arXiv subjects

John Ellis

Publications and source records attributed to John Ellis.

At least 307 records · Page 17Linked to original sources

arXiv2007

Polarization puts a New Spin on Physics

Polarization and spin effects are useful for probing the Standard Model, in both the electroweak sector and the strong sector, where the spin decomposition of the nucleon is still a hot topic, with important new data on the net polarizations of the gluon and the strange quarks. Spin phenomena are also useful in searches for new physics, for example via measurements of the anomalous magnetic moment of the muon and searches for electric dipole moments. The cross sections for the direct detection of dark matter may also have an important spin-dependent component, related to the spin decomposition of the nucleon, that could be an important diagnostic tool. Polarization effects are also important diagnostic aids for high-energy experiments at electron-proton, proton-proton and electron-positron colliders.

hep-ph↗

arXiv2006

UHECR Particle Spectra from Crypton Decays

We calculate the spectra of ultra-high-energy cosmic rays (UHECRs) in an explicit top-down model based on the decays of metastable neutral `crypton' states in a flipped SU(5) string model. For each of the eight specific 10th-order superpotential operators that might dominate crypton decays, we calculate the spectra of both protons and photons, using a code incorporating supersymmetric evolution of the injected spectra. For all the decay operators, the total UHECR spectra are compatible with the available data. Also, the fractions of photons are compatible with all the published upper limits, but may be detectable in future experiments.

astro-ph↗

arXiv2006

Non-Perturbative Formulation of Non-Critical String Models

We apply to non-critical bosonic Liouville string models, characterized by a central-charge deficit Q, a new non-perturbative renormalization-group technique based on a functional method for controlling the quantum fluctuations. We demonstrate the existence of a renormalization-group fixed point of Liouville string theory as Q to 0, in which limit the target space-time is Minkowski and the dynamics of the Liouville field is trivial, as it neither propagates nor interacts. This calculation supports in a non-trival manner the identification of the zero mode of the Liouville field with the target time variable, up to a crucial minus sign.

hep-th↗

arXiv2006

Physics at LHC

The prospects for physics at the LHC are discussed, starting with the foretaste, preparation (and perhaps scoop) provided by the Tevatron, in particular, and then continuing through the successive phases of LHC operation. These include the start-up phase, the early physics runs, the possible search for new physics in double diffraction, the continuation to nominal LHC running, and the possible upgrade of the LHC luminosity. Emphasis is placed on the prospects for Higgs physics and the search for supersymmetry. The progress and discoveries of the LHC will set the time-scale and agenda for the major future accelerator projects that will follow it.

hep-ph↗

arXiv2006

Non-Perturbative Formulation of Time-Dependent String Solutions

We formulate here a new world-sheet renormalization-group technique for the bosonic string, which is non-perturbative in the Regge slope alpha' and based on a functional method for controlling the quantum fluctuations, whose magnitudes are scaled by the value of alpha'. Using this technique we exhibit, in addition to the well-known linear-dilaton cosmology, a new, non-perturbative time-dependent background solution. Using the reparametrization invariance of the string S-matrix, we demonstrate that this solution is conformally invariant to alpha', and we give a heuristic inductive argument that conformal invariance can be maintained to all orders in alpha'. This new time-dependent string solution may be applicable to primordial cosmology or to the exit from linear-dilaton cosmology at large times.

hep-th↗

arXiv2006

Bound-State Effects on Light-Element Abundances in Gravitino Dark Matter Scenarios

If the gravitino is the lightest supersymmetric particle and the long-lived next-to-lightest sparticle (NSP) is the stau, the charged partner of the tau lepton, it may be metastable and form bound states with several nuclei. These bound states may affect the cosmological abundances of Li6 and Li7 by enhancing nuclear rates that would otherwise be strongly suppressed. We consider the effects of these enhanced rates on the final abundances produced in Big-Bang nucleosynthesis (BBN), including injections of both electromagnetic and hadronic energy during and after BBN. We calculate the dominant two- and three-body decays of both neutralino and stau NSPs, and model the electromagnetic and hadronic decay products using the PYTHIA event generator and a cascade equation. Generically, the introduction of bound states drives light element abundances further from their observed values; however, for small regions of parameter space bound state effects can bring lithium abundances in particular in better accord with observations. We show that in regions where the stau is the NSP with a lifetime longer than 10^3-10^4 s, the abundances of Li6 and Li7 are far in excess of those allowed by observations. For shorter lifetimes of order 1000 s, we comment on the possibility in minimal supersymmetric and supergravity models that stau decays could reduce the Li7 abundance from standard BBN values while at the same time enhancing the Li6 abundance.

astro-ph↗

arXiv2006

CPT and Quantum Mechanics Tests with Kaons

In this review we first discuss the theoretical motivations for possible CPT violation and deviations from ordinary quantum-mechanical behavior of field-theoretic systems in the context of an extended class of quantum-gravity models. Then we proceed to a description of precision tests of CPT symmetry using mainly neutral kaons. We emphasize the possibly unique role of neutral meson factories in providing specific tests of models where the quantum-mechanical CPT operator is not well-defined, leading to modifications of Einstein-Podolsky-Rosen particle correlators. Finally, we present tests of CPT, T, and CP using charged kaons, and in particular K_l4 decays, which are interesting due to the high statistics attainable in experiments.

hep-ph↗

arXiv2006

What if supersymmetry breaking appears below the GUT scale?

