arXiv subjects

J. Ellis

Publications and source records attributed to J. Ellis.

At least 109 records · Page 6Linked to original sources

arXiv2002

Physics Opportunities at mu+mu- Higgs Factories

We update theoretical studies of the physics opportunities presented by mu+mu- Higgs factories. Interesting measurements of the Standard Model Higgs decays into {\bar b}b, tau+tau- and WW* may be possible if the Higgs mass is less than about 160 GeV, as preferred by the precision electroweak data, the mass range being extended by varying appropriately the beam energy resolution. A suitable value of the beam energy resolution would also enable the uncertainty in the b-quark mass to be minimized, facilitating measurements of parameters in the MSSM at such a first mu+mu- Higgs factory. These measurements would be sensitive to radiative corrections to the Higgs-fermion-antifermion decay vertices, which may violate CP. Radiative corrections in the MSSM may also induce CP violation in Higgs-mass mixing, which can be probed via various asymmetries measurable using polarized mu+mu- beams. In addition, Higgs-chargino couplings may be probed at a second mu+mu- Higgs factory.

hep-ph↗

arXiv2002

Higgs-Boson Pole Masses in the MSSM with Explicit CP Violation

Extending previous results obtained in the effective-potential approach, we derive analytic expressions for the pole masses of the charged and neutral Higgs bosons in the minimal supersymmetric standard model (MSSM) with explicit CP violation. In such a minimal supersymmetric model, the CP invariance of the Higgs potential is explicitly broken by quantum effects dominated by third-generation squarks at the one-loop level and by one-loop gluino- and higgsino-mediated threshold corrections to the top- and bottom-quark Yukawa couplings at the two-loop level. Field-theoretic issues arising in the description of a two-level Higgs-boson system strongly mixed due to CP violation are addressed. Numerical results for the pole masses of the CP-violating Higgs bosons are presented, and comparisons are made with previous results obtained in the effective-potential approach.

hep-ph↗

arXiv2001

Post-LEP CMSSM Benchmarks for Supersymmetry

We introduce a set of CMSSM benchmark scenarios that take into account the constraints from LEP, Tevatron, $b \to s γ$, $g_μ- 2$ and cosmology. The benchmark points are chosen to span the range of different generic possibilities, including focus-point models, points where coannihilation effects on the relic density are important, and points with rapid relic annihilation via direct-channel Higgs poles, as well as points with smaller sparticle masses. We make initial estimates of the physics reaches of different accelerators, including the LHC, and $e^+ e^-$ colliders in the sub- and multi-TeV ranges. We stress the complementarity of hadron and lepton colliders, with the latter favoured for non-strongly-interacting particles and precision measurements.

hep-ph↗

arXiv2001

Decline and Fall of the Standard Model?

Motivations for physics beyond the Standard Model are reviewed, with particular emphasis on supersymmetry at the TeV scale. Constraints on the minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking terms (CMSSM) are discussed. These are also combined with the supersymmetric interpretation of the anomalous magnetic moment of the muon. The prospects for observing supersymmetry at accelerators are reviewed using benchmark scenarios to focus the discussion. Prospects for other experiments are discussed, including the detection of cold dark matter, mu -> e gamma and related processes, as well as proton decay.

hep-ph↗

arXiv2001

Physics with Low-Energy Muons at a Neutrino Factory Complex

The physics potential of an intense source of low-energy muons is studied. Such a source is a necessary stage towards building the neutrino factories and muon colliders which are being considered at present. The CERN Neutrino Factory could deliver muon beams with intensities 3-4 orders of magnitude higher than available now, with large freedom in the choice of the time structure. Low-energy muon physics contributes to many fields of basic research, including rare muon decays, i.e., decays that do not conserve muon number, measurements of fundamental constants, the muon anomalous magnetic moment, determination of the Lorentz structure of the weak interaction, QED tests, CPT tests, proton and nuclear charge distributions (even for short-lived isotopes), and condensed matter physics. In studying the experimental programme, we analyse the present limitations, list the requirements on the new muon beams, and describe some ideas on how to implement these beam lines in a CERN neutrino factory complex.

hep-ph↗

arXiv2001

Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity

It has recently been pointed out that generic models of quantum gravity must contend with severe phenomenological constraints imposed by gravitational Cerenkov radiation, neutrino oscillations and the cosmic microwave background radiation. We show how the non-critical Liouville-string model of quantum gravity we have proposed escapes these constraints. It gives energetic particles subluminal velocities, obviating the danger of gravitational Cerenkov radiation. The effect on neutrino propagation is naturally flavour-independent, obviating any impact on oscillation phenomenology. Deviations from the expected black-body spectrum and the effects of time delays and stochastic fluctuations in the propagation of cosmic microwave background photons are negligible, as are their effects on observable spectral lines from high-redshift astrophysical objects.

