arXiv subjects

Lauren Pearce

Publications and source records attributed to Lauren Pearce.

At least 19 recordsLinked to original sources

arXiv2025

Using Gravitational Wave Signals to Disentangle Early Matter Dominated Epochs

Curvature perturbations induce gravitational waves (GWs) at second order, contributing to the stochastic gravitational wave background. The resulting gravitational wave spectrum is sensitive to the evolutionary history of the universe and can be substantially enhanced by early matter-dominated (eMD) epochs, particularly if they end rapidly. Such epochs can be caused by primordial black holes (PBHs) and non-topological solitons (Q-balls), for example. Prior analysis approximated the end of the eMD epoch as instantaneous or used a Gaussian smoothing. In this work, we present a complete analysis fully incorporating their time-evolving decay rates. We demonstrate that the resulting signal spectra from PBH, thin wall Q-ball, thick wall Q-ball, and delayed Q-ball eMD epochs are distinguishable for monochromatic distributions. We then consider log-normal mass distributions and discuss the distinguishability of the various GW spectra. Importantly we find that the change in the spectrum from a finite mass width is qualitatively different from the change arising from a slower transition to radiation domination.

astro-ph.CO↗

arXiv2024

Conversations and Deliberations: Non-Standard Cosmological Epochs and Expansion Histories

This document summarizes the discussions which took place during the PITT-PACC Workshop entitled "Non-Standard Cosmological Epochs and Expansion Histories," held in Pittsburgh, Pennsylvania, Sept. 5-7, 2024. Much like the non-standard cosmological epochs that were the subject of these discussions, the format of this workshop was also non-standard. Rather than consisting of a series of talks from participants, with each person presenting their own work, this workshop was instead organized around free-form discussion blocks, with each centered on a different overall theme and guided by a different set of Discussion Leaders. This document is not intended to serve as a comprehensive review of these topics, but rather as an informal record of the discussions that took place during the workshop, in the hope that the content and free-flowing spirit of these discussions may inspire new ideas and research directions.

astro-ph.CO↗

arXiv2024

Gravitational Wave Signals From Early Matter Domination: Interpolating Between Fast and Slow Transitions

An epoch of matter domination in the early universe can enhance the primordial stochastic gravitational wave signal, potentially making it detectable to upcoming gravitational wave experiments. However, the resulting gravitational wave signal is quite sensitive to the end of the early matter-dominated epoch. If matter domination ends gradually, a cancellation results in an extremely suppressed signal, while in the limit of an instantaneous transition, there is a resonant-like enhancement. The end of the matter dominated epoch cannot be instantaneous, however, and previous analyses have used a Gaussian smoothing technique to account for this, and consider only a limited regime around the fast transition limit. In this work, we present a study of the enhanced gravitational wave signal from early matter domination without making either approximation and show how the signal smoothly evolves from the strongly suppressed to strongly enhanced regimes.

astro-ph.CO↗

arXiv2023

Fireball baryogenesis from early structure formation due to Yukawa forces

We show that viable electroweak baryogenesis can be realized without a first-order phase transition if plasma is heated inhomogeneously by nongravitational structure formation in some particle species. Yukawa interactions can mediate relatively long-range attractive forces in the early Universe. This creates an instability and leads to growth of structure in some species even during the radiation dominated era. At temperatures below the electroweak scale, the collapsing and annihilating halos can heat up plasma in fireballs that expand and create the out-of-equilibrium high-temperature environment suitable for generating the baryon asymmetry. The plasma temperature at the time of baryogenesis can be as low as a few MeV, making it consistent with both standard and low-reheat cosmologies.

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arXiv2023

Testing high scale supersymmetry via second order gravitational waves

Supersymmetry predicts multiple flat directions, some of which carry a net baryon or lepton number. Condensates in such directions form during inflation and later fragment into Q-balls, which can become the building blocks of primordial black holes. Thus supersymmetry can create conditions for an intermediate matter-dominated era with black holes dominating the energy density of the universe. Unlike particle matter, black holes decay suddenly enough to result in an observable gravitational wave signal via the poltergeist mechanism. We investigate the gravitational waves signatures of supersymmetry realized at energy scales that might not be accessible to present-day colliders.

