Alan S. Cornell

We study quasinormal modes (QNMs) of a minimally coupled massless scalar field on four-dimensional Schwarzschild–anti-de Sitter (SAdS) black holes using a Chebyshev spectral method. After compactifying the exterior domain, the radial problem is formulated as a quadratic matrix pencil in the dimensionless frequency. For the standard Dirichlet, or vanishing-field, boundary condition at the conformal AdS boundary, we reproduce the known scalar spectra across small, intermediate, and large black holes, including long overtone sequences and the expected approach to pure-AdS normal modes in the small black hole limit. We also impose a one-parameter relation between the slow and fast asymptotic coefficients. For a massless scalar in four dimensions, the slow branch lies outside the standard finite canonical energy domain. Because we neither construct a renormalized variational principle nor prove well-posedness of an evolution containing this branch, we present only the formal spectrum of the deformed radial problem. Each non-Dirichlet value examined yields an additional eigenvalue with positive imaginary part and hence, an exponentially growing separated formal mode. This does not establish a physical instability of the standard scalar theory. The interpolation parameter is representation-dependent. In a black-hole-independent conformal coordinate, the corresponding response coupling scales with the cube of the dimensionless horizon radius, so equal intermediate parameter values for different black-hole sizes do not represent the same boundary coupling.

The five-dimensional minimal supersymmetric standard model (5D MSSM) provides an attractive framework in which power-law renormalization group evolution naturally generates a sizeable trilinear stop coupling, allowing the observed Higgs boson mass to be reproduced without requiring too heavy a supersymmetric spectra. In this work we present a comprehensive two-loop analysis of the 5D MSSM, deriving the complete renormalization group equations governing the gauge, Yukawa and soft supersymmetry-breaking sectors and examining the perturbative consistency of the theory. Particular attention is given to the ultraviolet behavior of the model, where we demonstrate that the potentially dangerous leading two-loop contributions cancel as a consequence of the underlying N = 2 supersymmetry, leaving a well-behaved perturbative expansion. Building upon this framework, we compute the radiatively corrected Higgs effective potential including the complete Kaluza-Klein (KK) contributions through KK resummation, and investigate the resulting implications for the Higgs sector. The phenomenological viability of the model is subsequently explored through detailed numerical studies of the Higgs boson mass, electroweak precision observables, Higgs coupling modifiers and signal strengths, allowing constraints on the compactification scale and supersymmetric parameter space to be established. We find that the inclusion of the two-loop corrections preserves the characteristic power-law behavior of the five-dimensional theory while yielding a phenomenologically viable parameter space consistent with current collider and precision measurements. Furthermore, as the KK tower provides the dominant correction to the Higgs quartic coupling, raising m h to 125 GeV, over the viable parameter space, the effective Higgs couplings remain close to their Standard Model values, showing a strong decoupling of the heavy KK modes.

We study the massive scalar quasinormal-mode spectral problem on a Schwarzschild background using an extended Chebyshev spectral method. The massive dispersion relation has a two-sheeted analytic structure, which we uniformize before discretization. This converts the radial problem into a seventh-degree polynomial eigenvalue problem while incorporating the quasinormal-mode boundary conditions at the horizon and spatial infinity. The method yields stable spectra for low multipoles, high overtones, and frequencies on both sides of the nominal mass threshold, including regimes in which Wentzel-Kramers-Brillouin and continued-fraction approaches become difficult to apply. For complex frequencies, the far-field behavior cannot be classified from the real part of the frequency alone, but depends on the complex wave number and its Riemann sheet. We also identify stable families of purely imaginary roots with approximately uniform spacing in their damping rates, whose physical interpretation remains open. The Schwarzschild scalar problem is intended as a controlled benchmark for massive-field quasinormal-mode calculations rather than as a direct model of tensorial Kerr ringdown.

A bstract: Flavourful extensions of the Standard Model aimed at explaining its fermionic mass structure typically rely on symmetries, broken at high-energy scales far beyond the reach of foreseeable direct collider searches. We illustrate, using a SU(2) flavour gauge group, that the breaking of these symmetries up to scales as high as 10 ⁷ GeV could generate a gravitational wave signal potentially observable by future observatories. We use dimensional reduction techniques to obtain the finite-temperature effective potential and study the possible first-order phase transitions. We match these transitions to steady-state hydrodynamical solutions in order to determine the corresponding gravitational-wave spectra. We observe that order-one gauge couplings are always required for a first-order phase transition to occur. On the other hand, adding leptoquarks (as an example of particles that are typically present in a complete flavour theory) significantly extends the testable parameter space. We find excellent prospects at the Einstein Telescope for future gravitational-wave detection of flavoured SU(2) early-universe phase transitions.

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

The nature of the PhD has shifted dramatically in recent times in accordance with the broadening of perspectives on the purposes of the qualification. This study considers the impact of this shift, highlighting the implications of changing student motivations on the PhD acculturation process, graduate identity formation, and the effectiveness of supervision practices in Science, Technology, Engineering, and Mathematics (STEM) disciplines. The study design is based on an overarching qualitative research enquiry into factors influencing supervision practice, where the perspectives and experiences of different supervisors were collated from semi-structured group interviews. We draw on Berry’s Model of Acculturation to analyse the roles and interplay of motivation and culture in relation to PhD graduate identity formation, and we examine the implications thereof for effective supervision. The study reveals the multifaceted dimensions of the acculturation process within the context of PhD supervision, viz., students’ motivations and identities, experiences and perceptions of supervisors, and cultural norms in the STEM community of practice. We demonstrate the shifts along these dimensions affecting PhD enculturation, showing how the alignment and discordance between student and supervisor may lead to assimilation, integration, marginalisation, and separation. This study contributes to increasing the body of research on doctoral degree completion with a specific focus on supervisor experiences in the context of the STEM fields, where PhD supervisors are facing unprecedented challenges amidst a shifting higher education landscape.