Publications

2024

1. PRD

   Postinflationary Structure Formation Boosted by Parametric Self-Resonance

   Benedikt Eggemeier, Peter Hayman, Jens C. Niemeyer, and Richard Easther

   Physical Review D, Feb 2024

   Abs DOI

   The postinflationary Universe can pass through a long epoch of effective matter-dominated expansion. This era may allow for both the parametric amplification of initial fluctuations and the gravitational collapse of inflaton perturbations. We perform first-of-their-kind high-resolution simulations that span the resonant phase and subsequent gravitational collapse of the inflaton field by segueing from a full Klein-Gordon treatment of resonance to a computationally efficient Schrödinger-Poisson description that accurately captures the gravitational dynamics when most quanta are nonrelativistic. We consider a representative example in which resonance generates overdensities and gravitational collapse follows promptly as resonance ends. We observe the formation of solitonic cores inside inflaton halos and complex gravitational dynamics on scales of , greatly extending the possible scope of nonlinear postinflationary gravitational dynamics.

2. arxiv

   A Lean and Mean Introduction to Modern General Relativity

   Peter Hayman

   Dec 2024

   Abs

   Notes prepared for the introductory general relativity course PHYSICS 748 at The University of Auckland. They are designed to introduce general relativity to upper-year undergraduate students directly using the modern language of differential geometry but in a physically motivated way, and throughout keeping a logical flow from section to section and chapter to chapter. In doing so, they necessarily cover a number of topics either not normally treated in an introductory course, or from a novel perspective. These include for example: affine spaces, comparing and contrasting rank-2 tensors with matrices, integration on manifolds, the Rindler metric, including a proper near-source boundary condition for the Schwarzschild metric, approaching Kruskal-Szekeres coordinates from a Rindler perspective, and more.

3. arxiv

   A Purely Relativistic Point-Source Boundary Condition for the Schwarzschild Solution

   Peter Hayman

   Nov 2024

   Abs DOI

   We present a simple derivation of a point-source boundary condition for the Schwarzschild solution that relates the Schwarzschild radius to the mass of its source without appealing to the Newtonian limit. Interpretation of the Schwarzschild radius in terms of the mass of a point-like source traditionally means resorting to distant asymptotics and the safety of Newtonian gravity, but here we instead show a direct connection between a point-particle’s invariant mass and the length parameter of the Schwarzschild solution it sources, fully within the framework of general relativity. As a corollary, we also explain why attempts to show this by distributional techniques often result in a physically unmotivated spatial distribution for the source stress-energy tensor.

2022

1. J. Inst.

   Double-Hit Separation and dE/Dx Resolution of a Time Projection Chamber with GEM Readout

   Y. Aoki, D. Attié, T. Behnke, A. Bellerive, O. Bezshyyko, and 66 more authors

   Journal of Instrumentation, Nov 2022

   Abs DOI

   A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.

2021

1. PLA

   Nuclear Predictions for H Spectroscopy without Nuclear Errors

   C. P. Burgess, P. Hayman, Markus Rummel, and László Zalavári

   Physics Letters A, Feb 2021

   Abs DOI

   Nuclear-structure effects often provide an irreducible theory error that prevents using precision atomic measurements to test fundamental theory. We apply newly developed effective field theory tools to Hydrogen atoms, and use them to show that (to the accuracy of present measurements) all nuclear finite-size effects (e.g. the charge radius, Friar moments, nuclear polarizabilities, recoil corrections, Zemach moments etc.) only enter into atomic energies through exactly two parameters, independent of any nuclear-modeling uncertainties. Since precise measurements are available for more than two atomic levels in Hydrogen, this observation allows the use of precision atomic measurements to eliminate the theory error associated with nuclear matrix elements. We apply this reasoning to the seven atomic measurements whose experimental accuracy is smaller than 10 kHz to provide predictions for nuclear-size effects whose theoretical accuracy is not subject to nuclear-modeling uncertainties and so are much smaller than 1 kHz. Furthermore, the accuracy of these predictions can improve as atomic measurements improve, allowing precision fundamental tests to become possible well below the ‘irreducible’ error floor of nuclear theory.

