arXiv subjects

Alan S. Cornell

Publications and source records attributed to Alan S. Cornell.

At least 37 records · Page 2Linked to original sources

arXiv2023

Reissner-Nordström black holes in de Sitter space-time: bounds with quasinormal frequencies

Rich physics can be divined from charged black holes subjected to extremal conditions. When applied in conjunction with principles like Weak Cosmic Censorship, this naturally leads to constraints on the mass and charge of the black hole. However, more nuanced principles such as the Weak Gravity Conjecture (WGC) and the recently proposed Festina-Lente (FL) bound can provide, respectively, upper and lower bounds on elementary charged particles. In this study, we examine the quasinormal modes (QNMs) exhibited by a massive scalar test field carrying an electric charge, oscillating in the outer region of the black hole. These modes are subjected to the constraints imposed by the FL and WGC bounds. Our analysis provides insight into the behaviour of QNMs, particularly in regions that approach the extremal conditions of the black hole. Notably, in these regimes, the stability of the modes becomes precarious, particularly in the presence of a positive cosmological constant. The implications of our findings are far-reaching and significant. They extend from safeguarding the principles of cosmic censorship to addressing the structural stability of the black hole's interior. Our semi-classical analysis presents compelling evidence suggesting that Strong Cosmic Censorship may be violated for black holes that are in close proximity to extremality within the context of Reissner-Nordström-de Sitter (RNdS) geometries.

gr-qc↗

arXiv2023

Top partners and scalar dark matter -- a non-minimal reappraisal

A large set of models beyond the Standard Model of particle physics suggest that the top quark plays a special role in fundamental interactions. At the same time some of these models predict that a particle responsible for dark matter is present in the physical spectrum of the theory, and in particular cases dark matter may be specially linked to the top sector. Such a new physics configuration occurs, for instance, in composite frameworks that additionally feature vector-like quarks as mediators of the interactions of the dark matter with the Standard Model. We investigate the interplay of top-philic dark matter and the presence of several vector-like top partners. Such a non-minimal setup with several vector-like fermions is typical of composite scenarios, and we make use of an effective model to study to which extent such non-minimality modifies the collider and cosmological phenomenology of the minimal model, the latter only including one vector-like mediator of the dark matter interactions with the Standard Model.

hep-ph↗

arXiv2022

SU(5) aGUT: a minimal asymptotic grand unification model

We present a new grand unification paradigm, where gauge couplings do not need to be equal at any given scale, instead they run towards the same fixed point in the deep ultraviolet. We provide a concrete example based on SU(5) with a compactified extra space dimension. By construction, fermions are embedded in different SU(5) bulk fields, hence baryon number is conserved and proton decay is forbidden. The lightest Kaluza-Klein tier consists of stable states, providing an asymmetric Dark Matter candidate via their baryonic charges, with a mass of 2.4 TeV. The model features an interesting and predictive flavour structure.

hep-th↗

arXiv2022

Dark Matter in a Singlet Extended Inert Higgs Doublet Model

In this work, we consider an extension of the Standard Model (SM) with an inert Higgs doublet and a real scalar singlet, in order to address problems around the origin of dark matter (DM). In this model, the lightest among the CP-odd and CP-even neutral inert components plays the role of a DM candidate, where the model parameters are subject to many theoretical and experimental constraints. These constraints include vacuum stability, perturbativity, LEP negative searches, electroweak precision tests, Higgs di-photon, Higgs invisible and Higgs undetermined decays, DM relic density and DM direct detection bounds. Using these constraints, we find that the allowed parameter space for these models is quite sizeable and could be explored in upcoming collider and astrophysical searches.

hep-ph↗

arXiv2022

Neutrino specific spin-3/2 dark matter

In this paper we consider a spin-$\frac{3}{2}$ dark matter (DM) particle coupled to neutrinos as a viable candidate to produce the observed DM relic density through the thermal freeze-out mechanism. The couplings of DM to neutrinos is considered first in a most general dimension six effective field theory framework. We then consider two specific neutrino-portal models discussed in the literature. In the first model DM couples to the standard model neutrinos through mixing generated by a sterile pseudo-Dirac massive neutrino and the second model we consider is the widely studied $U(1)_{L_μ- L_τ}$ gauge symmetric model. For each of these models we explore the parameter space required to generate the observed relic density. The constraints on the parameters of these models from the existing and proposed neutrino experiments as well as from existing cosmological and astrophysical bounds are considered in the context of the relic density calculations.

