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Alan S. Cornell

Publications and source records attributed to Alan S. Cornell.

At least 55 records · Page 3Linked to original sources
arXiv2020

A new (original) set of Quasi-normal modes in spherically symmetric AdS black hole spacetimes

From black hole perturbation theory, quasi-normal modes (QNMs) in spherically symmetric AdS black hole spacetimes are usually studied with the Horowitz and Hubeny methods [1] by imposing the Dirichlet or vanishing energy flux boundary conditions. This method was constructed using the scalar perturbation case and box-like effective potentials, where the radial equation tends to go to infinity when the radial coordinate approaches infinity. These QNMs can be realized as a different set of solutions from those obtained by the barrier-like effective potentials. However, in some cases the existence of barrier-like effective potentials in AdS black hole spacetimes can be found. In these cases this means that we would obtain a new (original) set of QNMs by the purely ingoing and purely outgoing boundary conditions when the radial coordinate goes to the event horizon and infinity, respectively. Obtaining this set of QNMs in AdS black hole cases is the main focus of this paper.

gr-qc↗
arXiv2020

Connecting the Muon Anomalous Magnetic Moment and the Multi-lepton Anomalies at the LHC

A number of predictions were made in von Buddenbrock et al (2016 Eur. Phys. J. C 76, 10, 580) pertaining to the anomalous production of multiple leptons at the Large Hadron Collider. Discrepancies in multi-lepton final states have now become statistically compelling with the available Run~2 data. These could be connected with a heavy boson, $H$, decaying predominantly into a SM Higgs boson, $h$, and a singlet scalar, $S$, where $m_H\approx 270$\,GeV and $m_S\approx 150$\,GeV. These can be embedded into a scenario where a Two Higgs Doublet is considered with an additional singlet scalar, 2HDM+S. The long-standing discrepancy in the muon anomalous magnetic moment, $Δa_μ$, is interpreted in the context of the 2HDM+S type-II and type-X, along with additional fermionic degrees of freedom. The 2HDM+S model alone with the constraints from the LHC data does not seem to explain the $Δa_μ$ anomaly. However, adding fermions with mass of order $\mathcal{O}(100)$\,GeV can explain the discrepancy for low enough values of fermion-scalar couplings.

hep-ph↗
arXiv2019

The emergence of multi-lepton anomalies at the LHC and their compatibility with new physics at the EW scale

A recent study [1] has shown that a simplified model predicting a heavy scalar of mass 270 GeV ($H$) that decays to a Standard Model (SM) Higgs boson in association with a scalar singlet of mass 150 GeV ($S$) can accommodate several anomalous multi-lepton results in proton-proton collisions at the Large Hadron Collider (LHC). With this in mind, the goal of this article is to provide a more formal study of a wider set of LHC results pertaining to the production of multiple leptons. We find that a combination of such results lead to strong discrepancies between the data and SM Monte Carlo predictions. These discrepancies appear in corners of the phase-space where different SM processes dominate, indicating that the potential mismodeling of a single SM process is unlikely to explain them. Systematic uncertainties from the prediction of SM processes evaluated with currently available tools seem unable to explain away these discrepancies. A combination is able to constrain the simplified model's single degree of freedom $β_g^2$, related to the size of the Yukawa coupling of $H$ to the top quark, to a value of $2.92\pm 0.35$. This is in contrast to the absence of signal, where $β_g=0$. This result is discussed in the independent contexts of both potential for new physics in the existing LHC data as well as the limitations of our current understanding of the SM. That being said, QCD NNLO and EW NLO corrections in di-lepton final states are not expected to change the conclusions of this study. New results pertaining to the production of two opposite sign different flavour charged leptons with a full jet veto further confirm the presence of anomalies in similar corners of the leptonic phase-space.

hep-ph↗
arXiv2019

Constraints on a 2HDM with a singlet scalar and implications in the search for heavy bosons at the LHC