2. Ann. Phys.

   Precision Nuclear-Spin Effects in Atoms: EFT Methods for Reducing Theory Errors

   L. Zalavari, C. P. Burgess, P. Hayman, and M. Rummel

   Annals of Physics, Jun 2021

   Abs DOI

   We use effective field theory to compute the influence of nuclear structure on precision calculations of atomic energy levels. As usual, the EFT’s effective couplings correspond to the various nuclear properties (such as the charge radius, nuclear polarizabilities, Friar and Zemach moments etc.) that dominate its low-energy electromagnetic influence on its surroundings. By extending to spinning nuclei the arguments developed for spinless ones in Burgess, et al. (2018), we use the EFT to show – to any fixed order in Zα (where Z is the atomic number and α the fine-structure constant) and the ratio of nuclear to atomic size – that nuclear properties actually contribute to electronic energies through fewer parameters than the number of these effective nuclear couplings naively suggests. Our result is derived using a position-space method for matching effective parameters to nuclear properties in the EFT, that more efficiently exploits the simplicity of the small-nucleus limit in atomic systems. By showing that precision calculations of atomic spectra depend on fewer nuclear uncertainties than naively expected, this observation allows the construction of many nucleus-independent combinations of atomic energy differences whose measurement can be used to test fundamental physics (such as the predictions of QED) because their theoretical uncertainties are not limited by the accuracy of nuclear calculations. We provide several simple examples of such nucleus-free predictions for Hydrogen-like atoms.

2019

1. Front. Phys.

   Point-Particle Catalysis

   Peter Hayman, and Cliff P. Burgess

   Frontiers in Physics, Jun 2019

   Abs DOI

   We use the point-particle effective field theory (PPEFT) framework to describe particle-conversion mediated by a flavour-changing coupling to a point-particle. We do this for a toy model of two non-relativistic scalars coupled to the same point-particle, on which there is a flavour-violating coupling. It is found that the point-particle couplings all must be renormalized with respect to a radial cut-off near the origin, and it is an invariant of the flow of the flavour-changing coupling that is directly related to particle-changing cross-sections. At the same time, we find an interesting dependence of those cross-sections on the ratio k_out/k_in of the outgoing and incoming momenta, which can lead to a 1/k_in enhancement in certain regimes. We further connect this model to the case of a single-particle non-self-adjoint (absorptive) PPEFT, as well as to a PPEFT of a single particle coupled to a two-state nucleus. These results could be relevant for future calculations of any more complicated reactions, such as nucleus-induced electron-muon conversions, monopole catalysis of baryon number violation, as well as nuclear transfer reactions.

2018

1. JHEP

   Reduced theoretical error for 4He+ spectroscopy

   C. P. Burgess, P. Hayman, Markus Rummel, and László Zalavári

   Physical Review A, Nov 2018

   Abs DOI

   We apply point-particle effective field theory to electronic and muonic 4He+ ions, and use it to identify linear combinations of spectroscopic measurements for which the theoretical uncertainties are much smaller than for any particular energy levels. The error is reduced because these combinations are independent of all short-range physics effects up to a given order in the expansion in the small parameters R/aB and Zα (where R and aB are the ion’s nuclear and Bohr radii). In particular, the theory error is not limited by the precision with which nuclear matrix elements can be computed, or compromised, by the existence of any novel short-range interactions, should these exist. These combinations of 4He measurements therefore provide particularly precise tests of quantum electrodynamics. The restriction to 4He arises because our analysis assumes a spherically symmetric nucleus, but the argument used is more general and extendable to both nuclei with spin, and to higher orders in R/aB and Zα.

2017

1. NIM-A

   A Time Projection Chamber with GEM-based Readout

   David Attié, Ties Behnke, Alain Bellerive, Oleg Bezshyyko, Deb Sankar Bhattacharya, and 64 more authors

   Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Jun 2017

   Abs DOI

   For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1T solenoidal field and read out with three independent Gas Electron Multiplier (GEM) based readout modules, are reported. The TPC was exposed to a 6GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.

