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E. G. S. Luna

Publications and source records attributed to E. G. S. Luna.

At least 19 recordsLinked to original sources

Unitarity dressing of the dynamical gluon mass scale

We examine how $s$-channel unitarization changes the dynamical gluon mass scale $m_g$ inferred from high-energy elastic $pp$ scattering. The Born input is the Reggeized Landshoff--Nachtmann exchange of two nonperturbative gluons in a color-singlet state. We fit the ATLAS and TOTEM forward data separately, using eikonal and $U$-matrix unitarizations with logarithmic and power-law running masses derived from Schwinger--Dyson analyses. At the common reference cut $|t|_{\rm max}=0.12~\GeV^2$, the Born fits give $m_g=297$--$427~\MeV$; the eikonal and $U$-matrix fits give $265$--$360~\MeV$ and $243$--$328~\MeV$, respectively. Unitarization changes the fitted values of the intercept parameter $ε$, $m_g$, and the exponential slope $a_1$ of the proton form factor together. Over $0.10\leq |t|_{\rm max}\leq0.14~\GeV^2$, the $U$-matrix parameters vary less with the cut, while the eikonal fits to TOTEM show a pronounced drift. Replacing the infrared continuation of the logarithmic effective charge by a Curci--Ferrari prescription changes $m_g$ by a mean absolute relative shift of $1.77\%$ over twenty comparisons, with a maximum of $2.17\%$. The inferred scale remains in the few-hundred-MeV region, but its fitted value depends on the nonperturbative input and on the unitarization prescription.

hep-ph↗

Odderon in the diffractive dip region

We examine possible $C$-odd effects in elastic proton-proton and proton-antiproton scattering in the diffractive dip region. Collider data with $\sqrt{s}>500$ GeV are fitted for $0.2<|t|<1~\GeV^2$, using a simple Regge-inspired parametrization of effective $C$-even and $C$-odd amplitudes. The relative phases are not left free, but are fixed by the signature factors of the corresponding even and odd contributions. In this way, the real and imaginary parts of each term are linked by crossing. The $C$-even amplitude is first described by three effective Pomeron-like terms. The $C$-odd sector is then tested with several one-term Odderon-like forms. We find that the fits do not require a stable nonzero $C$-odd term: the odd contribution is either compatible with zero or becomes weakly constrained when we allow extra freedom. We then test whether the conclusion is changed by adding either a fourth Pomeron-like term or a second Odderon-like term. The improvement obtained with the fourth Pomeron-like term is mainly $C$-even, while the second Odderon-like term is not resolved as an independent contribution. These results provide a complementary test of recent determinations of the Odderon amplitude based on scaling and analyticity.

hep-ph↗

Unitarization Schemes for High-Energy Elastic Scattering

We examine key features of the eikonal and $U$-matrix unitarization schemes and apply both frameworks to investigate the high-energy behavior of the elastic scattering amplitude, considering input amplitudes whose asymptotic behavior is driven exclusively by Pomeron exchange. Particular attention is devoted to assessing how the extracted Pomeron parameters depend on the assumed trajectory form. In this context, we compare linear and nonlinear Pomeron trajectories, evaluating their impact on the phenomenological description of the data and on the stability of the fitted parameters.

hep-ph↗

Central multiplicity distributions in the multi-channel eikonal model

The multiplicity distribution of charged particles produced in the central rapidity region ($|η|<2.5$) is calculated within the multi-channel eikonal model using the AGK cutting rules and compared with ATLAS data at $\sqrt{s}=7$ and 13 TeV. The effects of color reconnection and/or string percolation are discussed.

hep-ph↗

Semihard interactions at TeV energies

We investigate the high-energy behavior of the total cross section, $σ_{\text{tot}}$, and the ratio of the real to imaginary parts of the scattering amplitude, $ρ$, in both proton-proton and antiproton-proton channels. Our analysis is based on a QCD-inspired model in which the rise of the cross sections is predominantly driven by semihard processes involving gluons. We address the tension between measurements from the ATLAS/ALFA and TOTEM Collaborations, showing that independent analyses of their datasets can provide statistically consistent descriptions of the overall data, even though they do not fully reproduce the central values of the $ρ$ parameter at $\sqrt{s} = 13$ TeV. The slight discrepancy between these central values and the model's predicted values, obtained using an asymptotic dominant crossing-even elastic scattering amplitude, points to the potential presence of an odd component in the semihard amplitude at high energies.

