arXiv subjects

John McDonald

Publications and source records attributed to John McDonald.

At least 37 records · Page 2Linked to original sources

arXiv2021

A 2.5D Vehicle Odometry Estimation for Vision Applications

This paper proposes a method to estimate the pose of a sensor mounted on a vehicle as the vehicle moves through the world, an important topic for autonomous driving systems. Based on a set of commonly deployed vehicular odometric sensors, with outputs available on automotive communication buses (e.g. CAN or FlexRay), we describe a set of steps to combine a planar odometry based on wheel sensors with a suspension model based on linear suspension sensors. The aim is to determine a more accurate estimate of the camera pose. We outline its usage for applications in both visualisation and computer vision.

cs.RO↗

arXiv2021

Computer vision in automated parking systems: Design, implementation and challenges

Automated driving is an active area of research in both industry and academia. Automated Parking, which is automated driving in a restricted scenario of parking with low speed manoeuvring, is a key enabling product for fully autonomous driving systems. It is also an important milestone from the perspective of a higher end system built from the previous generation driver assistance systems comprising of collision warning, pedestrian detection, etc. In this paper, we discuss the design and implementation of an automated parking system from the perspective of computer vision algorithms. Designing a low-cost system with functional safety is challenging and leads to a large gap between the prototype and the end product, in order to handle all the corner cases. We demonstrate how camera systems are crucial for addressing a range of automated parking use cases and also, to add robustness to systems based on active distance measuring sensors, such as ultrasonics and radar. The key vision modules which realize the parking use cases are 3D reconstruction, parking slot marking recognition, freespace and vehicle/pedestrian detection. We detail the important parking use cases and demonstrate how to combine the vision modules to form a robust parking system. To the best of the authors' knowledge, this is the first detailed discussion of a systemic view of a commercial automated parking system.

cs.CV↗

arXiv2021

Vision-based Driver Assistance Systems: Survey, Taxonomy and Advances

Vision-based driver assistance systems is one of the rapidly growing research areas of ITS, due to various factors such as the increased level of safety requirements in automotive, computational power in embedded systems, and desire to get closer to autonomous driving. It is a cross disciplinary area encompassing specialised fields like computer vision, machine learning, robotic navigation, embedded systems, automotive electronics and safety critical software. In this paper, we survey the list of vision based advanced driver assistance systems with a consistent terminology and propose a taxonomy. We also propose an abstract model in an attempt to formalize a top-down view of application development to scale towards autonomous driving system.

cs.RO↗

arXiv2020

Sub-Planckian $ϕ^{2}$ Inflation in the Palatini Formulation of Gravity with an $R^2$ term

In the context of the Palatini formalism of gravity with an $R^{2}$ term, a $ϕ^{2}$ potential can be consistent with the observed bound on $r$ whilst retaining the successful prediction for $n_{s}$. Here we show that the Palatini $ϕ^{2} R^2$ inflation model can also solve the super-Planckian inflaton problem of $ϕ^{2}$ chaotic inflation, and that the model can be consistent with Planck scale-suppressed potential corrections. If $α\gtrsim 10^{12}$, where $α$ is the coefficient of the $R^2$ term, the inflaton in the Einstein frame, $σ$, remains sub-Planckian throughout inflation. In addition, if $α\gtrsim 10^{20}$ then the predictions of the model are unaffected by Planck-suppressed potential corrections in the case where there is a broken shift symmetry, and if $α\gtrsim 10^{32}$ then the predictions are unaffected by Planck-suppressed potential corrections in general. The value of $r$ is generally small, with $r \lesssim 10^{-5}$ for $α\gtrsim 10^{12}$. We calculate the maximum possible reheating temperature, $T_{R\;max}$, corresponding to instantaneous reheating. For $α\approx 10^{32}$, $T_{R\; max}$ is approximately $10^{10}$ GeV, with larger values of $T_{R\;max}$ for smaller $α$. For the case of instantaneous reheating, we show that $n_{s}$ is in agreement with the 2018 Planck results to within 1-$σ$, with the exception of the $α\approx 10^{32}$ case, which is close to the 2-$σ$ lower bound. Following inflation, the inflaton condensate is likely to rapidly fragment and form oscillons. Reheating via inflaton decays to right-handed neutrinos can easily result in instantaneous reheating. We determine the scale of unitarity violation and show that, in general, unitarity is conserved during inflation.