2. JHEP

   Point-Particle Effective Field Theory I: Classical Renormalization and the Inverse-Square Potential

   C.P. Burgess, Peter Hayman, M. Williams, and László Zalavári

   Journal of High Energy Physics, Apr 2017

   Abs DOI

   Singular potentials (the inverse-square potential, for example) arise in many situations and their quantum treatment leads to well-known ambiguities in choosing boundary conditions for the wave-function at the position of the potential’s singularity. These ambiguities are usually resolved by developing a self-adjoint extension of the original prob-lem; a non-unique procedure that leaves undetermined which extension should apply in specific physical systems. We take the guesswork out of this picture by using techniques of effective field theory to derive the required boundary conditions at the origin in terms of the effective point-particle action describing the physics of the source. In this picture ambiguities in boundary conditions boil down to the allowed choices for the source action, but casting them in terms of an action provides a physical criterion for their determination. The resulting extension is self-adjoint if the source action is real (and involves no new degrees of freedom), and not otherwise (as can also happen for reasonable systems). We show how this effective-field picture provides a simple framework for understanding well-known renormalization effects that arise in these systems, including how renormalization-group techniques can resum non-perturbative interactions that often arise, particularly for non-relativistic applications. In particular we argue why the low-energy effective theory tends to produce a universal RG flow of this type and describe how this can lead to the phenomenon of reaction catalysis, in which physical quantities (like scattering cross sections) can sometimes be surprisingly large compared to the underlying scales of the source in question. We comment in passing on the possible relevance of these observations to the phenomenon of the catalysis of baryon-number violation by scattering from magnetic monopoles.

3. JHEP

   Point-Particle Effective Field Theory III: Relativistic Fermions and the Dirac Equation

   C. P. Burgess, Peter Hayman, Markus Rummel, and László Zalavári

   Journal of High Energy Physics, Sep 2017

   Abs DOI

   We formulate point-particle effective field theory (PPEFT) for relativistic spin-half fermions interacting with a massive, charged finite-sized source using a first-quantized effective field theory for the heavy compact object and a second-quantized language for the lighter fermion with which it interacts. This description shows how to determine the near-source boundary condition for the Dirac field in terms of the relevant physical properties of the source, and reduces to the standard choices in the limit of a point source. Using a first-quantized effective description is appropriate when the compact object is sufficiently heavy, and is simpler than (though equivalent to) the effective theory that treats the compact source in a second-quantized way. As an application we use the PPEFT to parameterize the leading energy shift for the bound energy levels due to finite-sized source effects in a model-independent way, allowing these effects to be fit in precision measurements. Besides capturing finite-source-size effects, the PPEFT treatment also efficiently captures how other short-distance source interactions can shift bound-state energy levels, such as due to vacuum polarization (through the Uehling potential) or strong interactions for Coulomb bound states of hadrons, or any hypothetical new short-range forces sourced by nuclei.

4. JHEP

   Point-Particle Effective Field Theory II: Relativistic Effects and Coulomb/Inverse-Square Competition

   C. P. Burgess, Peter Hayman, Markus Rummel, Matt Williams, and László Zalavári

   Journal of High Energy Physics, Jul 2017

   Abs DOI

   We apply point-particle effective field theory (PPEFT) to compute the leading shifts due to finite-sized source effects in the Coulomb bound energy levels of a relativistic spinless charged particle. This is the analogue for spinless electrons of calculating the contribution of the charge-radius of the source to these levels, and our calculation disagrees with standard calculations in several ways. Most notably we find there are two effective interactions with the same dimension that contribute to leading order in the nuclear size, one of which captures the standard charge-radius contribution. The other effective operator is a contact interaction whose leading contribution to δE arises linearly (rather than quadratically) in the small length scale, ε, characterizing the finite-size effects, and is suppressed by (Zα)5. We argue that standard calculations miss the contributions of this second operator because they err in their choice of boundary conditions at the source for the wave-function of the orbiting particle. PPEFT predicts how this boundary condition depends on the source’s charge radius, as well as on the orbiting particle’s mass. Its contribution turns out to be crucial if the charge radius satisfies ε \lessequivlnt (Zα)2 a B , where a B is the Bohr radius, because then relativistic effects become important for the boundary condition. We show how the problem is equivalent to solving the Schrödinger equation with competing Coulomb, inverse-square and delta-function potentials, which we solve explicitly. A similar enhancement is not predicted for the hyperfine structure, due to its spin-dependence. We show how the charge-radius effectively runs due to classical renormalization effects, and why the resulting RG flow is central to predicting the size of the energy shifts (and is responsible for its being linear in the source size). We discuss how this flow is relevant to systems having much larger-than-geometric cross sections, such as those with large scattering lengths and perhaps also catalysis of reactions through scattering with monopoles. Experimental observation of these effects would require more precise measurement of energy levels for mesonic atoms than are now possible.

