scholarly journals Infrared divergences and the eikonal exponentiation

2021 ◽  
Vol 104 (4) ◽  
Author(s):  
Carlo Heissenberg
Keyword(s):  
Infrared Divergences

scholarly journals A critical look at the electroweak phase transition

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Andreas Ekstedt ◽  
Johan Löfgren
Keyword(s):  
Phase Transition ◽  
Generic Model ◽  
Electroweak Symmetry ◽  
Electroweak Phase Transition ◽  
Gauge Dependence ◽  
Perturbative Methods ◽  
The Standard Model ◽  
Gauge Fixing ◽  
Infrared Divergences ◽  
General Gauge

Abstract The electroweak phase transition broke the electroweak symmetry. Perturbative methods used to calculate observables related to this phase transition suffer from severe problems such as gauge dependence, infrared divergences, and a breakdown of perturbation theory. In this paper we develop robust perturbative tools for dealing with phase transitions. We argue that gauge and infrared problems are absent in a consistent power-counting. We calculate the finite temperature effective potential to two loops for general gauge-fixing parameters in a generic model. We demonstrate gauge invariance, and perform numerical calculations for the Standard Model in Fermi gauge.

scholarly journals Two-parton scattering amplitudes in the Regge limit to high loop orders

2020 ◽  
Vol 2020 (8) ◽  
Author(s):  
Simon Caron-Huot ◽  
Einan Gardi ◽  
Joscha Reichel ◽  
Leonardo Vernazza
Keyword(s):  
Scattering Amplitudes ◽  
Scattering Amplitude ◽  
Dimensional Regularization ◽  
High Energy ◽  
Logarithmic Order ◽  
Finite Radius ◽  
High Loop ◽  
Parton Scattering ◽  
Infrared Divergences ◽  
Regge Limit

Abstract We study two-to-two parton scattering amplitudes in the high-energy limit of perturbative QCD by iteratively solving the BFKL equation. This allows us to predict the imaginary part of the amplitude to leading-logarithmic order for arbitrary t-channel colour exchange. The corrections we compute correspond to ladder diagrams with any number of rungs formed between two Reggeized gluons. Our approach exploits a separation of the two-Reggeon wavefunction, performed directly in momentum space, between a soft region and a generic (hard) region. The former component of the wavefunction leads to infrared divergences in the amplitude and is therefore computed in dimensional regularization; the latter is computed directly in two transverse dimensions and is expressed in terms of single-valued harmonic polylogarithms of uniform weight. By combining the two we determine exactly both infrared-divergent and finite contributions to the two-to-two scattering amplitude order-by-order in perturbation theory. We study the result numerically to 13 loops and find that finite corrections to the amplitude have a finite radius of convergence which depends on the colour representation of the t-channel exchange.

scholarly journals Inflationary infrared divergences: geometry of the reheating surface vs. δNformalism

2010 ◽  
Vol 2010 (08) ◽  
pp. 006-006 ◽  
Author(s):  
C.T Byrnes ◽  
M Gerstenlauer ◽  
A Hebecker ◽  
S Nurmi ◽  
G Tasinato
Keyword(s):  
Infrared Divergences

scholarly journals Two-loop $$ \mathcal{O} $$((αt + αλ + ακ)2) corrections to the Higgs boson masses in the CP-violating NMSSM

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Thi Nhung Dao ◽  
Martin Gabelmann ◽  
Margarete Mühlleitner ◽  
Heidi Rzehak
Keyword(s):  
Higgs Boson ◽  
Higgs Mass ◽  
Goldstone Boson ◽  
Higgs Sector ◽  
Momentum Dependence ◽  
Loop Order ◽  
Fortran Code ◽  
Higher Order Corrections ◽  
Infrared Divergences ◽  
The Impact

Abstract We present our computation of the $$ \mathcal{O} $$ O ((αt + αλ + ακ)2) two-loop corrections to the Higgs boson masses of the CP-violating Next-to-Minimal Supersymmetric Standard Model (NMSSM) using the Feynman-diagrammatic approach in the gaugeless limit at vanishing external momentum. We choose a mixed $$ \overline{\mathrm{DR}} $$ DR ¯ -on-shell (OS) renormalisation scheme for the Higgs sector and apply both $$ \overline{\mathrm{DR}} $$ DR ¯ and OS renormalisation in the top/stop sector. For the treatment of the infrared divergences we apply and compare three different regularisation methods: the introduction of a regulator mass, the application of a small momentum expansion, and the inclusion of the full momentum dependence. Our new corrections have been implemented in the Fortran code NMSSMCALC that computes the Higgs mass spectrum of the CP-conserving and CP-violating NMSSM as well as the Higgs boson decays including the state-of-the-art higher-order corrections. Our numerical analysis shows that the newly computed corrections increase with rising λ and κ, remaining overall below about 3% compared to our previously computed $$ \mathcal{O} $$ O (αt(αt + αs)) corrections, in the region compatible with perturbativity below the GUT scale. The renormalisation scheme and scale dependence is of typical two-loop order. The impact of the CP-violating phases in the new corrections is small. We furthermore show that the Goldstone Boson Catastrophe due to the infrared divergences can be treated in a numerically efficient way by introducing a regulator mass that approximates the momentum-dependent results best for squared mass values in the permille range of the squared renormalisation scale. Our results mark another step forward in the program of increasing the precision in the NMSSM Higgs boson observables.

scholarly journals CP-violating transport theory for electroweak baryogenesis with thermal corrections

2021 ◽  
Vol 2021 (11) ◽  
pp. 042
Author(s):  
Kimmo Kainulainen
Keyword(s):  
Source Term ◽  
Transport Theory ◽  
Finite Width ◽  
Source Terms ◽  
Boltzmann Equations ◽  
Current Divergence ◽  
The One ◽  
Infrared Divergences ◽  
Correct Implementation ◽  
Divergence Equations

Abstract We derive CP-violating transport equations for fermions for electroweak baryogenesis from the CTP-formalism including thermal corrections at the one-loop level. We consider both the VEV-insertion approximation (VIA) and the semiclassical (SC) formalism. We show that the VIA-method is based on an assumption that leads to an ill-defined source term containing a pinch singularity, whose regularisation by thermal effects leads to ambiguities including spurious ultraviolet and infrared divergences. We then carefully review the derivation of the semiclassical formalism and extend it to include thermal corrections. We present the semiclassical Boltzmann equations for thermal WKB-quasiparticles with source terms up to the second order in gradients that contain both dispersive and finite width corrections. We also show that the SC-method reproduces the current divergence equations and that a correct implementation of the Fick's law captures the semiclassical source term even with conserved total current ∂μ j μ = 0. Our results show that the VIA-source term is not just ambiguous, but that it does not exist. Finally, we show that the collisional source terms reported earlier in the semiclassical literature are also spurious, and vanish in a consistent calculation.

scholarly journals Infrared divergences and quantum coherence

2018 ◽  
Vol 78 (8) ◽  
Author(s):  
César Gómez ◽  
Raoul Letschka ◽  
Sebastian Zell
Keyword(s):  
Quantum Coherence ◽  
Infrared Divergences

scholarly journals Removing infrared divergences from two-loop integrals

2019 ◽  
Vol 2019 (7) ◽  
Author(s):  
Charalampos Anastasiou ◽  
George Sterman
Keyword(s):  
Infrared Divergences
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