hep-ph↗

arXiv2022

Using physics-informed neural networks to compute quasinormal modes

In recent years there has been an increased interest in neural networks, particularly with regard to their ability to approximate partial differential equations. In this regard, research has begun on so-called physics-informed neural networks (PINNs) which incorporate into their loss function the boundary conditions of the functions they are attempting to approximate. In this paper, we investigate the viability of obtaining the quasi-normal modes (QNMs) of non-rotating black holes in 4-dimensional space-time using PINNs, and we find that it is achievable using a standard approach that is capable of solving eigenvalue problems (dubbed the eigenvalue solver here). In comparison to the QNMs obtained via more established methods (namely, the continued fraction method and the 6th-order Wentzel, Kramer, Brillouin method) the PINN computations share the same degree of accuracy as these counterparts. In other words, our PINN approximations had percentage deviations as low as $(δω_{_{Re}}, δω_{_{Im}}) = (<0.01\%, <0.01\%)$. In terms of the time taken to compute QNMs to this accuracy, however, the PINN approach falls short, leading to our conclusion that the method is currently not to be recommended when considering overall performance.

physics.comp-ph↗

arXiv2022

Asymptotic Grand Unification: The SO(10) case

We explicitly test the asymptotic grand unification of a minimal 5-dimensional model with SO(10) gauge theory compactified on an $S^{1}/Z_{2}\times Z^{\prime}_{2}$ orbifold. We consider all matter fields as propagating in the bulk and show that the gauge couplings asymptotically run to a fixed point in the UV. However, the Yukawa couplings will typically hit a Landau pole right above the compactification scale in this class of SO(10) models.

hep-ph↗

arXiv2022

Boosted decision trees in the era of new physics: a smuon analysis case study

Machine learning algorithms are growing increasingly popular in particle physics analyses, where they are used for their ability to solve difficult classification and regression problems. While the tools are very powerful, they may often be under- or mis-utilised. In the following, we investigate the use of gradient boosting techniques as applicable to a generic particle physics problem. We use as an example a Beyond the Standard Model smuon collider analysis which applies to both current and future hadron colliders, and we compare our results to a traditional cut-and-count approach. In particular, we interrogate the use of metrics in imbalanced datasets which are characteristic of high energy physics problems, offering an alternative to the widely used area under the curve (auc) metric through a novel use of the F-score metric. We present an in-depth comparison of feature selection and investigation using a principal component analysis, Shapley values, and feature permutation methods in a way which we hope will be widely applicable to future particle physics analyses. Moreover, we show that a machine learning model can extend the 95% confidence level exclusions obtained in a traditional cut-and-count analysis, while potentially bypassing the need for complicated feature selections. Finally, we discuss the possibility of constructing a general machine learning model which is applicable to probe a two-dimensional mass plane.

hep-ph↗

arXiv2022

Asymptotic quasinormal frequencies of different spin fields in $d$-dimensional spherically-symmetric black holes

While Hod's conjecture is demonstrably restrictive, the link he observed between black hole (BH) area quantisation and the large overtone ($n$) limit of quasinormal frequencies (QNFs) motivated intense scrutiny of the regime, from which an improved understanding of asymptotic quasinormal frequencies (aQNFs) emerged. A further outcome was the development of the "monodromy technique", which exploits an anti-Stokes line analysis to extract physical solutions from the complex plane. Here, we use the monodromy technique to validate extant aQNF expressions for perturbations of integer spin, and provide new results for the aQNFs of half-integer spins within higher-dimensional Schwarzschild, Reissner-Nordström, and Schwarzschild (anti-)de Sitter BH spacetimes. Bar the Schwarzschild anti-de Sitter case, the spin-1/2 aQNFs are purely imaginary; the spin-3/2 aQNFs resemble spin-1/2 aQNFs in Schwarzschild and Schwarzschild de Sitter BHs, but match the gravitational perturbations for most others. Particularly for Schwarzschild, extremal Reissner-Nordström, and several Schwarzschild de Sitter cases, the application of $n \rightarrow \infty$ generally fixes $\mathbb{R}e \{ ω\}$ and allows for the unbounded growth of $\mathbb{I}m \{ ω\}$ in fixed quantities.

gr-qc↗

arXiv2022

Does transitioning to online classes mid-semester affect conceptual understanding?

