arXiv subjects

Jeremiah Birrell

Publications and source records attributed to Jeremiah Birrell.

48 records · Page 3Linked to original sources

arXiv2015

Dynamical Emergence of the Universe into the False Vacuum

We study how the hot Universe evolves and acquires the prevailing vacuum state, demonstrating that in specific conditions which are believed to apply, the Universe becomes frozen into the state with the smallest value of Higgs vacuum field $v=\langle h\rangle$, even if this is not the state of lowest energy. This supports the false vacuum dark energy $Λ$-model. Under several likely hypotheses we determine the temperature in the evolution of the Universe at which two vacuua $v_1, v_2$ can swap between being true and false. We evaluate the dynamical surface pressure on domain walls between low and high mass vaccua due to the presence of matter and show that the low mass state remains the preferred vacuum of the Universe.

astro-ph.CO↗

arXiv2015

Proposal for Resonant Detection of Relic Massive Neutrinos

We present a novel method for detecting the relic neutrino background that takes advantage of structured quantum degeneracy to amplify the drag force from neutrinos scattering off a detector. Developing this idea, we present a characterization of the present day relic neutrino distribution in an arbitrary frame, including the influence of neutrino mass and neutrino reheating by $e^+e^-$ annihilation. We present explicitly the neutrino velocity and de Broglie wavelength distributions for the case of an Earthbound observer. Considering that relic neutrinos could exhibit quantum liquid features at the present day temperature and density, we discuss the impact of neutrino fluid correlations on the possibility of resonant detection.

hep-ph↗

arXiv2014

Relic Neutrino Freeze-out: Dependence on Natural Constants

Analysis of cosmic microwave background radiation fluctuations favors an effective number of neutrinos, $N_ν>3$. This motivates a reinvestigation of the neutrino freeze-out process. Here we characterize the dependence of $N_ν$ on the Standard Model (SM) parameters that govern neutrino freeze-out. We show that $N_ν$ depends on a combination $η$ of several natural constants characterizing the relative strength of weak interaction processes in the early Universe and on the Weinberg angle $\sin^2θ_W$. We determine numerically the dependence $N_ν(η,\sin^2θ_W)$ and discuss these results. The extensive numerical computations are made possible by two novel numerical procedures: a spectral method Boltzmann equation solver adapted to allow emerging chemical non-equilibrium, and a method to evaluate Boltzmann equation collision integrals that generates a smooth integrand.

nucl-th↗

arXiv2014

Quark-Gluon Plasma as the Possible Source of Cosmological Dark Radiation

The effective number of neutrinos, $N_{\text{eff}}$, obtained from CMB fluctuations accounts for all effectively massless degrees of freedom present in the Universe, including but not limited to the three known neutrinos. Using a lattice-QCD derived QGP equation of state, we constrain the observed range of $N_{\text{eff}}$ in terms of the the freeze-out of unknown degrees of freedom near to quark-gluon hadronization. We explore limits on the coupling of these particles, applying methods of kinetic theory. We present bounds on the coupling of such particles and discuss the implications of a connection between $N_{\text{eff}}$ and the QGP transformation for laboratory studies of QGP.

nucl-th↗

arXiv2014

Boltzmann Equation Solver Adapted to Emergent Chemical Non-equilibrium

We present a novel method to solve the spatially homogeneous and isotropic relativistic Boltzmann equation. We employ a basis set of orthogonal polynomials dynamically adapted to allow for emergence of chemical non-equilibrium. Two time dependent parameters characterize the set of orthogonal polynomials, the effective temperature $T(t)$ and phase space occupation factor $Υ(t)$. In this first paper we address (effectively) massless fermions and derive dynamical equations for $T(t)$ and $Υ(t)$ such that the zeroth order term of the basis alone captures the particle number density and energy density of each particle distribution. We validate our method and illustrate the reduced computational cost and the ability to easily represent final state chemical non-equilibrium by studying a model problem that is motivated by the physics of the neutrino freeze-out processes in the early Universe, where the essential physical characteristics include reheating from another disappearing particle component ($e^\pm$-annihilation).

