arXiv subjects

Henry Lamm

Publications and source records attributed to Henry Lamm.

72 records · Page 4Linked to original sources

arXiv2018

Finite Density $QED_{1+1}$ Near Lefschetz Thimbles

One strategy for reducing the sign problem in finite-density field theories is to deform the path integral contour from real to complex fields. If the deformed manifold is the appropriate combination of Lefschetz thimbles -- or somewhat close to them -- the sign problem is alleviated. Gauge theories lack a well-defined thimble decomposition, and therefore it is unclear how to carry out a generalized thimble method. In this paper we discuss some of the conceptual issues involved by applying this method to $QED_{1+1}$ at finite density, showing that the generalized thimble method yields correct results with less computational effort than standard methods.

hep-lat↗

arXiv2018

Simulation of Nonequilibrium Dynamics on a Quantum Computer

We present a hybrid quantum-classical algorithm for the time evolution of out-of-equilibrium thermal states. The method depends upon classically computing a sparse approximation to the density matrix, and then time-evolving each matrix element via the quantum computer. For this exploratory study, we investigate the time-dependent Heisenberg model with five spins on the Rigetti Forest quantum virtual machine and a one spin system on the Rigetti 8Q-Agave quantum processor.

quant-ph↗

arXiv2018

Finite-Density Monte Carlo Calculations on Sign-Optimized Manifolds

We present a general technique for addressing sign problems that arise in Monte Carlo simulations of field theories. This method deforms the domain of the path integral to a manifold in complex field space that maximizes the average sign (therefore reducing the sign problem) within a parameterized family of manifolds. We presents results for the $1+1$ dimensional Thirring model with Wilson fermions on lattice sizes up to $40\times 10$. This method reaches higher $μ$ then previous techniques while substantially decreasing the computational time required.

hep-lat↗

arXiv2017

Predicting and Discovering True Muonium

The recent observation of discrepancies in the muonic sector motivates searches for the yet undiscovered atom true muonium $(μ^+μ^-)$. To leverage potential experimental signals, precise theoretical calculations are required. I will present the on-going work to compute higher-order corrections to the hyperfine splitting and the Lamb shift. Further, possible detection in rare meson decay experiments like REDTOP and using true muonium production to constrain mesonic form factors will be discussed.

hep-ph↗

arXiv2017

Deep Learning Beyond Lefschetz Thimbles

The generalized thimble method to treat field theories with sign problems requires repeatedly solving the computationally-expensive holomorphic flow equations. We present a machine learning technique to bypass this problem. The central idea is to obtain a few field configurations via the flow equations to train a feed-forward neural network. The trained network defines a new manifold of integration which reduces the sign problem and can be rapidly sampled. We present results for the $1+1$ dimensional Thirring model with Wilson fermions on sizable lattices. In addition to the gain in speed, the parameterization of the integration manifold we use avoids the "trapping" of Monte Carlo chains which plagues large-flow calculations, a considerable shortcoming of the previous attempts.

hep-lat↗

arXiv2017

Discovering True Muonium in $K_L\rightarrow (μ^+μ^-) γ$

Theoretical and phenomenological predictions of $\mathcal{BR}(K_L\rightarrow (μ^+μ^-) γ)\sim7\times10^{-13}$ are presented for different model form factors $F_{K_Lγγ^*}(Q^2)$. These rates are comparable to existing and near-term rare $K_L$ decay searches at J-PARC and CERN, indicating a discovery of true muonium is possible. The model uncertainties are sufficiently small that detection of true muonium could discriminate between the form factor models. Further discussion of potential backgrounds is made.

hep-ph↗

arXiv2017

$P-$state Positronium for Precision Physics: an Ultrafine Splitting at $α^6$

An "ultrafine" splitting in positronium between the $L=1$ spin-singlet state and the spin-average of the spin-triplet states is shown to arise only at order $α^6$. The QED prediction for $n=2$ states is $Δ_{2,P}=(683/172800)mα^6=73.7(1.2)$ kHz. This represents the smallest leading-order QED splitting known. Current experimental efforts could observe this splitting, and its observation can constrain new ultralight interactions, such as axions or $Z'$.

