arXiv subjects

John Ellis

Publications and source records attributed to John Ellis.

At least 91 records · Page 5Linked to original sources

arXiv2021

A Minimal Supersymmetric SU(5) Missing-Partner Model

We explore a missing-partner model based on the minimal SU(5) gauge group with $\bf{75}$, $\bf{50}$ and $\bf{\overline{50}}$ Higgs representations, assuming a super-GUT CMSSM scenario in which soft supersymmetry-breaking parameters are universal at some high scale $M_{\rm in}$ above the GUT scale $M_{\rm GUT}$. We identify regions of parameter space that are consistent with the cosmological dark matter density, the measured Higgs mass and the experimental lower limit on $τ(p \to K^+ ν)$. These constraints can be satisfied simultaneously along stop coannihilation strips in the super-GUT CMSSM with $\tan β\sim 3.5 - 5$ where the input gaugino mass $m_{1/2} \sim 15 - 25$~TeV, corresponding after strong renormalization by the large GUT Higgs representations between $M_{\rm in}$ and $M_{\rm GUT}$ to $m_{\rm LSP}, m_{\tilde t_1} \sim 2.5 - 5$~TeV and $m_{\tilde g} \sim 13 - 20$~TeV, with the light-flavor squarks significantly heavier. We find that $τ(p \to K^+ ν) \lesssim 3 \times 10^{34}$~yrs throughout the allowed range of parameter space, within the range of the next generation of searches with the JUNO, DUNE and Hyper-Kamiokande experiments.

hep-ph↗

arXiv2021

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

The interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation[1,2]. While the structural and dynamical properties of water at interfaces differ strongly from those in the bulk, major gaps in our knowledge at the molecular level still prevent us from understanding these ubiquitous chemical processes. Information concerning the microscopic motion of water comes mostly from computational simulation[3,4] but the dynamics of molecules, on the atomic scale, is largely unexplored by experiment. Here we present experimental results combined with ab initio calculations to provide a detailed insight into the behaviour of water monomers on a graphene surface. We show that motion occurs by activated hopping on the graphene lattice. The dynamics of water diffusion displays remarkably strong signatures of cooperative behaviour due to repulsive forces between the monomers. The repulsive forces enhance the monomer lifetime ($t_m \approx 3$ s at $T_S = 125$ K) in a $\textit{free-gas}$ phase that precedes the nucleation of ice islands and, in turn, provides the opportunity for our experiments to be performed. Our results give a unique molecular perspective of barriers to ice nucleation on material surfaces, providing new routes to understand and potentially control the more general process of ice formation.

cond-mat.mtrl-sci↗

arXiv2021

Non-Oscillatory No-Scale Inflation

We propose a non-oscillatory no-scale supergravity model of inflation (NO-NO inflation) in which the inflaton does not oscillate at the end of the inflationary era. Instead, the Universe is then dominated by the inflaton kinetic energy density (kination). During the transition from inflation to kination, the Universe preheats instantly through a coupling to Higgs-like fields. These rapidly annihilate and scatter into ultra-relativistic matter particles, which subsequently dominate the energy density, and reheating occurs at a temperature far above that of Big Bang Nucleosynthesis. After the electroweak transition, the inflaton enters a tracking phase as in some models of quintessential inflation. The model predictions for cosmic microwave background observables are consistent with Planck 2018 data, and the density of gravitational waves is below the upper bound from Big Bang Nucleosynthesis. We also find that the density of supersymmetric cold dark matter produced by gravitino decay is consistent with Planck 2018 data over the expected range of supersymmetric particle masses.

hep-ph↗

arXiv2021

Cosmic String Interpretation of NANOGrav Pulsar Timing Data

Pulsar timing data used to provide upper limits on a possible stochastic gravitational wave background (SGWB). However, the NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension $Gμ\in (4 \times 10^{-11}, 10^{-10}) $ at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers. The SGWB produced by cosmic strings with such values of $Gμ$ would be beyond the reach of LIGO, but could be measured by other planned and proposed detectors such as SKA, LISA, TianQin, AION-1km, AEDGE, Einstein Telescope and Cosmic Explorer.

astro-ph.CO↗

arXiv2021

Discrete spacetime symmetries and particle mixing in non-Hermitian scalar quantum field theories

