arXiv subjects

John Ellis

Publications and source records attributed to John Ellis.

At least 253 records · Page 14Linked to original sources

arXiv2011

Constrained Supersymmetric Flipped SU(5) GUT Phenomenology

We explore the phenomenology of the minimal supersymmetric flipped SU(5) GUT model (CFSU(5)), whose soft supersymmetry-breaking (SSB) mass parameters are constrained to be universal at some input scale, $M_{in}$, above the GUT scale, $M_{GUT}$. We analyze the parameter space of CFSU(5) assuming that the lightest supersymmetric particle (LSP) provides the cosmological cold dark matter, paying careful attention to the matching of parameters at the GUT scale. We first display some specific examples of the evolutions of the SSB parameters that exhibit some generic features. Specifically, we note that the relationship between the masses of the lightest neutralino and the lighter stau is sensitive to $M_{in}$, as is the relationship between the neutralino mass and the masses of the heavier Higgs bosons. For these reasons, prominent features in generic $(m_{1/2}, m_0)$ planes such as coannihilation strips and rapid-annihilation funnels are also sensitive to $M_{in}$, as we illustrate for several cases with tan(beta)=10 and 55. However, these features do not necessarily disappear at large $M_{in}$, unlike the case in the minimal conventional SU(5) GUT. Our results are relatively insensitive to neutrino masses.

hep-ph↗

arXiv2011

Casting Light on Dark Matter

The prospects for detecting a candidate supersymmetric dark matter particle at the LHC are reviewed, and compared with the prospects for direct and indirect searches for astrophysical dark matter. The discussion is based on a frequentist analysis of the preferred regions of the Minimal supersymmetric extension of the Standard Model with universal soft supersymmetry breaking (the CMSSM). LHC searches may have good chances to observe supersymmetry in the near future - and so may direct searches for astrophysical dark matter particles, whereas indirect searches may require greater sensitivity, at least within the CMSSM.

hep-ph↗

arXiv2011

Neutrino Fluxes from NUHM LSP Annihilations in the Sun

We extend our previous studies of the neutrino fluxes expected from neutralino LSP annihilations inside the Sun to include variants of the minimal supersymmetric extension of the Standard Model (MSSM) with squark, slepton and gaugino masses constrained to be universal at the GUT scale, but allowing one or two non-universal supersymmetry-breaking parameters contributing to the Higgs masses (NUHM1,2). As in the constrained MSSM (CMSSM) with universal Higgs masses, there are large regions of the NUHM parameter space where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate, and there are also large regions where the capture rate is not dominated by spin-dependent LSP-proton scattering. The spectra possible in the NUHM are qualitatively similar to those in the CMSSM. We calculate neutrino-induced muon fluxes above a threshold energy of 10 GeV, appropriate for the IceCube/DeepCore detector, for points where the NUHM yields the correct cosmological relic density for representative choices of the NUHM parameters. We find that the IceCube/DeepCore detector can probe regions of the NUHM parameter space in addition to analogues of the focus-point strip and the tip of the coannihilation strip familiar from the CMSSM. These include regions with enhanced Higgsino-gaugino mixing in the LSP composition, that occurs where neutralino mass eigenstates cross over. On the other hand, rapid-annihilation funnel regions in general yield neutrino fluxes that are unobservably small.

hep-ph↗

arXiv2011

Searching for Particle Physics Beyond the Standard Model at the LHC and Elsewhere

Following a general introduction to open questions beyond the Standard Model, the prospects for addressing them in the new era opened up by the LHC are reviewed. Sample highlights are given of ways in which the LHC is already probing beyond previous experiments, including the searches for supersymmetry, quark and gluon substructure and microscopic black holes.

hep-ph↗

arXiv2011

Maximal Electric Dipole Moments of Nuclei with Enhanced Schiff Moments

The electric dipole moments (EDMs) of heavy nuclei, such as 199Hg, 225Ra and 211Rn, can be enhanced by the Schiff moments induced by the presence of nearby parity-doublet states. Working within the framework of the maximally CP-violating and minimally flavour-violating (MCPMFV) version of the MSSM, we discuss the maximal values that such EDMs might attain, given the existing experimental constraints on the Thallium, neutron and Mercury EDMs. The maximal EDM values of the heavy nuclei are obtained with the help of a differential-geometrical approach proposed recently that enables the maxima of new CP-violating observables to be calculated exactly in the linear approximation. In the case of 225Ra, we find that its EDM may be as large as 6 to 50 x 10^{-27} e.cm.