2016

1. JCAP

   Magnon Inflation: Slow Roll with Steep Potentials

   Peter Adshead, Diego Blas, C. P. Burgess, Peter Hayman, and Subodh P. Patil

   Journal of Cosmology and Astroparticle Physics, Nov 2016

   Abs DOI

   We find multi-scalar effective field theories (EFTs) that can achieve a slow inflationary roll despite having a scalar potential that does not satisfy Gab ∂a V ∂b V ≪ V2/Mp2 (where Gab is the target-space metric). They evade the usual slow-roll conditions on V because their kinetic energies are dominated by single-derivative terms rather than the usual two-derivative terms. Single derivatives dominate during slow roll and so do not require a breakdown of the usual derivative expansion that underpins calculational control in much of cosmology. The presence of such terms requires some sort of UV Lorentz-symmetry breaking during inflation (besides the usual cosmological breaking). Chromo-natural inflation provides one particular example of a UV theory that can generate the multi-field single-derivative terms we consider, and we argue that the EFT we find indeed captures the slow-roll conditions for its background evolution. We also show that our EFT can be understood as a multi-field generalization of the single-field Cuscuton models. The multi-field case introduces a new feature, however: the scalar kinetic terms define a target-space 2-form, Fab, whose antisymmetry gives new ways for slow roll to be achieved.

2. JCAP

   Goldilocks Models of Higher-Dimensional Inflation (Including Modulus Stabilization)

   C. P. Burgess, Jared J. H. Enns, Peter Hayman, and Subodh P. Patil

   Journal of Cosmology and Astroparticle Physics, Aug 2016

   Abs DOI

   We explore the mechanics of inflation within simplified extra-dimensional models involving an inflaton interacting with the Einstein-Maxwell system in two extra dimensions. The models are Goldilocks-like inasmuch as they are just complicated enough to include a mechanism to stabilize the extra-dimensional size (or modulus), yet simple enough to solve explicitly the full extra-dimensional field equations using only simple tools. The solutions are not restricted to the effective 4D regime with H ≪ mKK (the latter referring to the characteristic mass splitting of the Kaluza-Klein excitations) because the full extra-dimensional Einstein equations are solved. This allows an exploration of inflationary physics in a controlled calculational regime away from the usual four-dimensional lamp-post. The inclusion of modulus stabilization is important because experience with string models teaches that this is usually what makes models fail: stabilization energies easily dominate the shallow potentials required by slow roll and so open up directions to evolve that are steeper than those of the putative inflationary direction. We explore (numerically and analytically) three representative kinds of inflationary scenarios within this simple setup. In one the radion is trapped in an inflaton-dependent local minimum whose non-zero energy drives inflation. Inflation ends as this energy relaxes to zero when the inflaton finds its own minimum. The other two involve power-law scaling solutions during inflation. One of these is a dynamical attractor whose features are relatively insensitive to initial conditions but whose slow-roll parameters cannot be arbitrarily small; the other is not an attractor but can roll much more slowly, until eventually transitioning to the attractor. The scaling solutions can satisfy H > mKK, but when they do standard 4D fluctuation calculations need not apply. When in a 4D regime the solutions predict η ≃ 0 and so r ≃ 0.11 when ns ≃ 0.96 and so are ruled out if tensor modes remain unseen. Assessment of general parameters is difficult until a full 6D fluctuation calculation is done.