We study a two-Higgs doublet model extended with an additional singlet scalar (2HDM+S), and provide a brief introduction to the model and its parameters. Constraints are applied to the parameter space of this model in order to accommodate a number of features in the data that have been interpreted in von Buddenbrock et al (2018 J. Phys. G 45 115003) as the result of the $H\rightarrow Sh$ decay produced via gluon-gluon fusion and in association with top quarks. Implications on the phenomenology of the heavy pseudo-scalar ($A$) and charged scalar ($H^+$) are discussed. In particular, the decays $A\rightarrow ZH$ and $H^+\rightarrow W^+H$ become prominent. This leads to final states with multiple leptons and $b$-quarks. The decay $A\rightarrow ZH\rightarrow ZSh$ results in the production of a high transverse momentum $Z$ produced in association with a lepton and two $b$-quarks with little additional jet activity. These predictions are compared to the data with model's benchmark points. With the parameters obtained here the model is able to accommodate the features at the LHC reported in von Buddenbrock et al (2018 J. Phys. G 45 115003). Without varying these parameters additional excesses in the $Zb\overline{b}$ and $t\overline{t}$ invariant mass spectra, and the production of $3$ leptons plus two $b$-tagged jets can be explained assuming $m_A\approx 600$\,GeV.

hep-ph↗
arXiv2019

Master equations and Quasi-normal modes of spin-3/2 fields in Schwarzschild (A)dS black hole spacetimes

In this work we consider spin-3/2 fields in Schwarzschild (A)dS black hole spacetimes. As this spacetime is different from the Ricci-flat cases, it is necessary to modify the covariant derivative to the supercovariant derivative in order to maintain the gauge symmetry, as noted in our earlier works, where this is done here by including terms related to the cosmological constant. Together with the eigenmodes for spin-3/2 fields on an $n$-sphere, we derive the master radial equations, which have effective potentials that in general include an explicitly imaginary part and energy dependence. We found that for the asymptotically AdS cases, the explicit imaginary dependence automatically disappears, because of the negative cosmological constant. We take this case as an example and obtain the quasi-normal modes by using the Horowitz-Hubeny method [6].

gr-qc↗
arXiv2018

Towards nonsingular rotating compact object in ghost-free infinite derivative gravity

The vacuum solution of Einstein's theory of general relativity provides a rotating metric with a ring singularity, which is covered by the inner and outer horizons, and an ergo region. In this paper, we will discuss how ghost-free, quadratic curvature, Infinite Derivative Gravity (IDG) may resolve the ring singularity. In IDG the non-locality of the gravitational interaction can smear out the delta-Dirac source distribution by making the metric potential finite everywhere including at $r=0$. We show that the same feature also holds for a rotating metric. We can resolve the ring singularity such that no horizons are formed in the linear regime by smearing out a delta-source distribution on a ring. We will also show that the Kerr-metric does not solve the full non-linear equations of motion of ghost-free quadratic curvature IDG.

gr-qc↗
arXiv2018

Spin-3/2 dark matter in a simple $t$-channel model

We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple $t$-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses.

hep-ph↗
arXiv2018

Multi-lepton signatures of additional scalar bosons beyond the Standard Model at the LHC

Following a prediction made in Refs.~\cite{vonBuddenbrock:2015ema,Kumar:2016vut,vonBuddenbrock:2016rmr}, this paper focuses on multi-lepton signatures arising from two new hypothetical scalar bosons, $H$ and $S$, at the Large Hadron Collider (LHC). These two new bosons are an extension to the Standard Model (SM) and interact with the SM Higgs boson, $h$. We consider two production modes for $H$, one being gluon fusion and the other being in association with top quarks. The $H \to S h$ decay mode is considered, where leptonic final states are studied. The CP properties of $S$ are characterised by considering effective couplings derived from dimension six operators through $SWW$ vertices. The nature of the $S$ boson is considered in two separate contexts. Firstly in a simplified model, it is considered to have Higgs-like couplings. Secondly, we consider a heavy neutrino model and its interactions with the $Z, W$ and $S$ bosons. The predictions of the models are compared both to ATLAS and CMS results at $\sqrt{s} = 8$ and $13$~TeV, where appropriate. The data is interpreted using a simplified model where all the signal comes from $H \to S h$, assuming $S$ to be Higgs-like, $m_H=270$~GeV and $m_S=150$~GeV. The combined result yields gives a best fit value for the parameter $β_g$ (the strength of the Yukawa coupling of $H$ to top quarks), $β_g^2=1.38\pm 0.22$. A number of regions of the phase space are suggested to the experiments for further exploration.

