A. S. Cornell

University of the Witwatersrand, Johannesburg, Gauteng, South Africa

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Publications (64)127.55 Total impact

  • Ammar. Abdalgabar, A. S. Cornell
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    ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are performed for the one-loop renormalisation group equations in six-dimensional models compactified in different possible ways to yield standard four space-time dimensions. Different possibilities for the matter fields are discussed, that is where they are in the bulk or localised to the brane. These two possibilities give rise to quite similar behaviours when studying the evolution of the Yukawa couplings and mass ratios. We find that for both scenarios, valid up to the unification scale, significant corrections are observed.
    10/2014;
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    ABSTRACT: Even if the unification and supersymmetry breaking scales are around $10^6$ to $10^{9}$ TeV, a large $A_t$ coupling may be entirely generated at low energies through RGE evolution in the 5D MSSM. Independent of the precise details of supersymmetry breaking, we take advantage of power law running in five dimensions and a compactification scale in the $10-10^3$ TeV range to show how the gluino mass may drive a large enough $A_t$ to achieve the required $125.5$ GeV Higgs mass. This also allows for sub-TeV stops, possibly observable at the LHC, and preserving GUT unification, thereby resulting in improved naturalness properties with respect to the four dimensional MSSM. The results apply also to models of "split families" in which the first and second generation matter fields are in the bulk and the third is on the boundary, which may assist in the generation of light stops whilst satisfying collider constraints on the first two generations of squarks.
    Journal of High Energy Physics 08/2014; 1407(2015):158. · 5.62 Impact Factor
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    ABSTRACT: Two compact universal extra dimensional models are an interesting class of models for different theoretical and phenomenological issues, such as the justification of having three standard model fermion families, suppression of proton decay rate, dark matter parity from relics of the 6-dimensional Lorentz symmetry, origin of masses and mixings in the standard model. However, these theories are merely effective ones, with typically a reduced range of validity in their energy scale. We explore two limiting cases of the three standard model generations all propagating in the bulk or all localised to a brane, from the point of view of renormalisation group equation evolutions for the Higgs sector and for the neutrino sector of these models. The recent experimental results of the Higgs boson from the LHC allow, in some scenarios, stronger constraints on the cut-off scale to be placed, from the requirement of the stability of the Higgs potential.
    European Physical Journal C 05/2014; 74(2014):2893. · 5.25 Impact Factor
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    ABSTRACT: The exploration of the tensor structure of the Higgs boson interaction with pairs of weak bosons may turn out to be a useful probe into physics beyond the Standard Model. Two formulations have been used here to explore the tensor structure in an electron-positron collider. This includes the study of both the processes $e^+ e^- \to \nu\bar{\nu}H$ and $e^+ e^- \to ZH$. The investigation includes a two-dimensional analysis of the polar angle and the Higgs boson momentum, such that the correlation between these variables can lead to enhanced sensitivity to new dynamics. Since the `anomalous' couplings affect the total Higgs production rate rather significantly, a scan of the total cross section can reveal the presence of higher-dimensional operators having coefficients with substantial strength. Moreover, we emphasize that some of the gauge invariant operators also affect the triple gauge boson vertices, thus leading to variation in the $W$-pair production rate.
    05/2014;
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    ABSTRACT: Even if the unification and supersymmetry breaking scales are around $10^6$ to $10^{9}$ TeV, a large $A_t$ coupling may be entirely generated at low energies through RGE evolution in the 5D MSSM. Independent of the precise details of supersymmetry breaking, we take advantage of power law running in five dimensions and a compactification scale in the $10-10^3$ TeV range to show how the gluino mass may drive a large enough $A_t$ to achieve the required $125.5$ GeV Higgs mass. This also allows for sub-TeV stops, possibly observable at the LHC, and preserving GUT unification, thereby resulting in improved naturalness properties with respect to the four dimensional MSSM. The results apply also to models of "split families" in which the first and second generation matter fields are in the bulk and the third is on the boundary, which may assist in the generation of light stops whilst satisfying collider constraints on the first two generations of squarks.