The Force Concept Inventory (FCI) can be used as an assessment tool to measure conceptual gains in a cohort of students. The FCI uses a conceptions/"misconceptions" lens rather than a context dependent perspective, such as "knowledge-in-pieces". In this study it was given to first year students ($N=256$ students) pre- and post-mechanics lectures, at the University of Johannesburg. From these results we examine the effect of switching mid-semester from traditional classes to online classes, as imposed by the COVID-19 lockdown in South Africa. Overall results indicate no appreciable difference of gain, when bench-marked against previous studies using this assessment tool. When compared with $2019$ grades, the $2020$ semester grades do not appear to be greatly affected. Furthermore, statistical analyses also indicate a gender difference in mean gains in favour of females at the $95\%$ significance level (for paired data, $N=48$).

physics.ed-ph↗

arXiv2021

Polarising questions in the Force Concept Inventory

The Force Concept Inventory (FCI) is a well-established physics education assessment tool used to evaluate students' comprehension of elementary mechanics principles. While it can be used to analyse the effectiveness of instruction if deployed as a pre- and post-test, we utilise the FCI here as pre-test only, to extract insights into first-year students' (mis)conceptions of Newtonian mechanics as they enter university. In this preliminary study, we tested 353 students enrolled at the University of Johannesburg in 2021, across six introductory physics courses. We focus on their responses to six "polarising" questions, for which the presence of a correct and a mostly-correct answer allows for a clear demonstration of persistent misconceptions.

physics.ed-ph↗

arXiv2021

Revealing shifts from mastery of knowledge to problem solving in assessments of a tertiary physics programme

There is an increasing pressure for lecturers to work with two goals. First, they need to ensure their undergraduate students have a good grasp of the knowledge and skills of the intellectual field. In addition, they need to prepare graduates and postgraduates for careers both within and outside of academia. The problem addressed by this paper is how assessments may reveal a shift of focus from a mastery of knowledge to a work-focused orientation. This shift is examined through a case study of physics and the sub-discipline of theoretical physics as intellectual fields. The evidence is assessment tasks given to students at different points of their studies from first year to doctoral levels. By examining and analysing the assessment tasks using concepts from Legitimation Code Theory (LCT), we demonstrate how the shifts in the assessments incrementally lead students from a pure disciplinary focus to one that enables students to potentially pursue employment both within and outside of academia. In doing so, we also highlight the usefulness of LCT as a framework for evaluating the preparation of science students for diverse workplaces.

physics.ed-ph↗

arXiv2021

Quasinormal modes for integer and half-integer spins within the large angular momentum limit

While independent observations have been made regarding the behaviour of effective quasinormal mode (QNM) potentials within the large angular momentum limit, we demonstrate analytically here that a uniform expression emerges for non-rotating, higher-dimensional, and spherically-symmetric black holes (BHs) in this regime for fields of integer and half-integer spin in asymptotically flat and dS BH contexts; a second uniform expression arises for these QNM potentials in AdS BH spacetimes. We then proceed with a numerical analysis based on the multipolar expansion method recently proposed by Dolan and Ottewill to determine the behaviour of quasinormal frequencies (QNF) for varying BH parameters in the eikonal limit. We perform a complete study of Dolan and Ottewill's method for perturbations of spin $s \in \{0,1/2,1,3/2,2 \}$ in 4D Schwarzschild, Reissner-Nordstr{ö}m, and Schwarzschild de Sitter spacetimes, clarifying expressions and presenting expansions and results to higher orders $(\mathcal{O}(L^{-6}))$ than many of those presented in the literature $(\sim \mathcal{O}(L^{-2}))$. We find good agreement with known results of QNFs for low-lying modes; in the large-$\ell$ regime, our results are highly consistent with those of Konoplya's 6th-order WKB method. We confirm a universality in the trends of physical features recorded in the literature for the low-lying QNFs (that the real part grows indefinitely, the imaginary tends to a constant as $\ell \rightarrow \infty$, etc.) as we approach large values of $\ell$ within these spacetimes, and explore the consequent interplay between BH parameters and QNFs in the eikonal limit.

gr-qc↗

arXiv2021

Contact interactions and top-philic scalar dark matter

We investigate the phenomenology of a scalar top-philic dark matter candidate when adding a dimension-five contact interaction term, as motivated by possible underlying extensions of the Standard Model such as composite Higgs models. We show that the presence of contact interactions can have a major impact on the dark matter relic density as well as on its direct and indirect detection prospects, while the collider phenomenology of the model is unaffected. This underlines the complementarity of collider and cosmological constraints on dark matter models.