hep-ph↗
arXiv2018

Quasi-normal modes of spin-3/2 fields in $D$-dimensional Reissner-Nordström black hole spacetimes using the continued fraction method

In a recent paper we calculated the field equations of spin-3/2 fields in a $D$-dimensional Reissner-Nordström black hole spacetime whilst maintaining the gauge symmetry of the Rarita-Schwinger equation. We were also able to determine the quasi-normal modes of the associated gauge invariant variables using the WKB approximation and the asymptotic iteration method (AIM). However, it was found that for higher dimension, and especially for the near extremal cases, the effective potential developed another maximum. The shape of the potential posed difficulties for the WKB approximations, as well as the AIM. As such, in this proceedings we would like to explore the connection between the AIM and the continued fraction method, and determine a possible reason for the difficulty in calculating the quasi-normal modes for spin-3/2 fields in this spacetime.

gr-qc↗
arXiv2017

Unification of gauge and Yukawa couplings

The unification of gauge and top Yukawa couplings is an attractive feature of gauge-Higgs unification models in extra-dimensions. This feature is usually considered difficult to obtain based on simple group theory analyses. We reconsider a minimal toy model including the renormalisation group running at one loop. Our results show that the gauge couplings unify asymptotically at high energies, and that this may result from the presence of an UV fixed point. The Yukawa coupling in our toy model is enhanced at low energies, showing that a genuine unification of gauge and Yukawa couplings may be achieved.

hep-ph↗
arXiv2017

The Madala hypothesis with Run 1 and 2 data at the LHC

The Madala hypothesis postulates a new heavy scalar, H, which explains several independent anomalous features seen in ATLAS and CMS data simultaneously. It has already been discussed and constrained in the literature by Run 1 results, and its underlying theory has been explored under the interpretation of a two Higgs doublet model coupled with a scalar singlet, $S$. When applying the hypothesis to Run 2 results, it can be shown that the constraints from the data are compatible with those obtained using Run 1 results.

hep-ph↗
arXiv2017

Exploring CP-even scalars of a Two Higgs-doublet model in future $e^-\,p$ colliders

In this proceeding we shall explore the potential of a future $e^- \,p$ collider to probe the CP-even scalars in a two Higgs doublet model. We consider Type-I in this study. The mass of the lighter scalar particle is considered to be the Higgs-boson, $m_h = 125$ GeV, and a heavy scalar $m_H = 270$ GeV. The centre of mass energy for the $e^-\,p$ collision is considered as in the Large Hadron Electron Collider and the Future Circular Hadron Electron Collider configurations, by fixing the proton beam energy to be $E_p = 7$ and 50 TeV, respectively, and an electron beam energy of $E_e = 60$ GeV. Production cross sections of these scalars are also shown at higher electron beam energies. Future prospects of these studies are also discussed.

hep-ph↗
arXiv2016

Minimal Spin-3/2 Dark Matter in a simple $s$-channel model

We consider a spin~-~3/2 fermionic dark matter candidate (DM) interacting with Standard Model fermions through a vector mediator in the $s$-channel. We find that for pure vector couplings almost the entire parameter space of the DM and mediator mass consistent with the observed relic density is ruled out by the direct detection observations through DM-nucleon elastic scattering cross-sections. In contrast, for pure axial-vector coupling, the most stringent constraints are obtained from mono-jet searches at the Large Hadron Collider.

hep-ph↗
arXiv2016

Probing anomalous couplings using di-Higgs production in electron-proton collisions

A proposed high energy Future Circular Hadron-Electron Collider would provide sufficient energy in a clean environment to probe di-Higgs production. Using this channel we show that the azimuthal angle correlation between the missing transverse energy and the forward jet is a very good probe for the non-standard $hhh$ and $hhWW$ couplings. We give the exclusion limits on these couplings as a function of integrated luminosity at a $95$\% C.L. using the fiducial cross sections. With appropriate error fitting methodology we find that the Higgs boson self coupling could be measured to be $g^{(1)}_{hhh} = 1.00^{+0.24(0.14)}_{-0.17(0.12)}$ of its expected Standard Model value at $\sqrt s = 3.5(5.0)$ TeV for an ultimate 10 ab$^{-1}$ of integrated luminosity.