hep-ph↗

arXiv2010

On the Interpretation of Gravitational Corrections to Gauge Couplings

Several recent papers discuss gravitational corrections to gauge couplings that depend quadratically on the energy. In the framework of the background-field approach, these correspond in general to adding to the effective action terms quadratic in the field strength but with higher-order space-time derivatives. We observe that such terms can be removed by appropriate local field redefinitions, and do not contribute to physical scattering-matrix elements. We illustrate this observation in the context of open string theory, where the effective action includes, among other terms, the well-known Born-Infeld form of non-linear electrodynamics. We conclude that the quadratically energy-dependent gravitational corrections are \emph{not} physical in the sense of contributing to the running of a physically-measurable gauge coupling, or of unifying couplings as in string theory.

hep-th↗

arXiv2010

New Light on Dark Matter from the LHC

The prospects for detecting a candidate supersymmetric dark matter particle at the LHC are reviewed, and compared with the prospects for direct and indirect searches for astrophysical dark matter, on the basis of a frequentist analysis of the preferred regions of the Minimal supersymmetric extension of the Standard Model with universal soft supersymmetry breaking (the CMSSM) and a model with equal but non-universal supersymmetry-breaking contributions to the Higgs masses (the NUHM1). LHC searches may have good chances to observe supersymmetry in the near future - and so may direct searches for astrophysical dark matter particles.

hep-ph↗

arXiv2010

Beyond the Standard Model for Montaneros

These notes cover (i) electroweak symmetry breaking in the Standard Model (SM) and the Higgs boson, (ii) alternatives to the SM Higgs boson including an introduction to composite Higgs models and Higgsless models that invoke extra dimensions, (iii) the theory and phenomenology of supersymmetry, and (iv) various further beyond topics, including Grand Unification, proton decay and neutrino masses, supergravity, superstrings and extra dimensions.

hep-ph↗

arXiv2010

Note on a Differential-Geometrical Construction of Optimal Directions in Linearly-Constrained Systems

This note presents an analytic construction of the optimal unit-norm direction hat(x) = x/|x| that maximizes or minimizes the objective linear expression, B . hat(x), subject to a system of linear constraints of the form [A] . x = 0, where x is an unknown n-dimensional real vector to be determined up to an overall normalization constant, 0 is an m-dimensional null vector, and the n-dimensional real vector B and the m\times n-dimensional real matrix [A] (with 0 =< m < n) are given. The analytic solution to this problem can be expressed in terms of a combination of double wedge and Hodge-star products of differential forms.

math.OC↗

arXiv2010

A Geometric Approach to CP Violation: Applications to the MCPMFV SUSY Model

We analyze the constraints imposed by experimental upper limits on electric dipole moments (EDMs) within the Maximally CP- and Minimally Flavour-Violating (MCPMFV) version of the MSSM. Since the MCPMFV scenario has 6 non-standard CP-violating phases, in addition to the CP-odd QCD vacuum phase θ_QCD, cancellations may occur among the CP-violating contributions to the three measured EDMs, those of the Thallium, neutron and Mercury, leaving open the possibility of relatively large values of the other CP-violating observables. We develop a novel geometric method that uses the small-phase approximation as a starting point, takes the existing EDM constraints into account, and enables us to find maximal values of other CP-violating observables, such as the EDMs of the Deuteron and muon, the CP-violating asymmetry in b --> s γdecay, and the B_s mixing phase. We apply this geometric method to provide upper limits on these observables within specific benchmark supersymmetric scenarios, including extensions that allow for a non-zero θ_QCD.

hep-ph↗

arXiv2010

Nuclear Reaction Uncertainties, Massive Gravitino Decays and the Cosmological Lithium Problem

