arXiv subjects

Jarah Evslin

Publications and source records attributed to Jarah Evslin.

At least 73 records · Page 4Linked to original sources

arXiv2020

Finite Derivation of the One-Loop Sine-Gordon Soliton Mass

Calculations of quantum corrections to soliton masses generally require both the vacuum sector and the soliton sector to be regularized. The finite part of the quantum correction depends on the assumed relation between these regulators when both are taken to infinity. Recently, in the case of quantum kinks, a manifestly finite prescription for the calculation of the quantum corrections has been proposed, which uses the kink creation operator to relate the two sectors. In this note, we test this new prescription by calculating the one-loop correction to the Sine-Gordon soliton mass, reproducing the well-known result which has been derived using integrability.

hep-th↗

arXiv2020

Wave Packets Losing Their Covariance

In neutrino physics, it is sometimes assumed that all wave packets must transform covariantly as Lorentz vectors. We show in a simple example that even if the initial conditions of a wave packet are covariant, then evolution in a relativistic interacting theory followed by a measurement of entangled particles can lead to a wave packet which is no longer covariant.

hep-ph↗

arXiv2020

Manifestly Finite Derivation of the Quantum Kink Mass

In 1974 Dashen, Hasslacher and Neveu calculated the leading quantum correction to the mass of the kink in the scalar $ϕ^4$ theory in 1+1 dimensions. The derivation relies on the identification of the perturbations about the kink as solutions of the Poschl-Teller (PT) theory. They regularize the theory by placing it in a periodic box, although the kink is not itself periodic. They also require an ad hoc identification of plane wave and PT states which is difficult to interpret in the decompactified limit. We rederive the mass using the kink operator to recast this problem in terms of the PT Hamiltonian which we explicitly diagonalize using its exact eigenstates. We normal order from the beginning, rendering our theory finite so that no compactification is necessary. In our final expression for the kink mass, the form of the PT potential disappears, suggesting that our mass formula applies to other quantum solitons.

hep-th↗

arXiv2020

Approximate Neutrino Oscillations in the Vacuum

It is well known that neutrino oscillations may damp due to decoherence caused by the separation of mass eigenstate wave packets or by a baseline uncertainty of order the oscillation wave length. In this note we show that if the particles created together with the neutrino are not measured and do not interact with the environment, then the first source of decoherence is not present. This demonstration uses the saddle point approximation and also assumes that the experiment lasts longer than a certain threshold. We independently derive this result using the external wave packet model and also using a model in which the fields responsible for neutrino production and detection are treated dynamically. Intuitively this result is a consequence of the fact that the neutrino emission time does not affect the final state and so amplitudes corresponding to distinct emission times must be added coherently. This fact also implies that oscillations resulting from mass eigenstates which are detected simultaneously arise from neutrinos which were not created simultaneously but are nonetheless coherent, realizing the neutrino oscillation paradigm of Kobach, Manohar and McGreevy.

hep-ph↗

arXiv2019

Ground States of the $ϕ^4$ Double-Well QFT

At second order in perturbation theory, we find the ground states of the $ϕ^4$ double-well quantum field theory in 1+1 dimensions. The operators which create these ground states from the free vacuum are constructed explicitly at this order, as is the operator which interpolates between the ground states. As a warm up we perform the analogous calculation in quantum mechanics, where the true ground state is unique but in perturbation theory there are also two ground states.

hep-th↗

arXiv2019

Squeezing the Free Scalar Ground State

Consider two free Hamiltonians for the same scalar field with two different masses. Wefind a squeeze operator which maps the ground state of one to the other. The operatoris described in both the Dirac and also the Schrodinger wavefunctional formalismsfor quantum field theory. We conjecture that this construction can be generalized toobtain operators which map between distinct topological sectors in the same theory.

hep-th↗

arXiv2019

Uncertainty in the Reactor Neutrino Spectrum and Mass Hierarchy Determination

One of the challenges that must be overcome in order to determine the neutrino mass hierarchy using reactor neutrinos is the theoretical uncertainty in the unoscillated reactor neutrino spectrum: this is one of the reasons why, recently, it was proposed to add a near detector to the JUNO experiment. A model-independent treatment of the spectrum uncertainty will be discussed, as well as the effect that it will have on the final result. Moreover, since the neutrino spectrum depends on the chemical composition of the fuel, the spectra at the near and far detectors will be different, because they will receive neutrinos from different cores. Taking into account the time evolution of the chemical composition of the fuel in the reactor core, it is possible to reconstruct the far detector spectrum from the near detector data. We will show that the method used to reconstruct the spectrum can affect sensitivity to the mass hierarchy, however if the near detector is large enough the difference will be negligible.