    05/2014;
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    [Show abstract] [Hide abstract]
    ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are derived for the one-loop renormalization group equations in six-dimensional models, compactified in different possible ways to yield standard four space-time dimensions. Different possibilities for the matter fields are also discussed, such as the case of bulk propagating or brane localized fields. We discuss in both cases the evolution of the Yukawa couplings, the Jarlskog parameter and the Cabibbo-Kobayashi-Maskawa matrix element, and find that for both scenarios, as we run up to the unification scale, significant renormalization group corrections are present. We also discuss the results of different observables of the five-dimensional universal extra dimension model in comparison with these six-dimensional models and the model dependence of the results.
    Physical Review D 09/2013; 88(5):056006. · 4.69 Impact Factor
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    Ammar Abdalgabar, A. S. Cornell
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    ABSTRACT: The evolution equations of the Yukawa couplings and quark mixings are derived for the one-loop renormalization group equations in the 5D Minimal Supersymmetric Standard Model on an {$S^1 / Z_2$} orbifold. Different possibilities for the matter fields are discussed such as the cases of bulk propagating or brane localised fields. We discuss in both cases the evolution of the mass ratios and the implications for the mixing angles.
    Journal of Physics Conference Series 05/2013; 455(2013):012050.
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    ABSTRACT: We review the Universal Extra-Dimensional Model compactified on a S1/Z2 orbifold, and the renormalisation group evolution of quark and lepton masses, mixing angles and phases both in the UED extension of the Standard Model and of the Minimal Supersymmetric Standard Model. We consider two typical scenarios: all matter fields propagating in the bulk, and matter fields constrained to the brane. The resulting renormalisation group evolution equations in these scenarios are compared with the existing results in the literature, together with their implications.
    Modern Physics Letters A 09/2012; 28(11). · 1.11 Impact Factor
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    Lu-Xin Liu, A. S. Cornell
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    ABSTRACT: In this paper we study the renormalization effects of the quark flavor mixings and the Higgs self-coupling in a five-dimensional model where the boson fields are propagating in the bulk while the matter fields are localized to the brane. We first explore the evolution behaviors for the Cabibbo-Kobayashi-Maskawa matrix in this scenario. Then, in light of the recent LHC bounds on the Higgs mass, we find that the Higgs self-coupling evolution has an improved vacuum stability condition, which is in contrast with that of Standard Model and the Universal Extra Dimension scenario, where the theory has a much lower ultraviolet cutoff.
    Physical review D: Particles and fields 09/2012; 86(5).
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    ABSTRACT: We consider a five-dimensional Minimal Supersymmetric Standard Model compactified on a S1/Z2 orbifold, and study the evolution of neutrino masses, mixing angles and phases for different values of tan beta and different radii of compactification. We consider the usual four dimensional Minimal Supersymmetric Standard Model limit plus two extra-dimensional scenarios: where all matter superfields can propagate in the bulk, and where they are constrained to the brane. We discuss in both cases the evolution of the mass spectrum, the implications for the mixing angles and the phases. We find that a large variation for the Dirac phase is possible, which makes models predicting maximal leptonic CP violation especially appealing.
    European Physical Journal Plus 06/2012; 128(1). · 1.30 Impact Factor