math.NA↗

arXiv2014

Non-Equilibrium Aspects of Relic Neutrinos: From Freeze-out to the Present Day

In this dissertation, we study the evolution and properties of the relic (or cosmic) neutrino distribution from neutrino freeze-out at $T=O(1)$ MeV through the free-streaming era up to today, focusing on the deviation of the neutrino spectrum from equilibrium. In particular, we demonstrate the presence of chemical non-equilibrium that continues to the present day. The work naturally separates into two parts. The first focuses on aspects of the relic neutrinos that can be explored using conservation laws. The second part studies the neutrino distribution using the full general relativistic Boltzmann equation. Part one begins with an overview of the history of the Universe, from just prior to neutrino freeze-out up through the present day, placing the history of cosmic neutrino evolution in its proper context. Motivated by the Planck CMB measurements of the effective number of neutrinos, we derive those properties of neutrino freeze-out that depend only on conservation laws and are independent of the details of the scattering processes. Part one ends with a characterization of the present day neutrino spectrum as seen from Earth. The second part of this dissertation focuses on the properties of cosmic neutrinos that depend on the details of the neutrino reactions, as is necessary for modeling the non-thermal distortions from equilibrium and computing freeze-out temperatures. We detail a new spectral method for solving the Boltzmann equation, based on a dynamical basis of orthogonal polynomials, as well as an improved procedure for analytically simplifying the corresponding scattering integrals for subsequent numerical computation. We apply these novel solution methods to solve the Boltzmann equation through the neutrino freeze-out period and perform parametric studies of the dependence of neutrino freeze-out on standard model parameters.

nucl-th↗

arXiv2013

Relic neutrinos: Physically consistent treatment of effective number of neutrinos and neutrino mass

We perform a model independent study of the neutrino momentum distribution at freeze-out, treating the freeze-out temperature as a free parameter. Our results imply that measurement of neutrino reheating, as characterized by the measurement of the effective number of neutrinos $N_ν$, amounts to the determination of the neutrino kinetic freeze-out temperature within the context of the standard model of particle physics where the number of neutrino flavors is fixed and no other massless (fractional) particles arise. At temperatures on the order of the neutrino mass, we show how cosmic background neutrino properties i.e. energy density, pressure, particle density, are modified in a physically consistent way as a function of neutrino mass and $N_ν$.

astro-ph.CO↗

arXiv2013

Traveling Through the Universe: Back in Time to the Quark-Gluon Plasma Era

We survey the early history of the discovery of quark gluon plasma and the early history of the Universe, beginning with the present day and reaching deep into QGP and almost beyond. We introduce cosmological Universe dynamics and connect the different Universe epochs with one another. We describe some of the many remaining open questions that emerge.

nucl-th↗

arXiv2013

Fugacity and Reheating of Primordial Neutrinos

We clarify in a quantitative way the impact that distinct chemical $T_c$ and kinetic $T_k$ freeze-out temperatures have on the reduction of the neutrino fugacity $Υ_ν$ below equilibrium, i.e. $Υ_ν<1$, and the increase of the neutrino temperature $T_ν$ via partial reheating. We establish the connection between $Υ_ν$ and $T_k$ via the modified reheating relation $T_ν(Υ_ν)/T_γ$, where $T_γ$ is the temperature of the background radiation. Our results demonstrate that one must introduce the chemical nonequilibrium parameter, i.e., the fugacity, $Υ_ν$, as an additional standard cosmological model parameter in the evaluation of CMB fluctuations as its value allows measurement of $T_k$.

astro-ph.CO↗

arXiv2013

Compact Ultra Dense Matter Impactors

We study interactions of meteorlike compact ultradense objects (CUDO), having nuclear or greater density, with Earth and other rocky bodies in the Solar System as a possible source of information about novel forms of matter. We study the energy loss in CUDO puncture of the body and discuss differences between regular matter and CUDO impacts.

astro-ph.EP↗

arXiv2012

Possibility of Electroweak Phase Transition at Low Temperature

We study models of strong first order `low' temperature electroweak phase transition. To achieve this we propose a class of Higgs effective potential models which preserve the known features of the present day massive phase. However, the properties of the symmetry restored massless phase are modified in a way that for a large parameter domain we find a strong first order transition occurring at a temperature hundreds of times lower than previously considered possible.

hep-ph↗

arXiv2011

Transition from ergodic to explosive behavior in a family of stochastic differential equations

We study a family of quadratic stochastic differential equations in the plane, motivated by applications to turbulent transport of heavy particles. Using Lyapunov functions, we find a critical parameter value $α_{1}=α_{2}$ such that when $α_{2}>α_{1}$ the system is ergodic and when $α_{2}<α_{1}$ solutions are not defined for all times. Hörmander's hypoellipticity theorem and geometric control theory are also utilized.

math.PR↗