hep-ph↗
arXiv2016

Phenomenological signatures of additional scalar bosons at the LHC

We investigate the search prospects for new scalars beyond the Standard Model (SM) at the Large Hadron Collider (LHC). In these studies two real scalars $S$ and $χ$ have been introduced in a two Higgs doublet model (2HDM), where $S$ is a portal to dark matter (DM) through its interaction with $χ$, a DM candidate and a possible source of missing transverse energy (\MET). Previous studies focused on a heavy scalar $H$ decay mode $H \to hχχ$, which was studied using an effective theory in order to explain a distortion in the Higgs ($h$) transverse momentum spectrum [16]. In this work, the effective decay is understood more deeply by including a mediator $S$, and the focus is changed to $H \to h S,~SS$ with $S \to χχ$. Phenomenological signatures of all the new scalars in the proposed 2HDM are discussed in the energy regime of the LHC, and their mass bounds have been set accordingly. Additionally, we have performed several analyses with final states including leptons and \MET, with $H \to 4 W$, $t\bar t H \to 6 W$ and $A \to ZH$ channels, in order to understand the impact these scalars have on current searches.

hep-ph↗
arXiv2016

Phenomenology of additional scalar bosons at the LHC

The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the excesses in recent Run II data suggest scenarios beyond the Standard Model (SM). We pursue a study in a minimal model which is an extension of a scalar doublet in the SM known as two-Higgs doublet model (THDM). Following earlier suggestions two real scalars $χ$ and $S$ have been introduced in the THDM where $χ$ is treated as a candidate for dark matter. $χ$ does not receive any vacuum expectation value ($vev$) in the model whereas the Higgs-like scalar $S$ acquires $vev$. This allows small mixing between the $CP$-even scalars of the THDM, $h$, $H$ and $S$. In this study the mass spectrum of new scalars is taken to be $2 m_h < m_H < 2 m_t$, $m_χ< m_h/2$, $m_h \lesssim m_S \lesssim m_H - m_h$, $m_A > 2 m_t$ and $m_H^\pm < m_A$, where $m_h$ and $m_t$ is masses of the SM Higgs and top-quark respectively, $m_H, m_A$ and $m_{H^\pm}$ are the masses of the heavy $CP$-even scalar $H$, $CP$-odd scalar $A$, and charged Higgs $H^\pm$, respectively. A partial list of potential search channels at the LHC has been provided with possible phenomenological consequences. The expected phenomenology and constraints on parameters are also discussed in a model-independent approach .

hep-ph↗
arXiv2016

The impact of additional scalar bosons at the LHC

In this study we consider an effective model by introducing two hypothetical real scalars, $H$ and $χ$ - a dark matter candidate, where the masses of these scalars are $2 m_h < m_H < 2 m_t$ and $m_χ\approx m_h/2$ with $m_h$ and $m_t$ being the Standard Model Higgs boson and top quark masses respectively. A distortion in the transverse momentum distributions of $h$ in the intermediate region of the spectrum through the processes $p p \to H \to hχχ$ could be observed in this model. An additional scalar, $S$, has been postulated to explain large $H \to hχχ$ branching ratios, assuming $m_h \lesssim m_S \lesssim m_H-m_h$ and $m_S > 2 m_χ$. Furthermore, a scenario of a two Higgs doublet model (2HDM) is introduced and a detailed proposal at the present energies of the Large Hadron Collider to study the extra CP-even ($h, H$), CP-odd ($A$) and charged ($H^\pm$) scalars has been pursued. With possible phenomenological implications, all possible spectra and decay modes for these scalars are discussed. Based on the mass spectrum of $H, A$ and $H^\pm$, the production of multi-leptons and $Z$+jets+missing-energy events are predicted. A specific, Type-II 2HDM model is discussed in detail.

hep-ph↗