scholarly journals Two-loop gg → Hg amplitude mediated by a nearly massless quark

2016 ◽  
Vol 2016 (11) ◽  
Author(s):  
Kirill Melnikov ◽  
Lorenzo Tancredi ◽  
Christopher Wever
Keyword(s):  
Massless Quark

scholarly journals Updates on the QCD phase diagram from lattice

2021 ◽  
Vol 31 (1) ◽  
Author(s):  
Sayantan Sharma
Keyword(s):  
Phase Diagram ◽  
Lattice Gauge Theory ◽  
Topological Properties ◽  
Chiral Phase ◽  
Qcd Phase Diagram ◽  
Qcd Vacuum ◽  
Lattice Gauge ◽  
Massless Quark ◽  
Quark Flavors

AbstractDifferent aspects of the phase diagram of strongly interacting matter described by quantum chromodynamics (QCD), which have emerged from the recent studies using lattice gauge theory techniques, are discussed. A special emphasis is given on understanding the role of the anomalous axial U(1) symmetry in determining the order of the finite temperature chiral phase transition in QCD with two massless quark flavors and tracing its origin to the topological properties of the QCD vacuum.

scholarly journals Factorization at subleading power and endpoint divergences in h → γγ decay. Part II. Renormalization and scale evolution

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Ze Long Liu ◽  
Bianka Mecaj ◽  
Matthias Neubert ◽  
Xing Wang
Keyword(s):  
Decay Amplitude ◽  
Factorization Theorem ◽  
Effective Theory ◽  
Operator Matrix ◽  
Quark Loop ◽  
Perfect Agreement ◽  
Soft Collinear Effective Theory ◽  
Convolution Integrals ◽  
Factorization Formula ◽  
Massless Quark

Abstract Building on the recent derivation of a bare factorization theorem for the b-quark induced contribution to the h → γγ decay amplitude based on soft-collinear effective theory, we derive the first renormalized factorization theorem for a process described at subleading power in scale ratios, where λ = mb/Mh « 1 in our case. We prove two refactorization conditions for a matching coefficient and an operator matrix element in the endpoint region, where they exhibit singularities giving rise to divergent convolution integrals. The refactorization conditions ensure that the dependence of the decay amplitude on the rapidity regulator, which regularizes the endpoint singularities, cancels out to all orders of perturbation theory. We establish the renormalized form of the factorization formula, proving that extra contributions arising from the fact that “endpoint regularization” does not commute with renormalization can be absorbed, to all orders, by a redefinition of one of the matching coefficients. We derive the renormalization-group evolution equation satisfied by all quantities in the factorization formula and use them to predict the large logarithms of order $$ {\alpha \alpha}_s^2{L}^k $$ αα s 2 L k in the three-loop decay amplitude, where $$ L=\ln \left(-{M}_h^2/{m}_b^2\right) $$ L = ln − M h 2 / m b 2 and k = 6, 5, 4, 3. We find perfect agreement with existing numerical results for the amplitude and analytical results for the three-loop contributions involving a massless quark loop. On the other hand, we disagree with the results of previous attempts to predict the series of subleading logarithms $$ \sim {\alpha \alpha}_s^n{L}^{2n+1} $$ ∼ αα s n L 2 n + 1 .

scholarly journals Chiral symmetry breaking by monopole condensation

2017 ◽  
Vol 32 (23n24) ◽  
pp. 1750139 ◽  
Author(s):  
Aiichi Iwazaki
Keyword(s):  
Symmetry Breaking ◽  
Pair Production ◽  
Chiral Symmetry ◽  
Chiral Symmetry Breaking ◽  
Chiral Condensate ◽  
Low Energy ◽  
Chiral Anomaly ◽  
Symmetric Pair ◽  
Color Charge ◽  
Massless Quark

Under the assumption of Abelian dominance in QCD, we have shown that chiral condensate is locally present around each QCD monopole. The essence is that either charge or chirality of a quark is not conserved, when the low energy massless quark collides with QCD monopole. In reality, the charge is conserved so that the chirality is not conserved. Reviewing the presence of the local chiral condensate, we show by using chiral anomaly that chiral nonsymmetric quark pair production takes place when a color charge is putted in a vacuum with monopole condensation, while chiral symmetric pair production takes place in a vacuum with no monopole condensation. Our results strongly indicate that the chiral symmetry is broken by the monopole condensation.

scholarly journals Landau-Khalatnikov-Fradkin transformations for the two loop massless quark propagator

2021 ◽  
pp. 115606
Author(s):  
P. Dall'Olio ◽  
T. De Meerleer ◽  
D. Dudal ◽  
S.P. Sorella ◽  
A. Bashir
Keyword(s):  
Quark Propagator ◽  
Massless Quark