We discuss second quantization, discrete symmetry transformations and inner products in free non-Hermitian scalar quantum field theories with PT symmetry, focusing on a prototype model of two complex scalar fields with anti-Hermitian mass mixing. Whereas the definition of the inner product is unique for theories described by Hermitian Hamiltonians, its formulation is not unique for non-Hermitian Hamiltonians. Energy eigenstates are not orthogonal with respect to the conventional Dirac inner product, so we must consider additional discrete transformations to define a positive-definite norm. We clarify the relationship between canonical-conjugate operators and introduce the additional discrete symmetry C', previously introduced for quantum-mechanical systems, and show that the C'PT inner product does yield a positive-definite norm, and hence is appropriate for defining the Fock space in non-Hermitian models with PT symmetry in terms of energy eigenstates. We also discuss similarity transformations between PT-symmetric non-Hermitian scalar quantum field theories and Hermitian theories, showing that they would require modification in the presence of interactions. As an illustration of our discussion, we compare particle mixing in a Hermitian theory and in the corresponding non-Hermitian model with PT symmetry, showing how the latter maintains unitarity and exhibits mixing between scalar and pseudoscalar bosons.

hep-th↗

arXiv2020

Probing New Physics in Dimension-8 Neutral Gauge Couplings at $e^+e^-$ Colliders

Neutral triple gauge couplings (nTGCs) are absent in the standard model effective theory up to dimension-6 operators, but could arise from dimension-8 effective operators. In this work, we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet. We show that the pure gauge operators generate both $ZγZ^*$ and $Zγγ^*$ vertices with rapid energy dependence $\propto E^5$, which can be probed sensitively via the reaction $e^+e^- \to Zγ$. We demonstrate that measuring the nTGCs via the reaction $e^+e^- \to Zγ$ followed by $Z \to q\bar{q}$ decays can probe the new physics scales of dimension-8 pure gauge operators up to the range $(1-5)$TeV at the CEPC, FCC-ee and ILC colliders with $\sqrt{s}=(0.25-1)$TeV, and up to the range $(10-16)$TeV at CLIC with $\sqrt{s}=(3-5)$TeV, assuming in each case an integrated luminosity of 5/ab. We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the $e^+e^-Zγ$ vertex.

hep-ph↗

arXiv2020

Low-Energy Probes of No-Scale SU(5) Super-GUTs

We explore the possible values of the $μ\to e γ$ branching ratio, $\text{BR}(μ\rightarrow eγ)$, and the electron dipole moment (eEDM), $d_e$, in no-scale SU(5) super-GUT models with the boundary conditions that soft supersymmetry-breaking matter scalar masses vanish at some high input scale, $M_{\rm in}$, above the GUT scale, $M_{\rm GUT}$. We take into account the constraints from the cosmological cold dark matter density, $Ω_{CDM} h^2$, the Higgs mass, $M_h$, and the experimental lower limit on the lifetime for $p \to K^+ \bar ν$, the dominant proton decay mode in these super-GUT models. Reconciling this limit with $Ω_{CDM} h^2$ and $M_h$ requires the Higgs field responsible for the charge-2/3 quark masses to be twisted, and possibly also that responsible for the charge-1/3 and charged-lepton masses, with model-dependent soft supersymmetry-breaking masses. We consider six possible models for the super-GUT initial conditions, and two possible choices for quark flavor mixing, contrasting their predictions for proton decay with versions of the models in which mixing effects are neglected. We find that $τ\left(p\rightarrow K^+ \barν\right)$ may be accessible to the upcoming Hyper-Kamiokande experiment, whereas all the models predict $\text{BR}(μ\rightarrow eγ)$ and $d_e$ below the current and prospective future experimental sensitivities or both flavor choices, when the dark matter density, Higgs mass and current proton decay constraints are taken into account. However, there are limited regions with one of the flavor choices in two of the models where $μ\to e$ conversion on a heavy nucleus may be observable in the future. Our results indicate that there is no supersymmetric flavor problem in the class of no-scale models we consider.

hep-ph↗

arXiv2020

Inter-adsorbate forces and coherent scattering in helium spin-echo experiments

In studies of dynamical systems, helium atoms scatter coherently from an ensemble of adsorbates as they diffuse on the surface. The results give information on the co-operative behaviour of interacting adsorbates and thus include the effects of both adsorbate-substrate and adsorbate-adsorbate interactions. Here, we discuss a method to disentangle the effects of interactions between adsorbates from those with the substrate. The result gives an approximation to observations that would be obtained if the scattering was incoherent. Information from the experiment can therefore be used to distinguish more clearly between long-range inter-adsorbate forces and the short range effects arising from the local lattice potential and associated thermal excitations. The method is discussed in the context of a system with strong inter-adsorbate interactions, sodium atoms diffusing on a copper (111) surface.

cond-mat.mtrl-sci↗

arXiv2020

Detecting circular polarisation in the stochastic gravitational-wave background from a first-order cosmological phase transition

