Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · hep-ph/0502148

QCD at Low Energies

B. L. Ioffe
View original source ↗Read source document ↗Export metadata ↓

Abstract

The modern status of basic low energy QCD parameters is reviewed. It is demonstrated, that the recent data allows one to determine the light quark mass ratios with an accuracy 10-15%. The general analysis of vacuum condensates in QCD is presented, including those induced by external fields. The QCD coupling constant alpha_s is found from the tau-lepton hadronic decay rate. V-A spectral functions of tau-decay are used for construction of the V-A polarization operator Pi_{V-A}(s) in the complex s-plane. The operator product expansion (OPE) is used up to dimension D=10 and the sum rules along the rays in the complex s-plane are constructed. The best values of quark condensate and alpha_s<0|qq|0>^2 are found. The value of quark condensate is confirmed by considering the sum rules for baryon masses. Gluon condensate is found in four ways: by considering of V+A polarization operator based on the tau-decay data, by studying the sum rules for polarization operators momenta in charmonia in vector, pseudoscalar and axial channels. All of these determinations are in agreement and result in <(alpha_s/pi)G^2 > =0.005 \pm 0.004 GeV^4. Valence quark distributions in proton are calculated in QCD using the OPE in proton current virtuality. The quark distributions agree with those found from the deep inelastic scattering data. The same value of gluon condensate is favoured.

Explore related subjects

hep-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

B. L. Ioffe. 2005-04-28. QCD at Low Energies. https://doi.org/10.1016/j.ppnp.2005.05.001

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

QCD Axion Conversion in Magnetospheres of Neutron Stars

The axion-converted-photons flux plays a key role in searches of QCD axions as a dark matter (DM) candidate. In addition to solving the strong CP problem, these may explain the properties of the mysterious DM. Neutron star (NS) cooling by neutrino/axion emissions rate constrains the astrophysical properties of superdense matter. We attempt to analyse the impact of strong magnetic fields on the emission properties of axions by employing the APR, FPS, and SLY equation of State (EoS). We modify the Tolman Oppenheimer Volkoff (TOV) equations by considering effects of strong fields' and generate profiles. We assume Cooper-pair-breaking formation (PBF) and the Bremsstrahlung process occurring in the core of NS. We use the radial distance-dependent magnetic field configuration within the permissible limit of the central magnetic field. Our work explores the variations in the axion masses of 10 meV, 15 meV, and 20 meV as a cooling source for spherically symmetric magnetised NSs. We have also shown the energy spectrum of axions and their conversion to photons. Our analysis shows that the cooling rate and the luminosity of observables (axions) for NSs change significantly due to the magnetic field. The results for the luminosity of axions is quite sensitive to its mass and EoS, as the less separation is observed for SLY EoS in comparison to the FPS and APR EoS. We report that the spectrum of axions from the Bremsstrahlung process dominates over the PBF process at lesser axion energies, within the possible axion mass range for PSR J1357-6429 NS. Our results reveal that the impact of the magnetic field is less at lower axion energies, indicating the necessity for including a magnetic field in axion-to-photon conversion mechanisms. The results for the axions mass 10 meV and 15 meV as compared to 20 meV confirms the existing report of the 16 meV.

hep-ph↗
arXiv2026

Search for Vector-Like Singlet Top ($T$) Quark in a Future Muon-Proton ($μp$) Collider at $\sqrt{s} = 5.29, 6.48,$ and $9.16$ TeV using Advanced Machine Learning Architectures

We study the sensitivity of a future $μp$ collider to singly produced singlet vector-like $T$ quarks in the $T\to Wb$ decay mode across both fully hadronic ($bjj$) and leptonic ($b\ellν$) final states at $\sqrt{s}=5.29$, $6.48$, and $9.16~\mathrm{TeV}$. Utilizing resolved-object reconstruction and TMVA-based multivariate classifiers (BDT, BDTG, MLP, and Likelihood), we perform a fast-simulation scan over $m_T=2$--$5~\mathrm{TeV}$ and the $(g^{*},m_T)$ parameter space. To quantify improvements, we compare this multivariate selection against the closest cut-based baseline at a benchmark point of $m_T=3~\mathrm{TeV}$, $\sqrt{s}=9.16~\mathrm{TeV}$, and $\mathcal{L}=3000~\mathrm{fb}^{-1}$, incorporating a $20\%$ background-normalization uncertainty via the Asimov significance $Z_A$. At this benchmark, the hadronic channel exhibits a substantial enhancement in both $S/\sqrt{S+B}$ and $Z_A$, improving from $18.05$ and $1.44$ to $273.51$ and $42.24$, respectively. Similarly, the leptonic channel improves from $3.51$ and $0.330$ to $113.85$ and $21.51$. In the full parameter scan, the $\sqrt{s}=9.16~\mathrm{TeV}$ configuration provides the strongest sensitivity at $\mathcal{L}=3000~\mathrm{fb}^{-1}$. The hadronic channel excludes (discovers) regions with $g^{*}\in[0.20,0.50]$ ($[0.30,0.50]$) up to $m_T\approx4.0~(3.5)~\mathrm{TeV}$, while the leptonic channel remains sensitive up to $m_T\approx5.0~\mathrm{TeV}$ for $g^{*}\in[0.10,0.50]$. These gains arise from the higher-purity multivariate signal regions evaluated under a common significance prescription, and not from a change of the collider configuration. The projections assume resolved-object reconstruction and fast detector simulation, and the absolute reach should be read with these assumptions in mind.

hep-ph↗
arXiv2026

Particle--antiparticle asymmetry from charge separation at expanding horizons

In a Friedmann universe with a time-varying cosmological term, massive particle--antiparticle pairs are produced continuously from the spacetime vacuum, and their members are separated by horizons. Along the cosmic history that explains $n_s$, $A_s$, $r$ and the low-$\ell$ power anomaly, we show how this separation generates the observed asymmetry. Horizons absorb the charge they separate, since gravity does not conserve global charges. Charge separation at the many horizons inside today's Hubble volume then acts as a volume violation of the U(1) charge, at a rate $Γ_C=κ_CΓ_M$ proportional to pair production. The sign requires a C- and CP-odd coupling to the time arrow. We describe both by an effective Lagrangian with a U(1)-violating coupling $g_c\,δ\mathcal O_SΦ^2$ to the spacetime vacuum and a time bias $-\partial_μf(R)\,J^μ$. For $f=c_a\ln|R|$ the chemical potential of producing a particle is $μ\simeq2c_a\dot H/H$. The asymmetry per pair reaches an attractor in the pair-dominated episode and freezes when the cosmological term is exhausted. The observed value requires $|c_a|/τ_S\simeq(0.65$--$1.0)\times10^{-4}$, with $T_S=τ_SH/2π$ the temperature of the spacetime vacuum, and its sign is fixed by the arrow of time. The Yukawa decays of the pairs transfer the asymmetry, with a uniform sign, to baryons and leptons and to dark-matter particles. The current of the charged decay products generates a magnetic field of $10^{-14}$--$10^{-11}$ G today on the coherence length of reheating.

hep-ph↗