hep-ph↗

arXiv2019

Continuum Limit Matrix Elements for the Tonks-Girardeau Ground State

The Tonks-Girardeau model is a quantum mechanical model of N impenetrable bosons in 1+1 dimensions. A Vandermonde determinant provides the exact N-particle wave function of the ground state, or equivalently the matrix elements with respect to position eigenstates. We consider the large $N$ limit of these matrix elements. We present a binning prescription which calculates the leading terms of the matrix elements in a time which is independent of $N$, and so is suitable for this limit. In this sense, it allows one to solve for the ground state of a strongly coupled continuum quantum field theory in the field eigenstate basis. As examples, we calculate the matrix elements with respect to states with uniform density and also states consisting of two regions with distinct densities.

hep-th↗

arXiv2019

Entangled Neutrino States in a Toy Model QFT

It has been claimed that wave packets must be covariant and also that decohered neutrino oscillations are always revived during measurement. These conjectures are supported by general arguments which are not specific to the electroweak theory, and so if they are true for neutrinos they will also be true for simplified models. In this paper we produce such a simplified model in which the neutrino wave function, including its entanglement with the source particle and the environment, can be calculated explicitly in quantum field theory. It exhibits neutrino oscillation, which is reduced at late times by decoherence due to interactions of the source with the environment. One simple lesson from this model is that only the difference between the environmental interactions before and after neutrino emission can reduce the amplitude of neutrino oscillations. The model will be used to test the conjectures in a companion paper.

hep-ph↗

arXiv2018

Anchoring and Binning the Coordinate Bethe Ansatz

The Coordinate Bethe Ansatz (CBA) expresses, as a sum over permutations, the matrix element of an XXX Heisenberg spin chain Hamiltonian eigenstate with a state with fixed spins. These matrix elements comprise the wave functions of the Hamiltonian eigenstates. However, as the complexity of the sum grows rapidly with the length N of the spin chain, the exact wave function in the continuum limit is too cumbersome to be exploited. In this note we provide an approximation to the CBA whose complexity does not directly depend upon N. This consists of two steps. First, we add an anchor to the argument of the exponential in the CBA. The anchor is a permutation-dependent integral multiple of 2 pi. Once anchored, the distribution of these arguments simplifies, becoming approximately Gaussian. The wave function is given by the Fourier transform of this distribution and so the calculation of the wave function reduces to the calculation of the moments of the distribution. Second, we parametrize the permutation group as a map between integers and we bin these maps. The calculation of the moments then reduces to a combinatorial exercise on the partitioning into bins. As an example we consider the matrix element between the classical and quantum ground states.

hep-th↗

arXiv2018

The Compactified Principal Chiral Model's Mass Gap

If the space of minima of the effective potential of a weakly coupled 2d quantum field theory is not connected, then a mass gap will be nonpertubatively generated. As examples, we consider two sigma models compactified on a small circle with twisted boundary conditions. In the compactified SO(3) model the vacuum manifold consists of two points and the mass gap is nonperturbative. In the case of the compactified SU(2) principal chiral model the vacuum manifold is a single circle and the mass gap is perturbative.

hep-th↗

arXiv2018

Extracting nuclear form factors with coherent neutrino scattering

Coherent elastic neutrino-nucleus scattering (CEvNS) can be used to determine the neutron part of nuclear form factors, unlocking intrinsic properties of nuclear structure. In contrast with other such methods, CEvNS is free from both strong interaction effects and Coulomb distortions. We propose precision measurements of CEvNS with an upcoming accelerator facility and determine the corresponding requirements for such a neutrino detector. We find that most significant backgrounds come from fast neutrons, induced by cosmogenic muons or from the pion decays at rest in the target station. With ton-scale liquid noble gas detectors, we will not only achieve percent level precision in the measurement of neutron radii but also clarify contributions of higher-order moments to nuclear form factors.

physics.ins-det↗

arXiv2018

Spherical T-Duality and the spherical Fourier-Mukai transform

In earlier papers, we introduced spherical T-duality, which relates pairs of the form $(P,H)$ consisting of an oriented $S^3$-bundle $P\rightarrow M$ and a 7-cocycle $H$ on $P$ called the 7-flux. Intuitively, the spherical T-dual is another such pair $(\hat P, \hat H)$ and spherical T-duality exchanges the 7-flux with the Euler class, upon fixing the Pontryagin class and the second Stiefel-Whitney class. Unless $\mathrm{dim}(M)\leq 4$, not all pairs admit spherical T-duals and the spherical T-duals are not always unique. In this paper, we define a canonical Poincaré virtual line bundle $\mathcal{P}$ on $S^3 \times S^3$ (actually also for $S^n\times S^n$) and the spherical Fourier-Mukai transform, which implements a degree shifting isomorphism in K-theory on the trivial $S^3$-bundle. This is then used to prove that all spherical T-dualities induce natural degree-shifting isomorphisms between the 7-twisted K-theories of the pairs $(P,H)$ and $(\hat P, \hat H)$ when $\mathrm{dim}(M)\leq 4$, improving our earlier results.