We discuss the observability of circular polarisation of the stochastic gravitational-wave background (SGWB) generated by helical turbulence following a first-order cosmological phase transition, using a model that incorporates the effects of both direct and inverse energy cascades. We explore the strength of the gravitational-wave signal and the dependence of its polarisation on the helicity fraction, $ζ_*$, the strength of the transition, $α$, the bubble size, $R_*$, and the temperature, $T_*$, at which the transition finishes. We calculate the prospective signal-to-noise ratios of the SGWB strength and polarisation signals in the LISA experiment, exploring the parameter space in a way that is minimally sensitive to the underlying particle physics model. We find that discovery of SGWB polarisation is generally more challenging than measuring the total SGWB signal, but would be possible for appropriately strong transitions with large bubble sizes and a substantial polarisation fraction.

astro-ph.CO↗

arXiv2020

Building Models of Inflation in No-Scale Supergravity

After reviewing the motivations for cosmological inflation formulated in the formalism of supersymmetry, we argue that the appropriate framework is that of no-scale supergravity. We then show how to construct within this framework inflationary models whose predictions for the tilt in the spectrum of scalar perturbations, $n_s$, and the ratio, $r$, of tensor and scalar perturbations coincide with those of the $R + R^2$ model of inflation proposed by Starobinsky. A more detailed study of no-scale supergravity reveals a structure that is closely related to that of $R^2$ modifications of the minimal Einstein-Hilbert action for general relativity, opening avenues for constructing no-scale de Sitter and anti-de Sitter models by combining pairs of Minkowski models, as well as generalizations of the original no-scale Starobinsky models of inflation. We then discuss the phenomenology of no-scale models of inflation, including inflaton decay and reheating, and then the construction of explicit scenarios based on SU(5), SO(10) and string-motivated flipped SU(5)$\times$U(1) GUT models. The latter provides a possible model of almost everything below the Planck scale, including neutrino masses and oscillations, the cosmological baryon asymmetry and cold dark matter, as well as $n_s$ and $r$.

hep-ph↗

arXiv2020

Supernova Triggers for End-Devonian Extinctions

The Late Devonian was a protracted period of low speciation resulting in biodiversity decline, culminating in extinction events near the Devonian-Carboniferous boundary. Recent evidence indicates that the final extinction event may have coincided with a dramatic drop in stratospheric ozone, possibly due to a global temperature rise. Here we study an alternative possible cause for the postulated ozone drop: a nearby supernova explosion that could inflict damage by accelerating cosmic rays that can deliver ionizing radiation for up to $\sim 100$ kyr. We therefore propose that the end-Devonian extinctions were triggered by supernova explosions at $\sim 20$ pc, somewhat beyond the "kill distance" that would have precipitated a full mass extinction. Such nearby supernovae are likely due to core-collapses of massive stars; these are concentrated in the thin Galactic disk where the Sun resides. Detecting either of the long-lived radioisotopes Sm-146 or Pu-244 in one or more end-Devonian extinction strata would confirm a supernova origin, point to the core-collapse explosion of a massive star, and probe supernova nucleosythesis. Other possible tests of the supernova hypothesis are discussed.

astro-ph.HE↗

arXiv2020

Phenomenology and Cosmology of No-Scale Attractor Models of Inflation

We have recently proposed attractor models for modulus fixing, inflation, supersymmetry breaking and dark energy based on no-scale supergravity. In this paper we develop phenomenological and cosmological aspects of these no-scale attractor models that underpin their physical applications. We consider models in which inflation is driven by a modulus field ($T$-type) with supersymmetry broken by a Polonyi field, or a matter field ($ϕ$-type) with supersymmetry broken by the modulus field. We derive the possible patterns of soft supersymmetry-breaking terms, which depend in $T$-type models whether the Polonyi and/or matter fields are twisted or not, and in $ϕ$-type models on whether the inflaton and/or other matter fields are twisted or not. In $ϕ$-type models, we are able to directly relate the scale of supersymmetry breaking to the inflaton mass. We also discuss cosmological constraints from entropy considerations and the density of dark matter on the mechanism for stabilizing the modulus field via higher-order terms in the no-scale Kähler potential.

hep-ph↗

arXiv2020

Updated predictions for gravitational waves produced in a strongly supercooled phase transition