We consider the possibility that the soft supersymmetry-breaking parameters m_{1/2} and m_0 of the MSSM are universal at some scale M_{in} below the supersymmetric grand unification scale M_{GUT}, as might occur in scenarios where either the primordial supersymmetry-breaking mechanism or its communication to the observable sector involve a dynamical scale below M_{GUT}. We analyze the (m_{1/2}, m_0) planes of such sub-GUT CMSSM models, noting the dependences of phenomenological, experimental and cosmological constraints on M_{in}. In particular, we find that the coannihilation, focus-point and rapid-annihilation funnel regions of the GUT-scale CMSSM approach and merge when M_{in} \sim 10^{12} GeV. We discuss sparticle spectra and the possible sensitivity of LHC measurements to the value of M_{in}.

hep-ph↗

arXiv2006

Higgs Phenomenology with CPsuperH

The MSSM contains CP-violating phases that may have important observable effects in Higgs physics. We review recent highlights in Higgs phenomenology obtained with the code CPsuperH, a useful tool for studies of the production, mixing and decay of a coupled system of the neutral Higgs bosons at future high energy colliders such as the LHC, ILC ($γ$LC), and a muon collider (MC). CPsuperH implements the constraints from upper limits on electric dipole moments, and may be extended to include other related low-energy observables, such as b -> s γand B -> K l l, and to compute the relic abundance of the lightest neutralino.

hep-ph↗

arXiv2006

On B_s -> mu+ mu- and Cold Dark Matter Scattering in the MSSM with Non-Universal Higgs Masses

We show that present experimental constraints on B_s -> mu+ mu- decay and the CDMS upper limit on the cold dark matter elastic scattering cross section already have significant impact on the parameter space of the minimal supersymmetric extension of the Standard Model (MSSM) with non-universal supersymmetry-breaking scalar masses for the Higgs multiplets (NUHM). The relaxation of scalar universality in the MSSM allows the possibility of a relatively light mass M_A for the pseudoscalar Higgs boson. The present upper limit on B_s -> mu+ mu- already excludes much of the scope for this possibility in the NUHM, in contrast to the constrained MSSM with universal scalar masses (CMSSM), where B_s -> mu+ mu- decay does not exclude any ranges of parameters not already excluded by b -> s γdecay. Cold dark matter scattering is also enhanced for small M_A, but the impact of present upper limit on B_s -> mu+ mu- on the NUHM parameter space is in many cases greater than that of the CDMS scattering limit, particularly at large tanb.

hep-ph↗

arXiv2005

From HERA to the LHC

Some personal comments are given on some of the exciting interfaces between the physics of HERA and the LHC. These include the quantitative understanding of perturbative QCD, the possible emergence of saturation phenomena and the Colour-Glass Condensate at small x and large Q^2, the link between forward physics and ultra-high-energy cosmic rays, and new LHC opportunities opened up by the discovery of rapidity-gap events at HERA, including the search for new physics such as Higgs bosons in double-diffraction events.

hep-ph↗

arXiv2005

On the Interpretation of B_s to mu^+ mu^- in the CMSSM

We discuss the interpretation of present and possible future experimental constraints on B_s to mu^+ mu^- decay in the context of the constrained minimal extension of the Standard Model (CMSSM) with universal scalar masses. We emphasize the importance of including theoretical and other experimental uncertainties in calculating the likelihood function, which can affect significantly the inferred 95% confidence-level limit on the CMSSM parameters. The principal uncertainties are the B_s meson decay constant, m_t and m_b. The latter induce uncertainties in the mass of the charged Higgs boson that dominates the B_s to mu^+ mu^- decay amplitude at large tan beta, reducing the CMSSM region excluded by present and possible future limits from the Fermilab Tevatron collider and the LHC.

hep-ph↗

arXiv2005

New particle physics (in French)

The first chapter treats the Standard Model of particle physics and electroweak symmetry breaking. Low-energy supersymmetry and its phenomenology at future colliders are discussed in the second chapter. Neutrino physics and lepton flavor violation appear in the third chapter. The last chapter contains an introduction to Grand-Unification, supergravity, extra dimensions, string theories and dark energy.