astro-ph↗

arXiv2001

Kaon physics with a high-intensity proton driver

We study opportunities for future high-precision experiments in kaon physics using a high-intensity proton driver, which could be part of the front-end of a muon storage ring complex. We discuss in particular the rare decays $K_L\toπ^0ν\barν$, $K^+\toπ^+ν\barν$, $K_L\toπ^0e^+e^-$, and lepton-flavour violating modes such as $K_L\toμe$ and $K\toπμe$. The outstanding physics potential and long-term interest of these modes is emphasized. We review status and prospects of current and planned experiments for the processes under consideration, and indicate possible improvements and strategies towards achieving the necessary higher sensitivity. Finally, we outline the machine requirements needed to perform these high-precision kaon experiments in the context of a muon storage ring facility.

hep-ph↗

arXiv2001

Proposed Post-LEP Benchmarks for Supersymmetry

We propose a new set of supersymmetric benchmark scenarios, taking into account the constraints from LEP, b to s gamma, g_mu - 2 and cosmology. We work in the context of the constrained MSSM (CMSSM) with universal soft supersymetry-breaking masses and assume that R parity is conserved. We propose benchmark points that exemplify the different generic possibilities, including focus-point models, points where coannihilation effects on the relic density are important, and points with rapid relic annihilation via direct-channel Higgs poles. We discuss the principal decays and signatures of the different classes of benchmark scenarios, and make initial estimates of the physics reaches of different accelerators, including the Tevatron collider, the LHC, and e+ e- colliders in the sub- and multi-TeV ranges. We stress the complementarity of hadron and lepton colliders, with the latter favoured for non-strongly-interacting particles and precision measurements. We mention features that could usefully be included in future versions of supersymmetric event generators.

hep-ph↗

arXiv2001

Observability of the Lightest CMSSM Higgs Boson at Hadron Colliders

We discuss the observability of the lightest neutral Higgs boson in the constrained MSSM (CMSSM), with universal soft supersymmetry-breaking parameters, at hadron colliders such as the Tevatron and the LHC. We take account of the constraints on parameter space provided by LEP, the measured rate of b to s gamma decay, the cosmological relic density Omega h^2, and the recent measurement of g_mu - 2. We normalize products of the expected CMSSM Higgs production cross sections and decay branching ratios (sigma B)_CMSSM relative to those expected for a Standard Model Higgs boson of the same mass. In the h to gamma gamma channel, we find that (sigma B)_CMSSM > 0.85 (sigma B)_SM. In the W/t tbar + h, h to b bbar channels, we find that (sigma B)_CMSSM \~ 1.05 (sigma B)_SM. We conclude that the lightest CMSSM Higgs boson should be almost as easy to see as the Standard Model Higgs boson: in particular, it should be discoverable with about 15/fb of luminosity at the Tevatron or 10/fb of luminosity at the LHC.

hep-ph↗

arXiv2001

A Neutrino Factory Manifesto

A neutrino factory is capable of answering basic questions in the physics of neutrino oscillations, which address fundamental issues in Grand Unified Theories and flavour physics. In addition, the front end of a neutrino factory offers exciting prospects using slow and stopped muons, such as the search for mu to e transitions and the muon electric dipole moment. There are also opportunities to study muonic atoms and in other areas of science. One should also keep in mind the long-term objective of building a muon collider, either for Higgs physics or at the high-energy frontier.

hep-ph↗

arXiv2001

Physics at the front-end of a neutrino factory: a quantitative appraisal

We present a quantitative appraisal of the physics potential for neutrino experiments at the front-end of a muon storage ring. We estimate the forseeable accuracy in the determination of several interesting observables, and explore the consequences of these measurements. We discuss the extraction of individual quark and antiquark densities from polarized and unpolarized deep-inelastic scattering. In particular we study the implications for the undertanding of the nucleon spin structure. We assess the determination of alpha_s from scaling violation of structure functions, and from sum rules, and the determination of sin^2(theta_W) from elastic nu-e and deep-inelastic nu-p scattering. We then consider the production of charmed hadrons, and the measurement of their absolute branching ratios. We study the polarization of Lambda baryons produced in the current and target fragmentation regions. Finally, we discuss the sensitivity to physics beyond the Standard Model.

hep-ph↗

arXiv2001

How Finely Tuned is Supersymmetric Dark Matter?

We introduce a quantification of the question in the title: the logarithmic sensitivity of the relic neutralino density Omega-hsquared to variations in input parameters such as the supersymmetric mass scales m_0, m_1/2 and A_0, tan beta and the top and bottom quark masses. In generic domains of the CMSSM parameter space with a relic density in the preferred range 0.1 < Omega-hsquared < 0.3, the sensitivities to all these parameters are moderate, so an interesting amount of supersymetric dark matter is a natural and robust prediction. Within these domains, the accuracy in measuring the CMSSM and other input parameters at the LHC may enable the relic density to be predicted quite precisely. However, in the coannihilation regions, this might require more information on the supersymetric spectrum than the LHC is able to provide. There are also exceptional domains, such as those where direct-channel pole annihilation dominates, and in the `focus-point' region, where the logarithmic sensitivity to the input parameters is greatly increased, and it would be more difficult to predict Omega-hsquared accurately.