physics.atom-ph↗

arXiv2017

Some radiative corrections to the hyperfine splitting of true muonium: two-photon-exchange contributions

We consider a set of radiative contributions from one-loop lepton vacuum polarization to the hyperfine splitting of true muonium. Improving previous results, we obtain values for the electron-loop coefficients and extract their leading dependence upon $β=m_μ/m_e$. The coefficients are $C^μ_{20,1{\rm VPCT}}=0.734931603β$, $C^μ_{20,1{\rm VPCA}}=0.551198702β$, and $C^μ_{20,1{\rm VPT}}=0.419149715β$. The mass-independent contribution from three one-loop vacuum polarization is $C_{40,{\rm VPX}}=\frac{1}{127575}\left(-5255-2016π^2+51840ζ(3)\right)$. Contributions from $τ$ up to $\mathcal{O}(m_μα^8)$ are calculated.

physics.atom-ph↗

arXiv2016

Applying Bayesian Inference to Galileon Solutions of the Muon Problem

We derive corrections to atomic energy levels from disformal couplings in Galileon theories. Through Bayesian inference, we constrain the cutoff radii and Galileon scale via these corrections. To connect different atomic systems, we assume the various cutoff radii related by a one-parameter family of solutions. This introduces a new parameter $α$ which is also constrained. In this model, we predict shifts to muonic helium of $δE_{He^3}=1.97^{+9.28}_{-1.87}$ meV and $δE_{He^4}=1.69^{+9.25}_{-1.61}$ meV as well as for true muonium, $δE_{TM}=0.06^{+0.46}_{-0.05}$ meV.

hep-ph↗

arXiv2016

Hadronic Vacuum Polarization in True Muonium

The leading-order hadronic vacuum polarization contribution to the hyperfine splitting of true muonium is reevaluated in two ways. The first considers a more complex pionic form factor and better estimates of the perturbative QCD contributions. The second, more accurate method directly integrates the Drell ratio $R(s)$ to obtain $C_{1,\rm hvp}=-0.0489(3)$. This corresponds to an energy shift in the hyperfine splitting of $ΔE^μ_{hfs,\rm hvp}=276196(51)$ MHz.

physics.atom-ph↗

arXiv2016

Hyperfine Splitting in True Muonium to $\mathcal{O}(m_μα^6)$: Two Photon Annihilation Contribution from Other Flavors

The two-photon-annihilation contribution to the true muonium hyperfine splitting arising from $e$ and $τ$ loops is obtained analytically at order $m_μα^6$. The contribution to the hyperfine splitting is $-2.031092873 m_μα^6/n^3π^2=-793.926988/n^3$ MHz. The contribution to the triplet true muonium decay rate has also been obtained and was found to be $9.825708266 m_μα^6/n^3π^2=3840.737698/n^3$ MHz. Additional results have been computed for other purely leptonic bound states.

physics.atom-ph↗

arXiv2016

High Resolution Nonperturbative Light-Front Simulations of the True Muonium Atom

Through the development of a parallel code called TMSWIFT, an extensive light-front quantization study of the nonperturbative spectrum of the bound state $(μ^+μ^-)$, true muonium, has been performed. Using Padé approximants, it has been possible to extract continuum and infinite-cutoff limits for the singlet and triplet states for a range of values of the coupling constant $α$. This data set allows for an investigation of the $α$ dependence of the light-front spectra, the results of which are compared to standard calculations. Decay constants have also been obtained. Improved calculations have been undertaken for the energy shifts due to the presence of a second, lighter flavor ($e$). Finally, initial results for three-flavor ($e$, $μ$, $τ$) calculations are presented.