hep-ph↗

Semihard interactions at high energies

We revisit a minijet model to examine the behavior of the total cross section, $σ_{tot}$, and the ratio of the real to imaginary parts of the scattering amplitude, $ρ$, at high energies. In this framework, the growth of $σ_{tot}$ in $pp$ and $\bar{p}p$ channels is driven by semihard partonic processes dominated by gluon interactions. The QCD contribution to $σ_{tot}$ for the jet production is computed in the next-to-leading order. We analyze data separately from the TOTEM and ATLAS/ALFA Collaborations and find evidence in both cases suggesting the necessity of an odd semihard component that becomes asymptotically significant at high energies.

hep-ph↗

Odderon in the light of collider low-$t$ data

Odderon is the $C$-odd amplitude that does not fall (or decrease very slowly) with energy. The expected amplitude is small and mainly real. Therefore, extracting it from the data on top of a much larger $C$-even contribution is challenging. The only chance is to consider the very low $|t|$ region of Coulomb nuclear interference or the diffractive dip region. Here we perform the analysis of elastic scattering $pp$ and $\bar pp$ data at low momentum transfer $|t| < 0.1$ GeV$^2$ within large collider energy interval $\sqrt s = 50$ GeV $-$ 13 TeV in order to evaluate quantitatively the possible Odderon contribution. We use the two-channel eikonal model, which naturally accounts for the screening of the Odderon amplitude by the $C$-even (Pomeron) exchanges.

hep-ph↗

Unitarity effects in high-energy elastic scattering

We investigate the high-energy behavior of the elastic scattering amplitude using the eikonal and $U$-matrix unitarization schemes. This work extends the analysis in [1] by exploring the sensitivity of the Pomeron and Odderon parameters to the inclusion of differential cross-section data over an extended range of $|t|$.

hep-ph↗

Unitarity effects in elastic scattering at the LHC

We study the high-energy behavior of the elastic scattering amplitude using two distinct unitarization schemes: the eikonal and the $U$-matrix. Our analysis begins with a formalism involving solely Pomerons, incorporating pion-loop insertions in the Pomeron trajectory representing the nearest singularity generated by $t$-channel unitarity. Subsequently, we explore a scenario that includes the presence of an Odderon. In our analyses, we explore the tension between the TOTEM and the ATLAS measurements for $σ_{tot}$ and $dσ/dt$ at 7, 8, and 13 TeV, and the subsequent implications for the properties of both the Pomeron and Odderon. Our results show that the Odderon phase factor $ξ_{\Bbb O}= -1$ is favored in both unitarization schemes, supporting an Odderon with a phase opposite to that of other crossing-odd components of the scattering amplitude. More interestingly, this specific phase factor stands as the sole one that aligns with results consistent with a non-zero Odderon coupling.

hep-ph↗

Odderon contribution in light of the LHC low-$t$ data

We perform the analysis of elastic scattering $pp$ and $\bar{p}p$ data at low momentum transfer $|t|<0.1$ GeV$^2$ within large collider energy interval $\sqrt{s}=50$ GeV - 13 TeV in order to evaluate quantitatively the possible Odderon contribution. We use the two-channel eikonal model, which naturally accounts for the screening of the Odderon amplitude by $C$-even (Pomeron) exchanges.

hep-ph↗

Nonperturbative gluon exchange in $pp$ elastic scattering at TeV energies

We investigate the two-gluon-exchange model of the Pomeron using nonperturbative gluon propagators characterized by a dynamical mass scale. We present the results for an analysis of the available $pp$ differential cross section data at TeV energies which accounts for dynamical gluon masses obtained from a non-linear version of the Schwinger-Dyson equations. We show that our two-gluon exchange model gives a very good description of the LHC data, provided we demand the Reggeization of the scattering amplitude and make a suitable choice for the convolution of proton wave functions.