hep-ph↗

arXiv2019

The KSVZ Axion Model with Quasi-Degenerate Minima: A Unified Model for Dark Matter and Dark Energy

We consider the possibility that dark matter and dark energy can be explained by the minimal KSVZ axion model. This is possible if the lowest energy metastable minimum of the scalar potential has zero energy density, which is possible in theoretical models of vacuum energy cancellation based on spacetime averaging and in models based on energy parity. Dark energy is then understood as being due to the energy density of the metastable electroweak vacuum relative to a second quasi-degenerate metastable minimum. The requirement of quasi-degenerate minima is a non-trivial condition which completely determines the form of the potential for a given value of the axion decay constant, $f_{a}$, and the PQ scalar self-coupling, $λ_ϕ$. The existence of the second quasi-degenerate minimum imposes a new lower bound on the axion decay constant, $f_{a} \geq 2.39 \times 10^{10} \, λ_ϕ^{-1/4}$ GeV. If the PQ symmetry is broken after inflation then the lower bound on $f_{a}$ implies a lower bound on the amount of axion dark matter, $Ω_{a}/Ω_{dm} \geq (0.28-0.46)\,λ_ϕ^{-0.291}$, where the range is due to the uncertainty in the amount of axion dark matter produced by vacuum realignment, cosmic strings and domain walls, therefore at least 30$\%$ of dark matter must be due to axions if $λ_ϕ \lesssim 1$. When axions constitute all of the dark matter and the PQ symmetry is broken after inflation, $f_{a}$, and so the form of the scalar potential, is completely fixed for a given value of $λ_ϕ$, with only a weak dependence on $λ_ϕ$. This will allow the inflation and post-inflation evolution of the model to be quantitatively studied for a given inflation model and dimensionally natural values of $λ_ϕ$.

hep-ph↗

arXiv2018

Freeze-In Dark Matter from a sub-Higgs Mass Clockwork Sector via the Higgs Portal

The clockwork mechanism allows extremely weak interactions and small mass scales to be understood in terms of the structure of a theory. A natural application of the clockwork mechanism is to the freeze-in mechanism for dark matter production. Here we consider a Higgs portal freeze-in dark matter model based on a scalar clockwork sector with a mass scale which is less than the Higgs boson mass. The dark matter scalar is the lightest scalar of the clockwork sector. Freeze-in dark matter is produced by the decay of thermal Higgs bosons to the clockwork dark matter scalars. We show that the mass of the dark matter scalar is typically in the 1-10 keV range and may be warm enough to have an observable effect on perturbation growth and Lyman-$α$ observations. Clockwork Higgs portal freeze-in models have a potentially observable collider phenomenology, with the Higgs boson decaying to missing energy in the form of pairs of long-lived clockwork sector scalars, plus a distribution of different numbers of quark and lepton particle-antiparticle pairs. The branching ratio to different numbers of quark and lepton pairs is determined by the clockwork sector parameters (the number of clockwork scalars $N$ and the clockwork charge $q$), which could therefore be determined experimentally if such Higgs decay modes are observed. In the case of a minimal Standard Model observable sector, the combination of nucleosynthesis and Lyman-$α$ constraints is likely to exclude on-shell Higgs decays to clockwork scalars, although off-shell Higgs decays would still be possible. On-shell Higgs decays to clockwork scalars can be consistent with cosmological constraints in simple extensions of the Standard Model with light singlet scalars.