hep-ph↗

arXiv2016

Nonperturbative True Muonium on the Light Front with TMSWIFT

The true muonium $(μ\barμ)$ bound state presents an interesting test of light-cone quantization techniques. In addition to exhibiting the standard problems of handling non-perturbative calculations, true muonium requires correct treatment of $e\bar{e}$ Fock-state contributions. Having previously produced a crude model of true muonium using the method of iterated resolvents, our current work has focused on the inclusion of the box diagrams to improve the cutoff-dependent issues of the model. Further, a parallel computer code, TMSWIFT, allowing for smaller numerical uncertainties, has been developed. This work focuses on the current state of these efforts to develop a model of true muonium that is testable at near-term experiments.

hep-ph↗

arXiv2015

True muonium: the atom that has it all

Fundamental physics could be described as having a muon problem. Discrepancies between theory and experiment in a number of muonic measurements ($r_P$, $a_μ$, $H\rightarrowμτ$, $\mathcal{R}_K$, $\mathcal{R}_{D^*}$) have been observed in the last decade that demand explanation. True muonium, the bound state of a muon and its antiparticle, has the potential to put strong constraints on any beyond standard model physics that affects the muon sector. To study these effects, theoretical predictions and experiment need a, not unreasonable, precision of 100 MHz. Surprisingly, at this level, QCD and electroweak corrections become relevant in true muonium as well. Presented here is a discussion of the novel properties of true muonium from the standard model, potential discovery methods at near future facilities like DIRAC and HPS, and its ability to discriminate between a variety of solutions to the muon problem.

hep-ph↗

arXiv2015

Can Galileons solve the muon problem?

The leptonic bound states positronium and muonium are used to constrain galileon contributions to the Lamb shift of muonic hydrogen. Through the application of a variety of bounds on lepton compositeness, it is shown that either the assumption of equating the charge radius of a particle with its galileon scale radius is incompatible with experiments or the scale of galileons must be $M>1.33$ GeV, too large to solve the muon problem. The possibility of stronger constraints in the future from true muonium are discussed.

hep-ph↗

arXiv2015

Electroweak Corrections to the True Muonium Hyperfine Splitting

In contrast to other atomic systems, in true muonium ($μ^+μ^-$) the leading-order $Z$ boson corrections to the hyperfine splitting are shown to be experimentally accessible in the near future. This contribution ($-109$ MHz) constitutes a necessary contribution to a full $\mathcal{O}(mα^7)$ calculation of the true muonium hyperfine splitting. This would enable a number of solutions to the muon problem to be constrained. Additionally, we compute the general expression for a pseudovector coupling to particle-antiparticle bound states at leading order, including the annihilation channel.

hep-ph↗

arXiv2014

True Muonium $(μ^+ μ^-)$ on the Light Front

Applying Discretized Light Cone Quantization, we perform the first calculation of the spectrum of true muonium, the $μ^+ μ^-$ atom, as modified by the inclusion of an $|e\bar e >$ Fock component. The shift in the mass eigenvalue is found to be largest for triplet states. If $m_e$ is taken to be a substantial fraction of $m_μ$, the integrated probability of the electronic component of the $1 \, {}^3 /! S_1$ state is found to be as large as $O(10^{-2})$. Initial studies of the Lamb shift for the atom are performed. Directions for making the simulations fully realistic are discussed.

hep-ph↗

arXiv2013

Numerical Exploration of Soliton Creation

We explore the classical production of solitons in the easy axis O(3) model in 1+1 dimensions, for a wide range of initial conditions that correspond to the scattering of small breathers. We characterize the fractal nature of the region in parameter space that leads to soliton production and find certain trends in the data. We identify a tension in the initial conditions required for soliton production - low velocity incoming breathers are more likely to produce solitons, while high velocity incoming breathers provide momentum to the final solitons and enable them to separate. We find new "counter-spinning" initial conditions that can alleviate some of this tension.

hep-th↗