hep-ph↗

arXiv2021

The anomalous production of multi-lepton and its impact on the measurement of $Wh$ production at the LHC

Anomalies in multi-lepton final states at the Large Hadron Collider (LHC) have been reported in Refs.~\cite{vonBuddenbrock:2017gvy,vonBuddenbrock:2019ajh}. These can be interpreted in terms of the production of a heavy boson, $H$, decaying into a Standard Model (SM) Higgs boson, $h$, and a singlet scalar, $S$, which is treated as a SM Higgs-like boson. This process would naturally affect the measurement of the $Wh$ signal strength at the LHC, where $h$ is produced in association with leptons and di-jets. Here, $h$ would be produced with lower transverse momentum, $p_{Th}$, compared to SM processes. Corners of the phase-space are fixed according to the model parameters derived in Refs.~\cite{vonBuddenbrock:2016rmr,vonBuddenbrock:2017gvy} without additional tuning, thus nullifying potential look-else-where effects or selection biases. Provided that no stringent requirements are made on $p_{Th}$ or related observables, the signal strength of $Wh$ is $μ(Wh)=2.41 \pm 0.37$. This corresponds to a deviation from the SM of $3.8σ$. This result further strengthens the need to measure with precision the SM Higgs boson couplings in $e^+e^-$, and $e^-p$ collisions, in addition to $pp$ collisions.

hep-ph↗

arXiv2021

Minimal SU(5) Asymptotic Grand Unification

We present a minimal model of asymptotic grand unification based on an $SU(5)$ gauge theory in a compact $S^1/(\mathbb{Z}_2 \times \mathbb{Z}'_2)$ orbifold. The gauge couplings run to a unified fixed point in the UV, without supersymmetry. By construction, fermions are embedded in different $SU(5)$ bulk fields. As a consequence, baryon number is conserved, thus preventing proton decay, and the lightest Kaluza-Klein tier consists of new states that cannot decay into standard model ones. We show that the Yukawa couplings can be either in the bulk or localized, and run to an asymptotically free fixed point in the UV. The lightest massive state can play the role of Dark Matter, produced via baryogenesis, for a Kaluza-Klein mass of about $2.4$ TeV.

hep-th↗

arXiv2020

Re-visioning the postgraduate preparation of theoretical physicists: An autoethnographic account using the Specialisation dimension of Legitimation Code Theory

There is increasing pressure generally for lecturers to adapt their supervision practices of postgraduate students to better prepare postgraduate students for careers outside of academia. In this paper we examine what such pressure may mean for the supervision and preparation of theoretical physicists specifically, theoretical physics being a sub-discipline of physics usually perceived as a highly specialised niche area of scientific practice. In this exploratory study we apply the concepts of the Specialisation Dimension of Legitimation Code Theory to analyse and reveal the dominant concepts and codes, as well as the code shifts that may occur during postgraduate studies, based on an autoethnographic account of theoretical physicist identity development. The findings demonstrate an underpinning value for both knowledge and knower attributes in the journey to becoming a legitimate theoretical physicist, and the critical role played by postgraduate supervisors in facilitating the process of theoretical physicist identity development. Also highlighted are possible implications for supervisors faced with students intending to take up employment outside of academia.

physics.ed-ph↗

arXiv2020

Future lepton collider prospects for a ubiquitous composite pseudo-scalar

Composite Higgs models feature new strong dynamics leading to the description of the Higgs boson as a bound state arising from the breaking of a global (flavour) symmetry. These models generally include light states generated by the same dynamics, the detection of which may present the first observable signs of compositeness. One such state is a pseudo-scalar boson resulting from the breaking of a $U(1)$ symmetry common to most composite setups, and whose hints are expected to be visible through low-mass resonance searches at present and future hadron and lepton colliders. In this work we study the phenomenology of this pseudo-scalar field. We show that, for a light state, bottom quark loop effects dominantly impact the production cross section and considerably modify the decay pattern. Moreover, we make a case for targeted low-mass analyses at future lepton colliders, with an emphasis on high-luminosity machines aiming to operate at low centre-of-mass energies. We present a simplified outline of a search for this light pseudo-scalar at one such machine, considering electron-positron collisions at the $Z$-pole. We focus on a signature arising from the pseudo-scalar decay into a pair of hadronic taus and a production mode association with a pair of leptons of opposite electric charges, and compare cut and count methods with machine learning methods.

hep-ph↗