hep-ph↗

arXiv2018

Clockwork Higgs portal model for freeze-in dark matter

The clockwork mechanism can explain interactions which are dimensionally very weak without the need for very large mass scales. We present a model in which the clockwork mechanism generates the very small Higgs portal coupling and dark matter particle mass necessary to explain cold dark matter via the freeze-in mechanism. We introduce a TeV-scale scalar clockwork sector which couples to the Standard Model via the Higgs portal. The dark matter particle is the lightest scalar of the clockwork sector. We show that the freeze-in mechanism is dominated by decay of the heavy clockwork scalars to light dark matter scalars and Higgs bosons. In the model considered, we find that freeze-in dark matter is consistent with the clockwork mechanism for global charge $q$ in the range $2 \lesssim q \lesssim 4$ when the number of massive scalars is in the range $10 \leq N \leq 20$. The dark matter scalar mass and portal coupling are independent of $q$ and $N$. For a typical TeV-scale clockwork sector, the dark matter scalar mass is predicted to be of the order of a MeV.

hep-ph↗

arXiv2018

Chaotic initial conditions for nonminimally coupled inflation via a conformal factor with a zero

Nonminimally coupled inflation models based on a nonminimal coupling $ξϕ^{2} R$ and a $ϕ^{4}$ potential are in excellent agreement with the scalar spectral index observed by Planck. Here we consider the modification of these models by a conformal factor with a zero. This enables a nonminimally coupled model to have a Planck-scale potential energy density at large values of the inflaton field, which can account for the smooth, potential-dominated volume that is necessary for inflation to start. We show that models with a conformal factor zero generally predict a correlated increase of the spectral index $n_{s}$ and tensor-to-scalar ratio $r$. For values of $n_{s}$ that are within the present $2-σ$ bounds from Planck, modification by $Δr$ as large as 0.0013 is possible, which is large enough to be measured by next generation cosmic microwave background polarization satellites.

astro-ph.CO↗

arXiv2018

Inflaton condensate fragmentation: Analytical conditions and application to $α$-attractor models

We study the stability of an inflaton condensate in the presence of attractive inflaton self-interactions, in order to determine analytical conditions on the self-interaction couplings under which the condensate undergoes fragmentation. As an application of our results, we consider the stability of the inflaton condensate in $α$-attractor inflation. We show that the stability of the condensate depends upon the value of $α$. For the T-model with $n = 1$, we find that it is unstable for $α\lesssim 10^{-4}$. In this case it is expected that inflation will be followed by an oscillon-dominated era.

astro-ph.CO↗

arXiv2016

Warm Dark Matter via Ultra-Violet Freeze-In: Reheating Temperature and Non-Thermal Distribution for Fermionic Higgs Portal Dark Matter

Warm dark matter (WDM) of order keV mass may be able to resolve the disagreement between structure formation in cold dark matter simulations and observations. The detailed properties of WDM will depend upon its energy distribution, in particular how it deviates from the thermal distribution usually assumed in WDM simulations. Here we focus on WDM production via the Ultra-Violet (UV) freeze-in mechanism, for the case of fermionic Higgs portal dark matter $ψ$ produced via the portal interaction $\barψψH^{\dagger}H/Λ$. We introduce a new method to simplify the computation of the non-thermal energy distribution of dark matter from freeze-in. We show that the non-thermal energy distribution from UV freeze-in is hotter than the corresponding thermal distribution and has the form of a Bose-Einstein distribution with a non-thermal normalization. The resulting range of dark matter fermion mass consistent with observations is 5-7 keV. The reheating temperature must satisfy $T_{R} \gtrsim 120 $ GeV in order to account for the observed dark matter density when $m_ψ \approx 5 $ keV, where the lower bound on $T_{R}$ corresponds to the limit where the fermion mass is entirely due to electroweak symmetry breaking via the portal interaction. The corresponding bound on the interaction scale is $Λ\gtrsim 6.0 \times 10^{9}$ GeV.

hep-ph↗

arXiv2016

Non-Minimally Coupled Inflation with Initial Conditions from a Pre-Inflation Anamorphic Contracting Era