hep-th↗

arXiv2018

Getting the Most Neutrinos out of IsoDAR

Several experimental collaborations worldwide intend to test sterile neutrino models by measuring the disappearance of antineutrinos produced via isotope decay at rest (IsoDAR). The most advanced of these proposals have very similar setups, in which a proton beam strikes a target yielding neutrons which are absorbed by a high isotopic purity 7Li converter, yielding 8Li whose resulting decay yields the antineutrinos. In this note, we use FLUKA and GEANT4 simulations to investigate three proposed modifications of this standard proposal. In the first, the 7Li is replaced with 7Li compounds including a deuterium moderator. In the second, a gap is placed between the target and the converter to reduce the neutron bounce-back. Finally, we consider cooling the converter with liquid nitrogen. We find that these modifications can increase the antineutrino yield by as much as 50 percent. The first also substantially reduces the quantity of high purity 7Li which is needed.

physics.ins-det↗

arXiv2018

Spiked Monopoles

We introduce the spiked monopole, which is a 't Hooft-Polyakov monopole with two charged scalar Higgs fields, of which one enjoys a quartic self-interaction. The free Higgs field behaves as in a BPS monopole, reducing the inter-monopole repulsion. The other Higgs has a spiked profile similar to a non-BPS monopole. Using the methods from numerical relativity recently adapted to the Yang-Mills-Higgs theory by Vachaspati, we simulate the interactions of such monopoles. During the long lifetime of these simulations the individual monopoles are stable. We find that they are always repulsive, with a small repulsion only when the interaction Higgs VEV is proportionately small. We briefly comment on implications for giant monopole dark matter models and on supermassive black hole seeding by the spikes.

hep-th↗

arXiv2017

The Price of Shifting the Hubble Constant

An anisotropic measurement of the baryon acoustic oscillation (BAO) feature fixes the product of the Hubble constant and the acoustic scale $H_0 r_d$. Therefore, regardless of the dark energy dynamics, to accommodate a higher value of $H_0$ one needs a lower $r_d$ and so necessarily a modification of early time cosmology. One must either reduce the age of the Universe at the drag epoch or else the speed of sound in the primordial plasma. The first can be achieved, for example, with dark radiation or very early dark energy, automatically preserving the angular size of the acoustic scale in the Cosmic Microwave Background (CMB) with no modifications to post-recombination dark energy. However it is known that the simplest such modifications fall afoul of CMB constraints at higher multipoles. As an example, we combine anisotropic BAO with geometric measurements from strong lensing time delays from H0LiCOW and megamasers from the Megamaser Cosmology Project to measure $r_d$, with and without the local distance ladder measurement of $H_0$. We find that the best fit value of $r_d$ is indeed quite insensitive to the dark energy model, and is also hardly affected by the inclusion of the local distance ladder data.

astro-ph.CO↗

arXiv2017

Quantifying Departures from Equilibrium with the Spherical Jeans Equation

Proper motions of collisionless pointlike objects in a spherically symmetric system, for example stars in a galaxy, can be used to test whether that system is in equilibrium, with no assumptions regarding isotropy. In particular, the fourth order spherical Jeans equation yields expressions for two observable quantities characterizing the departure from equilibrium, both of which can be expressed in terms of time derivatives of first and third moments of the velocities. As illustrations, we compute these quantities for tracer distributions drawn from an exact equilibrium configuration and also from near equilibrium configurations generated using the N-body code GALIC.

astro-ph.GA↗

arXiv2017

Production and decay of K-shell hollow krypton in collisions with 52 - 197 MeV/u bare xenon ions

X-ray spectra of K-shell hollow krypton atoms produced in single collisions with 52 - 197 MeV/u Xe54+ ions are measured in a heavy-ion storage ring equipped with an internal gas-jet target. Energy shifts of the Kα_1,2^s, Kα_1,2^(h,s), and K\b{eta}_1,3^s transitions are obtained. Thus, the average number of the spectator L-vacancies presented during the x-ray emission is deduced. From the relative intensities of the Kα_1,2^s and Kα_1,2^(h,s) transitions, the ratio of K-shell hollow krypton to singly K-shell ionized atoms is determined to be 14 - 24%. In the considered collisions, the K-vacancies are mainly created by the direct ionization which cannot be calculated within the perturbation descriptions. The experimental results are compared with a relativistic coupled channel calculation performed within the independent particle approximation.

physics.atom-ph↗