supersymmetric models with Dirac gauginos and color-octet scalars (sgluons). We explore whether sgluon contributions to the four-top production cross section $$ \sigma \left( pp\to t\overline{t}t\overline{t}\right) $$ σ pp → t t ¯ t t ¯ can accommodate an excess of four-top events recently reported by the ATLAS collaboration. We also study constraints on these models from an ATLAS search for new phenomena with high jet multiplicity and significant missing transverse energy $$ \left({E}_{\mathrm{T}}^{\mathrm{miss}}\right) $$ E T miss sensitive to signals with four top quarks. We find that these two analyses provide complementary constraints, with the jets + $$ {E}_{\mathrm{T}}^{\mathrm{miss}} $$ E T miss search exceeding the four-top cross section measurement in sensitivity for sgluons heavier than about 800 GeV. We ultimately find that either a scalar or a pseudoscalar sgluon can currently fit the ATLAS excess in a range of reasonable benchmark scenarios, though a pseudoscalar in minimal Dirac gaugino models is ruled out. We finally offer sensitivity projections for these analyses at the HL-LHC, mapping the 5σ discovery potential in sgluon parameter space and computing exclusion limits at 95% CL in scenarios where no excess is found.

Z lepton flavour violation as a probe for new physics at future $$e^+e^-$$ colliders

In this work we assess the potential of discovering new physics by searching for lepton-flavour-violating (LFV) decays of the Z boson, $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j , at the proposed circular $$e^+e^-$$ e + e - colliders CEPC and FCC-ee. Both projects plan to run at the Z-pole as a “Tera Z factory”, i.e., collecting $${\mathcal {O}}\left( 10^{12} \right) $$ O 10 12 Z decays. In order to discuss the discovery potential in a model-independent way, we revisit the LFV Z decays in the context of the Standard Model effective field theory and study the indirect constraints from LFV $$\mu $$ μ and $$\tau $$ τ decays on the operators that can induce $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j . We find that, while the $$Z\rightarrow \mu e$$ Z → μ e rates are beyond the expected sensitivities, a Tera Z factory is promising for $$Z\rightarrow \tau \ell $$ Z → τ ℓ decays, probing New Physics at the same level of future low-energy LFV observables.

Testing the $$R_{D^{(*)}}$$ anomaly at the LHeC

B-Physics anomalies have recently raised renewed interest in leptoquarks, predicted in several theoretical frameworks. Under simplifying but conservative assumptions, we show that the current limits from LHC searches together with the requirement to explain the observed value for $$R_{D^{(*)}}$$ R D ( ∗ ) constrain the $$R_2$$ R 2 leptoquark mass to be in the range of $$800 \le m_{R_2} \le 1000$$ 800 ≤ m R 2 ≤ 1000 GeV. We study the search for $$R_2$$ R 2 at the LHeC via its resonance in the $$b\tau $$ b τ final state by performing a cut-and-count analysis of the signal and the dominant Standard Model backgrounds. We find that the LHeC has an excellent discovery potential for the $$R_2$$ R 2 leptoquark even for couplings to the first generation as small as $${\mathcal {O}}(10^{-2})$$ O ( 10 - 2 ) .

Dijet impact factor in DIS at next-to-leading order in the Color Glass Condensate

We compute the next-to-leading order impact factor for inclusive dijet production in deeply inelastic electron-nucleus scattering at small xBj. Our computation, performed in the framework of the Color Glass Condensate effective field theory, includes all real and virtual contributions in the gluon shock wave background of all-twist lightlike Wilson line correlators. We demonstrate explicitly that the rapidity evolution of these correlators, to leading logarithmic accuracy, is described by the JIMWLK Hamiltonian. When combined with the next-to-leading order JIMWLK Hamiltonian, our results for the impact factor improve the accuracy of the inclusive dijet cross-section to $$ \mathcal{O} $$ O ($$ {\alpha}_s^2 $$ α s 2 ln(xf/xBj)), where xf is a rapidity factorization scale. These results are an essential ingredient in assessing the discovery potential of inclusive dijets to uncover the physics of gluon saturation at the Electron-Ion Collider.