hep-ph↗

arXiv2001

The CMSSM Parameter Space at Large tan beta

We extend previous combinations of LEP and cosmological relic density constraints on the parameter space of the constrained MSSM, with universal input supersymmetry-breaking parameters, to large tan beta. We take account of the possibility that the lightest Higgs boson might weigh about 115 GeV, but also retain the possibility that it might be heavier. We include the most recent implementation of the b to s gamma constraint at large tan beta. We refine previous relic density calculations at large tan beta by combining a careful treatment of the direct-channel Higgs poles in annihilation of pairs of neutralinos chi with a complete treatment of chi - stau coannihilation, and discuss carefully uncertainties associated with the mass of the b quark. We find that coannihilation and pole annihilations allow the CMSSM to yield an acceptable relic density at large tan beta, but it is consistent with all the constraints only if m_chi > 140 (180) GeV for mu > 0 (mu < 0) for our default choices m_b(m_b) = 4.25 GeV, m_t = 175 GeV, and A_0 = 0.

hep-ph↗

arXiv2001

Combining the Muon Anomalous Magnetic Moment with other Constraints on the CMSSM

We combine the constraint suggested by the recent BNL E821 measurement of the anomalous magnetic moment of the muon on the parameter space of the constrained MSSM (CMSSM) with those provided previously by LEP, the measured rate of b to s gamma decay and the cosmological relic density Omega-hsquared. Our treatment of Omega-hsquared includes carefully the direct-channel Higgs poles in annihilation of pairs of neutralinos chi and a complete analysis of chi - slepton coannihilation. We find excellent consistency between all the constraints for tan beta > 10 and mu > 0, for restricted ranges of the CMSSM parameters m_0 and m_1/2. All the preferred CMSSM parameter space is within reach of the LHC, but may not be accessible to the Tevatron collider, or to a first-generation e^+ e^- linear collider with centre-of-mass energy below 1.2 TeV.

hep-ph↗

arXiv2000

What if the Higgs Boson Weighs 115 GeV?

If the Higgs boson indeed weighs about 114 to 115 GeV, there must be new physics beyond the Standard Model at some scale \la 10^6 GeV. The most plausible new physics is supersymmetry, which predicts a Higgs boson weighing \la 130 GeV. In the CMSSM with R and CP conservation, the existence, production and detection of a 114 or 115 GeV Higgs boson is possible if \tanβ\ga 3. However, for the radiatively-corrected Higgs mass to be this large, sparticles should be relatively heavy: m_{1/2} \ga 250 GeV, probably not detectable at the Tevatron collider and perhaps not at a low-energy e^+ e^- linear collider. In much of the remaining CMSSM parameter space, neutralino-stau coannihilation is important for calculating the relic neutralino density, and we explore implications for the elastic neutralino-nucleon scattering cross section.

hep-ph↗

arXiv2000

Flat Directions in Flipped SU(5) I: All-Order Analysis

We present a systematic classification of field directions for the string-derived flipped SU(5) model that are D- and F-flat to all orders. Properties of the flipped SU(5) model with field values in these directions are compared to those associated with other flat directions that have been shown to be F-flat to specific finite orders in the superpotential. We discuss the phenomenological Higgs spectrum, and quark and charged-lepton mass textures.

hep-ph↗

arXiv2000

CP-Violating MSSM Higgs Bosons in the Light of LEP 2

In the MSSM, the CP parities of the neutral Higgs bosons may be mixed by radiative effects induced by explicit CP violation in the third generation of squarks. To allow for this possibility, we argue that the charged Higgs-boson mass and tan(beta) should be used to parametrize the MSSM Higgs sector. We introduce a new benchmark scenario of maximal CP violation appropriate for direct searches of CP-violating MSSM Higgs bosons. We show that the bounds established by LEP 2 on the MSSM Higgs sector may be substantially relaxed at low and intermediate values of tan(beta) in the presence of CP violation, and comment on possible Higgs boson signatures at LEP 2 within this framework.

hep-ph↗

arXiv2000

Renormalization-Group-Improved Effective Potential for the MSSM Higgs Sector with Explicit CP Violation

We perform a systematic study of the one-loop renormalization-group-improved effective potential of the minimal supersymmetric extension of the Standard Model (MSSM), including CP violation induced radiatively by soft trilinear interactions related to squarks of the third generation. We calculate the charged and neutral Higgs-boson masses and couplings, including the two-loop logarithmic corrections that arise from QCD effects, as well as those associated with the top- and bottom-quark Yukawa couplings. We also include the potentially large two-loop non-logarithmic corrections induced by one-loop threshold effects on the top- and bottom-quark Yukawa couplings, due to the decoupling of the third-generation squarks. Within this minimal CP-violating framework, the charged and neutral Higgs sectors become intimately related to one another and therefore require a unified treatment. In the limit of a large charged Higgs-boson mass, M_{H^+} >> M_Z, the lightest neutral Higgs boson resembles that in the Standard Model (SM), and CP violation occurs only in the heavy Higgs sector. Our analysis shows that sizeable radiative effects of CP violation in the Higgs sector of the MSSM may lead to significant modifications of previous studies for Higgs-boson searches at LEP2, the Tevatron and the LHC. In particular, CP violation could enable a relatively light Higgs boson to escape detection at LEP2.

hep-ph↗