We consider the effects of uncertainties in nuclear reaction rates on the cosmological constraints on the decays of unstable particles during or after Big-Bang nucleosynthesis (BBN). We identify the nuclear reactions due to non-thermal hadrons that are the most important in perturbing standard BBN, then quantify the uncertainties in these reactions and in the resulting light-element abundances. These results also indicate the key nuclear processes for which improved cross section data would allow different light-element abundances to be determined more accurately, thereby making possible more precise probes of BBN and evaluations of the cosmological constraints on unstable particles. Applying this analysis to models with unstable gravitinos decaying into neutralinos, we calculate the likelihood function for the light-element abundances measured currently, taking into account the current experimental errors in the determinations of the relevant nuclear reaction rates. We find a region of the gravitino mass and abundance in which the abundances of deuterium, He4 and Li7 may be fit with chi^2 = 5.5, compared with chi^2 = 31.7 if the effects of gravitino decays are unimportant. The best-fit solution is improved to chi^2 ~ 2.0 when the lithium abundance is taken from globular cluster data. Some such re-evaluation of the observed light-element abundances and/or nuclear reaction rates would be needed if this region of gravitino parameters is to provide a complete solution to the cosmological Li7 problem.

astro-ph.CO↗

arXiv2010

What if Supersymmetry Breaking Unifies beyond the GUT Scale?

We study models in which soft supersymmetry-breaking parameters of the MSSM become universal at some unification scale, $M_{in}$, above the GUT scale, $\mgut$. We assume that the scalar masses and gaugino masses have common values, $m_0$ and $m_{1/2}$ respectively, at $M_{in}$. We use the renormalization-group equations of the minimal supersymmetric SU(5) GUT to evaluate their evolutions down to $\mgut$, studying their dependences on the unknown parameters of the SU(5) superpotential. After displaying some generic examples of the evolutions of the soft supersymmetry-breaking parameters, we discuss the effects on physical sparticle masses in some specific examples. We note, for example, that near-degeneracy between the lightest neutralino and the lighter stau is progressively disfavoured as $M_{in}$ increases. This has the consequence, as we show in $(m_{1/2}, m_0)$ planes for several different values of $\tan β$, that the stau coannihilation region shrinks as $M_{in}$ increases, and we delineate the regions of the $(M_{in}, \tan β)$ plane where it is absent altogether. Moreover, as $M_{in}$ increases, the focus-point region recedes to larger values of $m_0$ for any fixed $\tan β$ and $m_{1/2}$. We conclude that the regions of the $(m_{1/2}, m_0)$ plane that are commonly favoured in phenomenological analyses tend to disappear at large $M_{in}$.

hep-ph↗

arXiv2010

Do Three Dimensions tell us Anything about a Theory of Everything?

It has been conjectured that four-dimensional N=8 supergravity may provide a suitable framework for a `Theory of Everything', if its composite SU(8) gauge fields become dynamical. We point out that supersymmetric three-dimensional coset field theories motivated by lattice models provide toy laboratories for aspects of this conjecture. They feature dynamical composite supermultiplets made of constituent holons and spinons. We show how these models may be extended to include N=1 and N=2 supersymmetry, enabling dynamical conjectures to be verified more rigorously. We point out some special features of these three-dimensional models, and mention open questions about their relevance to the dynamics of N=8 supergravity.

hep-th↗

arXiv2010

Resurrecting No-Scale Supergravity Phenomenology

In the context of phenomenological models in which the soft supersymmetry-breaking parameters of the MSSM become universal at some unification scale, M_{in}, above the GUT scale, \mgut, it is possible that all the scalar mass parameters m_0, the trilinear couplings A_0 and the bilinear Higgs coupling B_0 vanish simultaneously, as in no-scale supergravity. Using these no-scale inputs in a renormalization-group analysis of the minimal supersymmetric SU(5) GUT model, we pay careful attention to the matching of parameters at the GUT scale. We delineate the region of M_{in}, m_{1/2} and \tan βwhere the resurrection of no-scale supergravity is possible, taking due account of the relevant phenomenological constraints such as electroweak symmetry breaking, m_h, b \to s γ, the neutralino cold dark matter density \ohsq and g_μ- 2. No-scale supergravity survives in an L-shaped strip of parameter space, with one side having with one side having m_{1/2} \gappeq 200 {\rm GeV}, the second (orthogonal) side having M_{in} \gappeq 5 \times 10^{16} GeV. Depending on the relative signs and magnitudes of the GUT superpotential couplings, these may be connected to form a triangle whose third side is a hypotenuse at larger M_{in}, m_{1/2} and \tan β, whose presence and location depend on the GUT superpotential parameters. We compare the prospects for detecting sparticles at the LHC in no-scale supergravity with those in the CMSSM and the NUHM.