Inflation due to a non-minimally coupled scalar field with a large non-minimal coupling, as first proposed by Salopek, Bardeen and Bond (SBB), is in good agreement with the observed value of the spectral index and constraints on the tensor-to-scalar ratio. Here we explore the possibility that SBB inflation represents the late stage of a Universe which emerges from an early contracting era. We present a model in which the Universe smoothly transitions from an anamorphic contracting era to late-time SBB inflation without encountering a singular bounce. This corresponds to a continuous expansion in the Einstein frame throughout. We show that the anamorphic contracting era is able to provide the smooth superhorizon initial conditions necessary for subsequent SBB inflation to occur. The model predicts corrections to the non-minimal coupling, kinetic term and potential of SBB inflation which can observably increase the observed spectral index relative to its SBB prediction.

astro-ph.CO↗

arXiv2015

WIMP Dark Matter and Unitarity-Conserving Inflation via a Gauge Singlet Scalar

A gauge singlet scalar with non-minimal coupling to gravity can drive inflation and later freeze out to become cold dark matter. We explore this idea by revisiting inflation in the singlet direction (S-inflation) and Higgs Portal Dark Matter in light of the Higgs discovery, limits from LUX and observations by Planck. We show that large regions of parameter space remain viable, so that successful inflation is possible and the dark matter relic abundance can be reproduced. Moreover, the scalar singlet can stabilise the electroweak vacuum and at the same time overcome the problem of unitarity-violation during inflation encountered by Higgs Inflation, provided the singlet is a real scalar. The 2-$σ$ Planck upper bound on $n_s$ imposes that the singlet mass is below 2 TeV, so that almost the entire allowed parameter range can be probed by XENON1T.

astro-ph.CO↗

arXiv2015

Signatures of Planck Corrections in a Spiralling Axion Inflation Model

The minimal sub-Planckian axion inflation model accounts for a large scalar-to-tensor ratio via a spiralling trajectory in the field space of a complex field $Φ$. Here we consider how the predictions of the model are modified by Planck scale-suppressed corrections. In the absence of Planck corrections the model is equivalent to a $ϕ^{4/3}$ chaotic inflation model. Planck corrections become important when the dimensionless coupling $ξ$ of $|Φ|^{2}$ to the topological charge density of the strongly-coupled gauge sector $F \tilde{F}$ satisfies $ξ\sim 1$. For values of $|Φ|$ which allow the Planck corrections to be understood via an expansion in powers of $|Φ|^{2}/M_{Pl}^{2}$, we show that their effect is to produce a significant modification of the tensor-to-scalar ratio from its $ϕ^{4/3}$ chaotic inflation value without strongly modifying the spectral index. In addition, to leading order in $|Φ|^2/M_{Pl}^{2}$, the Planck modifications of $n_{s}$ and $r$ satisfy a consistency relation, $Δn_{s} = - Δr/16$. Observation of these modifications and their correlation would allow the model to be distinguished from a simple $ϕ^{4/3}$ chaotic inflation model and would also provide a signature for the influence of leading-order Planck corrections.

hep-ph↗

arXiv2015

Simultaneous Generation of WIMP Miracle-like Densities of Baryons and Dark Matter

The observed density of dark matter is of the magnitude expected for a thermal relic weakly-interacting massive particle (WIMP). In addition, the observed baryon density is within an order of magnitude of the dark matter density. This suggests that the baryon density is physically related to a typical thermal relic WIMP dark matter density. We present a model which simultaneously generates thermal relic WIMP-like densities for both baryons and dark matter by modifying a large initial baryon asymmetry. Dark matter is due to O(100) GeV gauge singlet scalars produced in the annihilation of the O(TeV) coloured scalars which are responsible for the final thermal WIMP-like baryon asymmetry. The requirement of no baryon washout implies that there are two gauge singlet scalars. The low temperature transfer of the asymmetry to conventional baryons can be understood if the long-lived O(TeV) coloured scalars have large hypercharge, |Y| > 4/3. Production of such scalars at the LHC would be a clear signature of the model.