STRONG CP PROBLEM AND AN AXIAL U(1) GAUGE SYMMETRY

1993 ◽  
Vol 08 (32) ◽  
pp. 3049-3056
Author(s):  
PONG YOUL PAC ◽  
CHERL SOO PAHK
Keyword(s):  
Scalar Field ◽  
Gauge Symmetry ◽  
Standard Model ◽  
Degree Of Freedom ◽  
New Approach ◽  
The Standard Model ◽  
Massless Quark ◽  
Exact Term ◽  
Physical Degree

We extend the standard model by an axial U(1) gauge symmetry obtained from a rotation parametrized by a scalar field. In quantizing the system, the Peccei-Quinn symmetry is realized by introducing a BRST-exact term, which can provide a new approach to the strong CP problem without assuming a physical degree of freedom like the axion or the massless quark. We can find that the transition between different topological sectors of QCD via physical scattering processes is suppressed.

scholarly journals Two-loop QCD corrections to massless quark–gluon scattering

2001 ◽  
Vol 605 (1-3) ◽  
pp. 486-516 ◽  
Author(s):  
C. Anastasiou ◽  
E.W.N. Glover ◽  
C. Oleari ◽  
M.E. Tejeda-Yeomans
Keyword(s):  
Massless Quark

CLASSIFICATION OF SYMMETRY BREAKING PATTERNS IN HETEROTIC STRINGS ON Z3 ORBIFOLD

1990 ◽  
Vol 05 (08) ◽  
pp. 1529-1549 ◽  
Author(s):  
AKIRA FUJITSU ◽  
TETSURO KITAZOE ◽  
MASAYOSHI TABUSE ◽  
HARUHIKO NISHIMURA
Keyword(s):  
Symmetry Breaking ◽  
Mass Scale ◽  
Higgs Mechanism ◽  
Low Energy ◽  
Modular Invariance ◽  
Shift Vector ◽  
Heterotic Strings ◽  
Left Handed ◽  
Massless Quark

Symmetry breaking patterns of E8×E′8 on Z3 orbifold are completely analyzed for physically acceptable models by using a kind of Weyl transformation and modular invariance. It is shown that SU(3)×SU(2)×U(1)n cannot be obtained by using any kind of a shift vector and Wilson lines and that the minimal group including SU(3)×SU(2)×U(1) is SU(3)2×U(1)n which is realized by a shift vector and Wilson lines. All models accessible to realistic low energy theories are listed out and an example is described to get SU(3)×SU(2)×UY(1) by using Higgs mechanism with anomalous U(1) channel. The example is able to give massless quark, lepton and Higgs to suppress proton decay by Planck mass scale and to make left-handed neutrino massless.

scholarly journals Schrödinger versus Dirac equation for a massless quark

1982 ◽  
Vol 25 (5) ◽  
pp. 1443-1446 ◽  
Author(s):  
R. K. Bhaduri ◽  
M. Brack
Keyword(s):  
Dirac Equation ◽  
Massless Quark

scholarly journals Two-loop QCD helicity amplitudes for massless quark-massless gauge boson scattering

2003 ◽  
Vol 2003 (06) ◽  
pp. 033-033 ◽  
Author(s):  
E.W. Nigel Glover ◽  
Maria Elena Tejeda-Yeomans
Keyword(s):  
Gauge Boson ◽  
Helicity Amplitudes ◽  
Massless Quark

scholarly journals The two-loop perturbative correction to the (g − 2)μ HLbL at short distances

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Johan Bijnens ◽  
Nils Hermansson-Truedsson ◽  
Laetitia Laub ◽  
Antonio Rodríguez-Sánchez
Keyword(s):  
Electromagnetic Field ◽  
Perturbative Qcd ◽  
Operator Product Expansion ◽  
Short Distance ◽  
Operator Product ◽  
Quark Loop ◽  
Perturbative Correction ◽  
Massless Quark ◽  
Leading Term ◽  
Perturbative Corrections

Abstract The short-distance behaviour of the hadronic light-by-light (HLbL) contribution to (g − 2)μ has recently been studied by means of an operator product expansion in a background electromagnetic field. The leading term in this expansion has been shown to be given by the massless quark loop, and the non-perturbative corrections are numerically very suppressed. Here, we calculate the perturbative QCD correction to the massless quark loop. The correction is found to be fairly small compared to the quark loop as far as we study energy scales where the perturbative running for the QCD coupling is well-defined, i.e. for scales μ ≳ 1 GeV. This should allow to reduce the large systematic uncertainty associated to high-multiplicity hadronic states.

Sign in / Sign up

Export Citation Format

Share Document