hep-ph↗

arXiv2010

Comments on Ultra-High-Energy Photons and D-Foam models

We revisit the constraints that the non-observation of ultra-high-energy photons due to the GZK cutoff can impose on models of Lorentz violation in photon propagation, following recent work by Maccione, Liberati and Sigl [arXiv:1003.5468] that carries further an earlier analysis by the present authors (Phys. Rev. D 63,12402 (2001), [hep-th/0012216]). We argue that the GZK cutoff constraint is naturally evaded in the D-brane model of space-time foam presented recently by the present authors (Phys. Lett. B 665, 412 (2008) [arXiv:0804.3566]), in which Lorentz-violating effects on photon propagation are independent of possible effects during interactions. We also note a novel absorption mechanism that could provide a GZK-like cutoff for photons in low-scale string models.

astro-ph.HE↗

arXiv2010

Prospects for New Physics at the LHC

High-energy collisions at the LHC are now starting. The new physics agenda of the LHC is reviewed, with emphasis on the hunt for the Higgs boson (or whatever replaces it) and supersymmetry. In particular, the prospects for discovering new physics in the 2010-2011 run are discussed.

hep-ph↗

arXiv2010

Neutrino Fluxes from CMSSM LSP Annihilations in the Sun

We evaluate the neutrino fluxes to be expected from neutralino LSP annihilations inside the Sun, within the minimal supersymmetric extension of the Standard Model with supersymmetry-breaking scalar and gaugino masses constrained to be universal at the GUT scale (the CMSSM). We find that there are large regions of typical CMSSM $(m_{1/2}, m_0)$ planes where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate. We show that neutrino fluxes are dependent on the solar model at the 20% level, and adopt the AGSS09 model of Serenelli et al. for our detailed studies. We find that there are large regions of the CMSSM $(m_{1/2}, m_0)$ planes where the capture rate is not dominated by spin-dependent LSP-proton scattering, e.g., at large $m_{1/2}$ along the CMSSM coannihilation strip. We calculate neutrino fluxes above various threshold energies for points along the coannihilation/rapid-annihilation and focus-point strips where the CMSSM yields the correct cosmological relic density for tan(beta) = 10 and 55 for $μ$ > 0, exploring their sensitivities to uncertainties in the spin-dependent and -independent scattering matrix elements. We also present detailed neutrino spectra for four benchmark models that illustrate generic possibilities within the CMSSM. Scanning the cosmologically-favored parts of the parameter space of the CMSSM, we find that the IceCube/DeepCore detector can probe at best only parts of this parameter space, notably the focus-point region and possibly also at the low-mass tip of the coannihilation strip.

hep-ph↗

arXiv2010

Supersymmetric Dark Matter Candidates

After reviewing the theoretical, phenomenological and experimental motivations for supersymmetric extensions of the Standard Model, we recall that supersymmetric relics from the Big Bang are expected in models that conserve R parity. We then discuss possible supersymmetric dark matter candidates, focusing on the lightest neutralino and the gravitino. In the latter case, the next-to-lightest supersymmetric particle is expected to be long-lived, and possible candidates include spartners of the tau lepton, top quark and neutrino. We then discuss the roles of the renormalization-group equations and electroweak symmetry breaking in delimiting the supersymmetric parameter space. We discuss in particular the constrained minimal extension of the Standard Model (CMSSM), in which the supersymmetry-breaking parameters are assumed to be universal at the grand unification scale, presenting predictions from a frequentist analysis of its parameter space. We also discuss astrophysical and cosmological constraints on gravitino dark matter models, as well as the parameter space of minimal supergravity (mSUGRA) models in which there are extra relations between the trilinear and bilinear supersymmetry-breaking parameters, and between the gravitino and scalar masses. Finally, we discuss models with non-universal supersymmetry-breaking contributions to Higgs masses, and models in which the supersymmetry-breaking parameters are universal at some scale below that of grand unification. http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684

astro-ph.CO↗