hep-ph↗

arXiv2015

A Minimal Sub-Planckian Axion Inflation Model with Large Tensor-to-Scalar Ratio

We present a minimal axion inflation model which can generate a large tensor-to-scalar ratio while remaining sub-Planckian. The modulus of a complex scalar field $Φ$ with a $λ|Φ|^4$ potential couples directly to the gauge field of a strongly-coupled sector via a term of the form $(|Φ|/M_{Pl})^{m} F \tilde{F}$. This generates a minimum of the potential which is aperiodic in the phase. The resulting inflation model is equivalent to a $ϕ^{4/(m+1)}$ chaotic inflation model. For the natural case of a leading-order portal-like interaction $Φ^{\dagger}ΦF \tilde{F}$, the model is equivalent to a $ϕ^{4/3}$ chaotic inflation model and predicts a tensor-to-scalar ratio $r = 16/3N = 0.097$ and a scalar spectral index $n_{s} = 1-5/3N = 0.970$. The value of $|Φ|$ remains sub-Planckian throughout the observable era of inflation, with $|Φ| \lesssim 0.01 M_{Pl}$ for $N \lesssim 60$ when $λ\sim 1$.

hep-ph↗

arXiv2014

Sub-Planckian Two-Field Inflation Consistent with the Lyth Bound

The BICEP2 observation of a large tensor-to-scalar ratio, $r = 0.20^{+0.07}_{-0.05}$, implies that the inflaton $ϕ$ in single-field inflation models must satisfy $ϕ\sim 10M_{Pl}$ in order to produce sufficient inflation. This is a problem if interaction terms suppressed by the Planck scale impose a bound $ϕ\; ^{<}_{\sim} \; M_{Pl}$. Here we consider whether it is possible to have successful sub-Planckian inflation in the case of two-field inflation. The trajectory in field space cannot be radial if the effective single-field inflaton is to satisfy the Lyth bound. By considering a complex field $Φ$, we show that a near circular but aperiodic modulation of a $|Φ|^{4}$ potential can reproduce the results of $ϕ^2$ chaotic inflation for $n_{s}$ and $r$ while satisfying $|Φ|\; ^{<}_{\sim} \; 0.01 M_{Pl}$ throughout. More generally, for models based on a $|Φ|^{4}$ potential, the simplest sub-Planckian models are equivalent to $ϕ^{2}$ and $ϕ^{4/3}$ chaotic inflation.

hep-ph↗

arXiv2014

Negative Running of the Spectral Index, Hemispherical Asymmetry and the Consistency of Planck with Large $r$

Planck favours a negative running of the spectral index, with the likelihood being dominated by low multipoles $l \lesssim 50$ and no preference for running at higher $l$. A negative spectral index is also necessary for the 2-$σ$ Planck upper bound on the tensor-to-scalar ratio $r$ to be consistent with values significantly larger than 0.1. Planck has also observed a hemispherical asymmetry of the CMB power spectrum, again mostly at low multipoles. Here we consider whether the physics responsible for the hemispherical asymmetry could also account for the negative running of the spectral index and the consistency of Planck with a large value of $r$. A negative running of the spectral index can be generated if the hemispherical asymmetry is due to a scale- and space-dependent modulation which suppresses the CMB power spectrum at low multipoles. We show that the observed hemispherical asymmetry at low $l$ can be generated while satisfying constraints on the asymmetry at higher $l$ and generating a negative spectral index of the right magnitude to account for the Planck observation and to allow Planck to be consistent with a large value of $r$.

astro-ph.CO↗

arXiv2014

Hemispherical Power Asymmetry from a Space-Dependent Component of the Adiabatic Power Spectrum

The hemispherical power asymmetry observed by Planck and WMAP can be interpreted as due to a spatially-varying and scale-dependent component of the adiabatic power spectrum. We derive general constraints on the magnitude and scale-dependence of a component with a dipole spatial variation. The spectral index and the running of the spectral index can be significantly shifted from their inflation model values, resulting in a smaller spectral index and a more positive running. A key prediction is a hemispherical asymmetry of the spectral index and of its running. Measurement of these asymmetries can test the structure of the perturbation responsible for the CMB power asymmetry.

astro-ph.CO↗