The Large Hadron–Electron Collider at the HL-LHC

The Large Hadron–Electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy-recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High-Luminosity Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron–proton and proton–proton operations. This report represents an update to the LHeC’s conceptual design report (CDR), published in 2012. It comprises new results on the parton structure of the proton and heavier nuclei, QCD dynamics, and electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of lepton–nucleus scattering by several orders of magnitude. Due to its enhanced luminosity and large energy and the cleanliness of the final hadronic states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, this report contains a detailed updated design for the energy-recovery electron linac (ERL), including a new lattice, magnet and superconducting radio-frequency technology, and further components. Challenges of energy recovery are described, and the lower-energy, high-current, three-turn ERL facility, PERLE at Orsay, is presented, which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution, and calibration goals that arise from the Higgs and parton-density-function physics programmes. This paper also presents novel results for the Future Circular Collider in electron–hadron (FCC-eh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies.

A new and improved IceCube point source analysis

The IceCube Neutrino Observatory, a cubic kilometer scale Cherenkov detector deployed in the deep ice at the geographic South Pole, investigates extreme astrophysical phenomena by studying the corresponding high-energy neutrino signal. Its discovery of a diffuse flux of astrophysical neutrinos with energies up to the PeV scale in 2013 has triggered a vast effort to identify the mostly unknown sources of these high energy neutrinos. Here, we present a new IceCube point-source search that improves the accuracy of the statistical analysis, especially at energies of a few TeV and below. The new approach is based on multidimensional kernel density estimation for the probability density functions and new estimators for the observables, namely the reconstructed energy and the estimated angular uncertainty on the reconstructed arrival direction. The more accurate analysis provides an improvement in discovery potential up to ∼30% over previous works for hard spectrum sources.

Searching for leptoquarks at future muon colliders

A high energy muon collider can provide new and complementary discovery potential to the LHC or future hadron colliders. Leptoquarks are a motivated class of exotic new physics models, with distinct production channels at hadron and lepton machines. We study a vector leptoquark model at a muon collider with $$ \sqrt{s} $$ s = 3, 14 TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe leptoquark masses up to an order of magnitude beyond $$ \sqrt{s} $$ s with perturbative couplings. Additionally, we can also probe regions of parameter space unavailable to flavor experiments. In particular, all of the parameter space of interest to explain recent low-energy anomalies in B meson decays would be covered even by a $$ \sqrt{s} $$ s = 3 TeV collider.

Probing the nature of black holes: Deep in the mHz gravitational-wave sky

Black holes are unique among astrophysical sources: they are the simplest macroscopic objects in the Universe, and they are extraordinary in terms of their ability to convert energy into electromagnetic and gravitational radiation. Our capacity to probe their nature is limited by the sensitivity of our detectors. The LIGO/Virgo interferometers are the gravitational-wave equivalent of Galileo’s telescope. The first few detections represent the beginning of a long journey of exploration. At the current pace of technological progress, it is reasonable to expect that the gravitational-wave detectors available in the 2035-2050s will be formidable tools to explore these fascinating objects in the cosmos, and space-based detectors with peak sensitivities in the mHz band represent one class of such tools. These detectors have a staggering discovery potential, and they will address fundamental open questions in physics and astronomy. Are astrophysical black holes adequately described by general relativity? Do we have empirical evidence for event horizons? Can black holes provide a glimpse into quantum gravity, or reveal a classical breakdown of Einstein’s gravity? How and when did black holes form, and how do they grow? Are there new long-range interactions or fields in our Universe, potentially related to dark matter and dark energy or a more fundamental description of gravitation? Precision tests of black hole spacetimes with mHz-band gravitational-wave detectors will probe general relativity and fundamental physics in previously inaccessible regimes, and allow us to address some of these fundamental issues in our current understanding of nature.