We update predictions for the gravitational wave (GW) signal from a strongly supercooled phase transition in an illustrative classically conformal U(1)$_{B-L}$ model. We implement $\propto γ^2$ scaling of the friction on the bubble wall and update the estimates for the efficiency factors for GW production from bubble collisions and plasma-related sources. We take into account the fact that a small decay rate of the symmetry-breaking field may lead to brief matter-dominated era after the transition, as the field oscillates around its minimum before decaying. We find that a strong bubble collision signal occurs in a significant part of the parameter space, and that the modified redshift of the modes that re-enter the horizon during the matter-dominated period generates a characteristic tilted `plateau' in the spectrum. The GW spectrum in this model would be detectable in the low-frequency range, e.g., by LISA, and in the mid-frequency range, e.g., by AION/MAGIS and AEDGE, and in the high-frequency range by LIGO and ET. The peak frequency of the signal is limited from below by collider constraints on the mass of the U(1)$_{B-L}$ gauge boson, while at high frequencies the slow decay of the scalar field and the resulting matter-dominated era diminishes the GW signal.

astro-ph.CO↗

arXiv2020

Supercritical String Cosmology drains the Swampland

The First and Second Swampland Conjectures (FSC & SSC) are substantially modified in non-critical string cosmology, in which cosmic time is identified with the time-like Liouville mode of the supercritical string. In this scenario the Friedmann equation receives additional contributions due to the non-criticality of the string. These are potentially important when one seeks to apply the Bousso bound for the entropy of states that may become light as the dilaton takes on trans-Planckian values, as in a de Sitter phase, and restore consistency with the FSC and in at least some cases also the SSC. The weak gravity conjecture (WGC) for scalar potentials is saturated in the supercritical string scenarios discussed in this work, but only if one uses the dilaton as appears in the string effective action, with a kinetic term that is not canonically normalised. In the case of a non-critical Starobinsky potential, the WGC is satisfied by both the canonically-normalised dilaton and the dilaton used in the string effective action.

hep-th↗

arXiv2020

Probes of Gravitational Waves with Atom Interferometers

Atom interferometers (AIs) on earth and in space offer good capabilities for measuring gravitational waves (GWs) in the mid-frequency deciHz band, complementing the sensitivities of the LIGO/Virgo and LISA experiments and enabling probes of possible modifications of the general relativity predictions for GW propagation. We illustrate these capabilities using the projected sensitivities of the AION (terrestrial) and AEDGE (space-based) AI projects, showing that AION could improve the present LIGO/Virgo direct limit on the graviton mass by a factor $\sim 40$ to $\simeq 10^{-24}\,$eV, and AEDGE could improve the limit by another order of magnitude. AION and AEDGE will also have greater sensitivity than LIGO to some scenarios for Lorentz violation.

gr-qc↗

arXiv2020

PT-Symmetric Non-Hermitian Quantum Field Theories with Supersymmetry

We formulate supersymmetric non-Hermitian quantum field theories with PT symmetry, starting with free chiral boson/fermion models and then including trilinear superpotential interactions. We consider models with both Dirac and Majorana fermions, analyzing them in terms of superfields and at the component level. We also discuss the relation between the equations of motion, the (non-)invariance of the Lagrangian and the (non-)conservation of the supercurrents in the two models. We exhibit a similarity transformation that maps the free-field supersymmetric PT-symmetric Dirac model to a supersymmetric Hermitian theory, but there is, in general, no corresponding similarity transformation for the Majorana model. In this model, we find generically a mass splitting between bosons and fermions, even though its construction is explicitly supersymmetric, offering a novel non-Hermitian mechanism for soft supersymmetry breaking.

hep-th↗

arXiv2020

Correction to: A Practical, Provably Linear Time, In-place and Stable Merge Algorithm via the Perfect Shuffle

We correct a paper previously submitted to CoRR. That paper claimed that the algorithm there described was provably of linear time complexity in the average case. The alleged proof of that statement contained an error, being based on an invalid assumption, and is invalid. In this paper we present both experimental and analytical evidence that the time complexity is of order $N^2$ in the average case, where $N$ is the total length of the merged sequences.

cs.DS↗

arXiv2020

Probing the Scale of New Physics in the $ZZγ$ Coupling at $e^+e^-$ Colliders

The $ZZγ$ triple neutral gauge couplings are absent in the Standard Model (SM) at the tree level. They receive no contributions from dimension-6 effective operators, but can arise from effective operators of dimension-8. We study the scale of new physics associated with such dimension-8 operators that can be probed by measuring the reaction $e^+e^-\to Zγ$, followed by $Z \to \ell\bar{\ell},ν\barν$ decays, at future $e^+e^-$ colliders including the ILC, CEPC, FCC-ee and CLIC. We demonstrate how angular distributions of the final state mono-photon and leptons can play a key role in suppressing SM backgrounds. We further show that using electron/positron beam polarizations can significantly improve the signal sensitivities. We find that the dimension-8 new physics scale can be probed up to the multi-TeV region at such lepton colliders.

hep-ph↗