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    ABSTRACT: Leptonic decays of B-mesons are theoretically very clean probes for testing the Standard Model (SM) and possible physics beyond it. Amongst the various leptonic decays of the B-meson, the pure dileptonic decay B → ℓ+ ℓ- is very important, as this mode is helicity suppressed in the SM but can be substantially enhanced in some of the models beyond the SM, such as supersymmetric (SUSY) theories and the two Higgs doublet model (2HDM). Although the purely dileptonic decay mode is helicity suppressed in the SM its associated mode B → ℓ+ ℓ-γ does not have the same suppression, due to the presence of γ in the final state. In this paper we will also analyze the effects of enhanced Z-penguins on these two decay modes.
    International Journal of Modern Physics A 01/2012; 21(12). · 1.13 Impact Factor
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    W. A. Carlson, A. S. Cornell, B. Jordan
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    ABSTRACT: In this paper we study the fermion quasi-normal modes of a 4-dimensional rotating black-hole using the WKB(J) (to third and sixth order) and the AIM semi-analytic methods in the massless Dirac fermion sector. These semi-analytic approximations are computed in a pedagogical manner with comparisons made to the numerical values of the quasi-normal mode frequencies presented in the literature. It was found that The WKB(J) method and AIM show good agreement with direct numerical solutions for low values of the overtone number $n$ and angular quantum number l.
    01/2012;
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    ABSTRACT: In this paper we shall study the phenomenology of a doubly charged and neutral exchange black hole in an (n+3) extra-dimensional scenario, where the black hole shall be treated as a normal quantum field.
    Modern Physics Letters A 11/2011; 19(31). · 1.11 Impact Factor
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    ABSTRACT: We discuss an approach to obtaining black hole quasinormal modes (QNMs) using the asymptotic iteration method (AIM), initially developed to solve second order ordinary differential equations. We introduce the standard version of this method and present an improvement more suitable for numerical implementation. We demonstrate that the AIM can be used to find radial QNMs for Schwarzschild, Reissner-Nordstrom (RN) and Kerr black holes in a unified way. An advantage of the AIM over the standard continued fraction method (CFM) is that for differential equations with more than three regular singular points Gaussian eliminations are not required. However, the convergence of the AIM depends on the location of the radial or angular position, choosing the best such position in general remains an open problem. This review presents for the first time the spin 0, 1/2 & 2 QNMs of a Kerr black hole and the gravitational and electromagnetic QNMs of the RN black hole calculated via the AIM, and confirms results previously obtained using the CFM. We also presents some new results comparing the AIM to the WKB method. Finally we emphasize that the AIM is well suited to higher dimensional generalizations and we give an example of doubly rotating black holes.
    Advances in Mathematical Physics 11/2011; 2012. · 0.46 Impact Factor
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    ABSTRACT: We discuss a five-dimensional Minimal Supersymmetric Standard Model compactified on a $S^1/Z_2$ orbifold, looking at, in particular, the one-loop evolution equations of the Yukawa couplings for the quark sector and various flavor observables. Different possibilities for the matter fields are discussed, that is, where they are in the bulk or localised to the brane. The two possibilities give rise to quite different behaviours. By studying the implications of the evolution with the renormalisation group of the Yukawa couplings and of the flavor observables we find that, for a theory that is valid up to the unification scale, the case where fields are localised to the brane, with a large $\tan\beta$, would be more easily distinguishable from other scenarios.
    Physical review D: Particles and fields 10/2011;
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    ABSTRACT: In this paper, following the work of Chen, L\"u and Pope, we present the general metric for Kerr-(A)dS black holes with two rotations. The corresponding Klein-Gordon equation is separated explicitly, from which we develop perturbative expansions for the angular eigenvalues in powers of the rotation parameters with $D\geq 6$.
    06/2011;