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arXiv2022

Generating Non-topological Solitons Via Thermal Corrections: Higgs Balls

Scalar fields which carry charge can generally form non-topoligical solitons (Q-balls), if the energy in the extended configuration is less than the energy of an equivalent number of free quanta. For global Q-balls, such solitons exist whenever the potential grows slower than quadratically. We show that even in the absence of attractive interactions, finite temperature corrections can generate Q-ball solutions, as the coefficient of cubic corrections is generally negative. As an illustration of this, we consider the possibility of constructing Q-balls using the Higgs field. We first show that the finite temperature corrections would enable the existence of Higgs balls if the Standard Model symmetry was ungauged. We then show that Higgs self-interactions mediated by the Standard Model gauge bosons are sufficient to prevent the existence of these states in the actual Standard Model, but they can be present in a variety of extensions.

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arXiv2021

Detectable Gravitational Wave Signals from Affleck-Dine Baryogenesis

In Affleck-Dine baryogenesis, the observed baryon asymmetry of the Universe is generated through the evolution of the vacuum expectation value (VEV) of a scalar condensate. This scalar condensate generically fragments into non-topological solitons (Q-balls). If they are sufficiently long-lived, they lead to an early matter domination epoch, which enhances the primordial gravitational wave signal for modes that enter the horizon during this epoch. The sudden decay of the Q-balls into fermions results in a rapid transition from matter to radiation domination, producing a sharp peak in the gravitational wave power spectrum. Avoiding the problem of gravitino over-abundance favours scenarios where the peak frequency of the resonance is within the range of the Einstein Telescope and/or Decigo. Therefore, we show this scenario provides an observable signal, providing a mechanism to test Affleck-Dine baryogenesis.

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arXiv2020

Stochastic evolution of scalar fields with continuous symmetries during inflation

During inflation, scalar fields with masses less than the Hubble scale acquire vacuum expectation values (vevs) via stochastic processes driven by quantum fluctuations. For nearly massless spectator scalars transforming nontrivially under a continuous symmetry group, we demonstrate that the evolution of the vev depends on the dimensionality of the scalar field space. Fields in larger representations both attain larger vacuum expectation values and converge more rapidly to equilibrium. We present an argument demonstrating how this higher-dimensional evolution can be obtained in unitary gauge for fields transforming under local symmetries with a mass gap that is small compared to the Hubble scale. Finally, we show that accounting for the full number of degrees of freedom in the Standard Model Higgs multiplet tightens Higgs stability constraints on the inflationary scale at the percent level and has more dramatic consequences for both the vev and the energy stored in the Higgs field after inflation.

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arXiv2019

Phenomenology of fermion production during axion inflation

We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.

astro-ph.CO↗

arXiv2019

Gravitational waves from fermion production during axion inflation

We present analytic results for the gravitational wave power spectrum induced in models where the inflaton is coupled to a fermionic pseudocurrent. We show that although such a coupling creates helically polarized fermions, the polarized component of the resulting gravitational waves is parametrically suppressed with respect to the non-polarized one. We also show that the amplitude of the gravitational wave signal associated to this production cannot exceed that generated by the standard mechanism of amplification of vacuum fluctuations. We previously found that this model allows for a regime in which the backreaction of the produced fermions allows for slow-roll inflation even for a steep inflaton potential, and still leads to Gaussian primordial scalar perturbations. The present analysis shows that this regime also results in a gravitational wave signal compatible with the current bounds.

astro-ph.CO↗

arXiv2017

Resonant particle production during inflation: a full analytical study

We revisit the study of the phenomenology associated to a burst of particle production of a field whose mass is controlled by the inflaton field and vanishes at one given instance during inflation. This generates a bump in the correlators of the primordial scalar curvature. We provide a unified formalism to compute various effects that have been obtained in the literature and confirm that the dominant effects are due to the rescattering of the produced particles on the inflaton condensate. We improve over existing results (based on numerical fits) by providing exact analytic expressions for the shape and height of the bump, both in the power spectrum and the equilateral bispectrum. We then study the regime of validity of the perturbative computations of this signature. Finally, we extend these computations to the case of a burst of particle production in a sector coupled only gravitationally to the inflaton.

astro-ph.CO↗

arXiv2017

Relaxation leptogenesis, isocurvature perturbations, and the cosmic infrared background

Observations of cosmic infrared background (CIB) radiation exhibit significant fluctuations on small angular scales. A number of explanations have been put forth, but there is currently no consensus on the origin of these large fluctuations. We consider the possibility that small-scale fluctuations in matter-antimatter asymmetry could lead to variations in star formation rates which are responsible for the CIB fluctuations. We show that the recently proposed Higgs relaxation leptogenesis mechanism can produce such small-scale baryonic isocurvature perturbations which can explain the observed excess in the CIB fluctuations.