hep-ph↗

Soft Pomeron in light of the LHC correlated data

The LHC has released precise measurements of elastic proton-proton scattering that provide a unique constraint on the asymptotic behavior of the scattering amplitude at high energies. Recent reanalyses of part of these data indicate that the central values of some forward quantities would be different than initially observed. We introduce correlation information between the original and the reanalyzed data sets in a way suitable for a global fitting analysis of all data. The careful treatment of correlated errors leads to much less stringent limits on the $ρ$ uncertainty and sets up the stage for describing the forward data using a scattering amplitude dominated by only crossing-even terms. In the light of these correlated data we determine the parameters of the soft Pomeron from the Regge theory. We use Born-level and eikonalized amplitudes. In the Born-level case we estimate the contribution of the double Pomeron exchange, while in the latter case we investigate the role of the eikonalization in both the one- and two-channel models. The role of the proton-Pomeron vertex form and of the nearest $t$-channel singularity in the Pomeron trajectory receives particular attention. We discuss the implications of our results and present predictions for the total cross section and the $ρ$ parameter in proton-proton collisions at LHC and cosmic ray energies.

hep-ph↗

Matter-antimatter asymmetry and non-inertial effects

We investigate non-inertial effects on $CP$-violating processes using a model, based on the framework of quantum field theory in curved spacetimes, devised to account for the decay of accelerated particles. We show that the $CP$ violation parameter for the decay of accelerated kaons into two pions decreases very slightly as very high accelerations are achieved, implying decreased asymmetry between matter and antimatter in this regime. We discuss the relationship between these results and cosmological processes surrounding matter-antimatter asymmetry and argue that, due to the connection between non-inertial and thermal phenomena established by the Unruh effect, this kind of computation may prove useful in furthering the understanding of thermodynamical effects in curved spacetimes.

gr-qc↗

Non-inertial effects on CP-violating systems

An analysis of accelerated kaon decays based on the Unruh effect shows a slight decrease in a CP-violation parameter for very high accelerations, as a consequence of the previously know increase in decay rates for non-inertial systems. Its consequences on the understanding of the relation between thermal and non-inertial phenomena are briefly discussed.

hep-ph↗

QCD effective charges and the structure function $F_{2}$ at small-$x$: Higher twist effects

We consider the effect of higher twist operators of the Wilson operator product expansion in the structure function $F_{2}(x,Q^{2})$ at small-$x$, taking into account QCD effective charges whose infrared behavior is constrained by a dynamical mass scale. The higher twist corrections are obtained from the renormalon formalism. Our analysis is performed within the conventional framework of next-to-leading order, with the factorization and renormalization scales chosen to be $Q^{2}$. The infrared properties of QCD are treated in the context of the generalized double-asymptotic-scaling approximation. We show that the corrections to $F_{2}$ associated with twist-four and twist-six are both necessary and sufficient for a good description of the deep infrared experimental data.

hep-ph↗

Exclusive production of pions and the pion distribution amplitude

Considering, as a limit case, an approximately flat pion distribution amplitude, which is determined from the hardest, in momentum space, solution of the Bethe-Salpeter equation for the pion wave function, we compute the pion transition form factor $F_{πγγ^{*}}(Q^{2})$ and the pion form factor $F_π(Q^2)$, taking into account the LO as well as NLO form of the hard coefficient function entering the leading-twist factorization formula. We also compute the exclusive photoproduction of pions pairs at high energies, $γγ\to π^{+}π^{-}$, where perturbative QCD can be used to compute the hard scattering matrix elements. We verify that the existent data for exclusive pion production can be reasonably described as a function of such flat distribution amplitude.

hep-ph↗

Forward elastic scattering: Dynamical gluon mass and semihard interactions

The role of low-$x$ parton dynamics in dictating the high-energy behavior of forward scattering observables at LHC energies is investigated using a QCD-based model with even-under-crossing amplitude dominance at high-energies. We explore the effects of different sets of pre- and post-LHC fine-tuned parton distributions on the forward quantities $σ_{tot}$ and $ρ$, from $pp$ and $\bar{p}p$ scattering in the interval 10 GeV - 13 TeV. We also investigate the role of the leading soft contribution, the low-energy cuttoff, and the energy dependence of the semihard form factor on these observables. We show that in all cases investigated the highly restrictive data on $ρ$ parameter at $\sqrt{s}=13$ TeV indicate that a crossing-odd component may play a crucial role in forward elastic scattering at the highest energies. In the Regge language an odd-under-crossing object is called Odderon.

hep-ph↗