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    ABSTRACT: Based on the work of Chen, Lü, and Pope, we derive expressions for the D≥6 dimensional metric for Kerr-anti-de Sitter black holes with two independent rotation parameters and all others set equal to zero: a1≠0, a2≠0, a3=a4=⋯=0. The Klein-Gordon equation is then explicitly separated on this background. For D≥6 this separation results in a radial equation coupled to two generalized spheroidal angular equations. We then develop a full numerical approach that utilizes the asymptotic iteration method to find radial quasinormal modes of doubly rotating flat Myers-Perry black holes for slow rotations. We also develop perturbative expansions for the angular quantum numbers in powers of the rotation parameters up to second order.
    Physical review D: Particles and fields 06/2011; 83(12).
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    ABSTRACT: We derive expressions for the general five-dimensional metric for Kerr-(A)dS black holes. The Klein-Gordon equation is explicitly separated and we show that the angular part of the wave equation leads to just one spheroidal wave equation, which is also that for charged five-dimensional Kerr-(A)dS black holes. We present results for the perturbative expansion of the angular eigenvalue in powers of the rotation parameters up to 6th order and compare numerically with the continued fraction method.
    Progress of Theoretical Physics 06/2011; · 2.48 Impact Factor
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    S. R. Choudhury, A. S. Cornell, J. D. Roussos
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    ABSTRACT: In this work we will study the longitudinal polarisations of both leptons in the decay process ${\bar B} \to {\bar K}_2(1430)\, \ell^+ \, \ell^-$. This process has all the features of the related and well investigated process ${\bar B} \to {\bar K}^*(890) \, \ell^+ \, \ell^-$, with theoretically comparable branching ratios. The polarised differential decay rates as well as the single and double polarisation asymmetries are worked out, where the sensitivity of these to possible right-handed couplings for the related $b \to s$ radiative decay (and other generic BSM parameters) are also investigated.
    European Physical Journal C 05/2011; 71. · 5.25 Impact Factor
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    A. S. Cornell, Lu-Xin Liu
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    ABSTRACT: In this paper we study the one-loop evolution equation of the Higgs quartic coupling $\lambda$ in the minimal Universal Extra Dimension model, and find that there are certain bounds on the extra dimension due to the singularity and vacuum stability conditions of the Higgs sector. In the range $250GeV \sim {R^{- 1}} \sim 80TeV$ of the compactification radius, we notice that for a given initial value $\lambda ({M_Z})$, there is an upper limit on ${R^{- 1}}$ for a Higgs mass of $183GeV \sim {m_H}({M_Z}) \sim 187GeV$; where any other compactification scales beyond that have been ruled out for theories where the evolution of $\lambda$ does not develop a Landau pole and become divergent in the whole range (that is, from the electroweak scale to the unification scale). Likewise, in the range of the Higgs mass $152GeV \sim {m_H}({M_Z}) \sim 157GeV$, for an initial value $\lambda ({M_Z})$, we are led to a lower limit on ${R^{- 1}}$; any other compactification scales below that will be ruled out for theories where the evolution of $\lambda$ does not become negative and destabilize the vacuum between the electroweak scale and the unification scale. For a Higgs mass in the range $157GeV < {m_H}({M_Z}) < 183GeV$, the evolution of $\lambda$ is finite and the theory is valid in the whole range (from the electroweak scale to the unification scale) for $250GeV \sim {R^{- 1}} \sim 80TeV$.
    Physical review D: Particles and fields 05/2011; 84.

Publication Stats

460 Citations
127.55 Total Impact Points

Institutions

  • 2009–2012
    • University of the Witwatersrand
      • School of Physics
      Johannesburg, Gauteng, South Africa
  • 2005–2012
    • Kyoto University
      • Yukawa Institute for Theoretical Physics
      Kioto, Kyōto, Japan
  • 2003–2011
    • Korea Institute for Advanced Study
      Sŏul, Seoul, South Korea
  • 2007–2008
    • Institut de Physique Nucléaire de Lyon
      Lyons, Rhône-Alpes, France
    • Middle East Technical University
      • Department of Physics
      Engüri, Ankara, Turkey
    • University of Lyon
      Lyons, Rhône-Alpes, France
    • Claude Bernard University Lyon 1
      • Institut de physique nucléaire de Lyon (IPNL)
      Villeurbanne, Rhone-Alpes, France
  • 2001–2008
    • University of Melbourne
      • School of Physics
      Melbourne, Victoria, Australia
  • 2004
    • University of Delhi
      • Department of Physics & Astrophysics
      Old Delhi, NCT, India