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arXiv2016

The phenomenology of trapped inflation

Trapped inflation is a mechanism in which particle production from the moving inflaton is the main source of friction in the inflaton equation of motion. The produced fields source inflaton perturbations, which dominate over the vacuum ones. We employ the set of equations for the inflaton zero mode and its perturbations which was developed in the original work on trapped inflation, and which we extend to second order in the perturbations. We build on this study by updating the experimental constraints, and by replacing the existing approximate solutions with more accurate ones. We obtain a different numerical value for the amplitude of the scalar power spectrum, and a parametrically different result for the bispectrum. This has implications for the allowed region of parameter space in models of trapped inflation, and for some of the phenomenological results obtained in this region. The main results in the allowed region are the following: monomial inflaton potentials, such as $V \propto φ,\, φ^2$ can be compatible with the data, and (in a portion of the allowed region) the inflaton can be sub-Planckian over all the "observable" stage of inflation; gravitational waves from this mechanism are too small to be observed in the foreseeable future; a non-gaussianity parameter $-60 < f_{\rm NL} < -20 $ is obtained in the allowed region for exactly equilateral configurations, with a mild dependence on the parameters of the model and of the inflaton potential.

astro-ph.CO↗

arXiv2016

Baryogenesis via Elementary Goldstone Higgs Relaxation

We extend the relaxation mechanism to the Elementary Goldstone Higgs framework. Besides studying the allowed parameter space of the theory we add the minimal ingredients needed for the framework to be phenomenologically viable. The very nature of the extended Higgs sector allows to consider very flat scalar potential directions along which the relaxation mechanism can be implemented. This fact translates into wider regions of applicability of the relaxation mechanism when compared to the Standard Model Higgs case. Our results show that, if the electroweak scale is not fundamental but radiatively generated, it is possible to generate the observed matter-antimatter asymmetry via the relaxation mechanism.

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arXiv2016

Leptogenesis via the 750 GeV pseudoscalar

Recently the ATLAS and CMS collaborations have reported evidence of a diphoton excess which may be interpreted as a pseudoscalar boson S with a mass around 750 GeV. To explain the diphoton excess, such a boson is coupled to the Standard Model gauge fields via SFF-dual operators. In this work, we consider the implications of this state for early universe cosmology; in particular, the S field can acquire a large vacuum expectation value due to quantum fluctuations during inflation. During reheating, it then relaxes to its equilibrium value, during which time the same operators introduced to explain the diphoton excess induce a nonzero chemical potential for baryon and lepton number. Interactions such as those involving right-handed neutrinos allow the system to develop a non-zero lepton number, and therefore, this state may also be responsible for the observed cosmological matter-antimatter asymmetry.

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arXiv2015

Leptogenesis via Higgs Condensate Relaxation

An epoch of Higgs relaxation may occur in the early universe during or immediately following postinflationary reheating. It has recently been pointed out that leptogenesis may occur in minimal extensions of the Standard Model during this epoch. We analyse Higgs relaxation taking into account the effects of perturbative and non-perturbative decays of the Higgs condensate, and we present a detailed derivation of the relevant kinetic equations and of the relevant particle interaction cross sections. We identify the parameter space in which a sufficiently large asymmetry is generated.

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arXiv2015

Leptogenesis Via Neutrino Production During Higgs Condensate Relaxation

During inflation, scalar fields, including the Higgs boson, may acquire a nonzero vacuum expectation value, which must later relax to the equilibrium value during reheating. In the presence of the time-dependent condensate, the vacuum state can evolve into a state with a nonzero particle number. We show that, in the presence of lepton number violation in the neutrino sector, the particle production can explain the observed matter-antimatter asymmetry of the universe. We find that this form of leptogenesis is particularly effective when the Higgs condensate decays rapidly and at low reheat scale. As part of the calculation, we present some exact results for the Bogoliubov transformations for Majorana fermions with a nonzero time-dependent chemical potential, in addition to a time-dependent mass.

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arXiv2015

Signals from dark atom formation in halos

We consider indirect detection signals of atomic dark matter, with a massive dark photon which mixes kinetically with hypercharge. In significant regions of parameter space, dark matter remains at least partially ionized today, and dark atom formation can occur efficiently in dense regions, such as the centers of galactic halos. The formation of dark atoms is accompanied by emission of a dark photon, which can subsequently decay into Standard Model particles. We discuss the expected signal strength and compare it to that of annihilating dark matter. As a case study, we explore the possibility that dark atom formation can account for the observed 511 keV line and outline the relevant parameter space.

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