arXiv subjects

Iain Stewart

Publications and source records attributed to Iain Stewart.

7 recordsLinked to original sources

arXiv2025

Dihadron Fragmentation and the Confinement Transition in Energy Correlators

In this letter, we relate the factorization for $e^+e^- \to h_1 h_2 X$ to the factorization for energy-energy correlators in the collinear limit. This enables us to give a nonperturbative proof of factorization for the energy correlators, relate the energy correlator jet function to transverse-momentum-sensitive dihadron fragmentation functions, and provide a rigorous description of the confinement transition region.

hep-ph↗

arXiv2024

Nonperturbative Effects in Energy Correlators: From Characterizing Confinement Transition to Improving $\alpha_s$ Extraction

Energy correlators provide a powerful observable to study fragmentation dynamics in QCD. We demonstrate that the leading nonperturbative corrections for projected $N$-point energy correlators are described by the same universal parameter for any $N$, which has already been determined from other event shape fits. Including renormalon-free nonperturbative corrections substantially improves theoretical predictions of energy correlators, notably the transition into the confining region at small angles. Nonperturbative corrections are shown to have a significant impact on $\alpha_s$ extractions.

hep-ph↗

arXiv2023

Power Counting to Saturation

We present a description of saturation in small $x$ deep inelastic scattering from power counting in a top-down effective theory derived from QCD. A factorization formula isolates the universal physics of the nucleus at leading power in $x$. The onset of saturation is then understood as a breakdown in the expansion in an emergent power counting parameter, which is defined by the matrix element of a gauge invariant operator. We identify a new radiation mode, which enables us to extend previous literature by distinguishing the appearance of the saturation scale from the transition to non-linear evolution.

hep-ph↗

arXiv2023

Small-$x$ Factorization from Effective Field Theory

We derive a factorization theorem that allows for resummation of small-$x$ logarithms by exploiting Glauber operators in the soft collinear effective field theory. Our analysis is carried out for the hadronic tensor $W^{\mu\nu}$ in deep inelastic scattering, and leads to the definition of a new gauge invariant soft function $S^{\mu\nu}$ that describes quark and gluon emission in the central region. This soft function provides a new framework for extending resummed calculations for coefficient functions to higher logarithmic orders. Our factorization also defines impact factors by universal collinear functions that are process independent, for instance being identical in small-$x$ DIS and Drell-Yan.

hep-ph↗

arXiv2021

Unstable Throughput: When the Difficulty Algorithm Breaks

In Proof-of-Work blockchains, difficulty algorithms serve the crucial purpose of maintaining a stable transaction throughput by dynamically adjusting the block difficulty in response to the miners' constantly changing computational power. Blockchains that may experience severe hash rate fluctuations need difficulty algorithms that quickly adapt the mining difficulty. However, without careful design, the system could be gamed by miners using coin-hopping strategies to manipulate the block difficulty for profit. Such miner behavior results in an unreliable system due to the unstable processing of transactions. We provide an empirical analysis of how Bitcoin Cash's difficulty algorithm design leads to cyclicality in block solve times as a consequence of a positive feedback loop. In response, we mathematically derive a difficulty algorithm using a negative exponential filter which prohibits the formation of positive feedback and exhibits additional desirable properties, such as history agnosticism. We compare the described algorithm to that of Bitcoin Cash in a simulated mining environment and verify that the former would eliminate the severe oscillations in transaction throughput.

cs.CR↗

arXiv2007

An iterated search for influence from the future on the Large Hadron Collider

We analyse an iterated version of Nielsen and Ninomiya (N&N)'s proposed card game experiment to search for a specific type of backward causation on the running of the Large Hadron Collider (LHC) at CERN. We distinguish "endogenous" and "exogenous" potential causes of failure of LHC and we discover a curious "cross-talk" between their respective probabilities and occurrence timescales when N&N-style backward causation is in effect. Finally, we note a kind of "statistical cosmic censorship" preventing the influence from the future from showing up in a statistical analysis of the iterated runs.

hep-ph↗

arXiv1996

Order alpha_s^2 beta_0 Correction to the Charged Lepton Spectrum in b \to c \ell \barν_\ell decays

We compute the α_s^2β_0 part of the two-loop QCD corrections to the charged lepton spectrum in b \to c \ell \barν_\ell decays and find them to be about 50\% of the first order corrections at all lepton energies, except those close to the end point. Including these corrections we extract the central values \barΛ=0.33 GeV and λ_1=-0.17 GeV^2 for the HQET matrix elements and use them to determine the $\overline{\rm MS}$ b and c quark masses, and |V_{cb}|.

hep-ph↗