hep-ph↗

arXiv2005

Robust Limits on Lorentz Violation from Gamma-Ray Bursts

We constrain the possibility of a non-trivial refractive index in free space corresponding to an energy-dependent velocity of light: c(E) \simeq c_0 (1 - E/M), where M is a mass scale that might represent effect of quantum-gravitational space-time foam, using the arrival times of sharp features observed in the intensities of radiation with different energies from a large sample of gamma-ray bursters (GRBs) with known redshifts. We use wavelet techniques to identify genuine features, which we confirm in simulations with artificial added noise. Using the weighted averages of the time-lags calculated using correlated features in all the GRB light curves, we find a systematic tendency for more energetic photons to arrive earlier. However, there is a very strong correlation between the parameters characterizing an intrinsic time-lag at the source and a distance-dependent propagation effect. Moreover, the significance of the earlier arrival times is less evident for a subsample of more robust spectral structures. Allowing for intrinsic stochastic time-lags in these features, we establish a statistically robust lower limit: M > 0.9x10^{16} GeV on the scale of violation of Lorentz invariance.

astro-ph↗

arXiv2005

Resonant CP Violation in Higgs Radiation at e^+e^- Linear Collider

We study resonant CP violation in the Higgsstrahlung process e^+e^- -> H_{1,2,3} (Z -> e^+e^-, μ^+μ^-) and subsequent decays H_{1,2,3} -> b \bar{b}, τ^-τ^+, in the MSSM with Higgs-sector CP violation induced by radiative corrections. At a high-energy e^+e^- linear collider, the recoil-mass method enables one to determine the invariant mass of a fermion pair produced by Higgs decays with a precision as good as 1 GeV. Assuming an integrated luminosity of 100/fb, we show that the production lineshape of a coupled system of neutral Higgs bosons decaying into b\bar{b} quarks is sensitive to the CP-violating parameters. When the Higgs bosons decay into τ^-τ^+, two CP asymmetries can be defined using the longitudinal and transverse polarizations of the tau leptons. Taking into account the constraints from electric dipole moments, we find that these CP asymmetries can be as large as 80 %, in a tri-mixing scenario where all three neutral Higgs states of the MSSM are nearly degenerate and mix significantly.

hep-ph↗

arXiv2005

On the Higgs Mass in the CMSSM

We estimate the mass of the lightest neutral Higgs boson h in the minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking masses (CMSSM), subject to the available accelerator and astrophysical constraints. For m_t = 174.3 GeV, we find that 114 GeV < m_h < 127 GeV and a peak in the tan beta distribution simeq 55. We observe two distinct peaks in the distribution of m_h values, corresponding to two different regions of the CMSSM parameter space. Values of m_h < 119 GeV correspond to small values of the gaugino mass m_{1/2} and the soft trilinear supersymmetry-breaking parameter A_0, lying along coannihilation strips, and most of the allowed parameter sets are consistent with a supersymmetric interpretation of the possibly discrepancy in g_mu - 2. On the other hand, values of m_h > 119 GeV may correspond to much larger values of m_{1/2} and A_0, lying in rapid-annihilation funnels. The favoured ranges of m_h vary with m_t, the two peaks being more clearly separated for m_t = 178 GeV and merging for m_t = 172.7 GeV. If the g_mu - 2 constraint is imposed, the mode of the m_h distribution is quite stable, being sim 117 GeV for all the studied values of m_t.

hep-ph↗

arXiv2005

Direct Estimate of the Gluon Polarization in the Nucleon

We make a first crude direct estimate of the net gluon polarization in the proton, DeltaG, combining data on the asymmetries in high-p_T hadron production from the HERMES, SMC and COMPASS collaborations. Although these data sample a restricted range of x, they provide no hint that DeltaG is large. Fixing the normalizations of different theoretical parametrizations using the hadron asymmetry data, we find typical central values of DeltaG \sim 0.5, with uncertainties of similar magnitude. Values of DeltaG \ge 2 are disfavoured by Delta chi^2 \sim 9 to 20, depending on the parametrization used.

hep-ph↗

arXiv2005

Running of Low-Energy Neutrino Masses, Mixing Angles and CP Violation

We calculate the running of low-energy neutrino parameters from the bottom up, parameterizing the unknown seesaw parameters in terms of the dominance matrix $R$. We find significant running only if the $R$ matrix is non-trivial and the light-neutrino masses are moderately degenerate. If the light-neutrino masses are very hierarchical, the quark-lepton complementarity relation $θ_c + θ_{12} = π/4$ is quite stable, but $θ_{13,23}$ may run beyond their likely future experimental errors. The running of the oscillation phase $δ$ is enhanced by the smallness of $θ_{13}$, and jumps in the mixing angles occur in cases where the light-neutrino mass eigenstates cross.

hep-ph↗