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R. Fiore

Publications and source records attributed to R. Fiore.

At least 37 records · Page 2Linked to original sources
arXiv2011

Heavy quark currents in ultra-high energy neutrino interactions

We discuss heavy quark contributions to the neutrino-nucleon total cross section at very high energies, well above the real top production threshold. The top-bottom weak current is found to generate strong left-right asymmetry of neutrino-nucleon interactions. We separate contributions of different helicity states and make use of the $\bkappa$-factorization to derive simple and practically useful formulas for the left-handed ($F_L$) and right-handed ($F_R$) components of the conventional structure function $2xF_3=F_L-F_R$ in terms of the integrated gluon density. We show that $F_L\gg F_R$ and, consequently, $xF_3\approx F_T$, where $F_T$ is the transverse structure function. The conventional structure function $F_2=F_S+F_T$ at $Q^2\ll m_t^2$ appears to be dominated by its scalar (also known as longitudinal) component $F_S$ and the hierarchy $F_S\gg F_L\gg F_R$ arises naturally. We evaluate the total neutrino-nucleon cross section at ultra-high energies within the color dipole BFKL formalism.

hep-ph↗
arXiv2011

Connection between complete and Moebius forms of gauge invariant operators

We study the connection between complete representations of gauge invariant operators and their Moebius representations acting in a limited space of functions. The possibility to restore the complete representations from Moebius forms in the coordinate space is proven and a method of restoration is worked out. The operators for transition from the standard BFKL kernel to the quasi-conformal one are found both in Moebius and total representations.

hep-th↗
arXiv2011

UHE Neutrinos: Fusing gluons within diffraction cone

Currently available estimates of the gluon-fusion effect in ultra-high energy neutrino-nucleon interactions as well as in DIS on protons suffer from uncertainty in defining the scattering profile function $Γ(b)$. Indeed, the area, $S$, in the impact parameter space populated with interacting gluons varies by a factor of $4 - 5$ from one analysis to another. To get rid of uncertainties we specify the dipole-nucleon partial-wave amplitude $Γ(b)$ which meets the restrictions imposed by both the total dipole-nucleon cross section and the small angle elastic scattering amplitude. The area $S$ becomes a well defined quantity proportional to the diffraction cone slope. We solve numerically the non-linear color dipole BFKL equation and evaluate the UHE neutrino-nucleon total cross section. Our finding is that the saturation is a rather weak effect, $\lsim 25%$, up to $E_ν\sim 10^{12}$ GeV.

hep-ph↗
arXiv2010

Exclusive J/Psi photo- and electroproduction in a dual model

Exclusive J/Ψphoto- and electroproduction is studied in the framework of the analytic S-matrix theory. The differential and integrated elastic cross sections are calculated using the Modified Dual Amplitude with Mandelstam Analyticity (M-DAMA) model. The model is applied to the description of the available experimantal data and proves to be valid in a wide region of the kinematical variables s, t, and Q^2. Our amplitude can be used also as a universal background parametrization for the extraction of tiny resonance signals.

hep-ph↗
arXiv2010

UHE neutrinos: higher twists, scales, saturation

It is shown that in the ultra-high energy neutrino interactions the higher twist corrections brought about by the non-conservation of the top-bottom current dramatically change the longitudinal structure function, $F_L$. To the Double Leading Log Approximation simple and numerically accurate formulas for $F_L$ and $σ^{νN}$ are derived.

hep-ph↗
arXiv2010

Current non-conservation effects in ultra-high energy neutrino interactions

The overall hardness scale of the ultra-high energy neutrino-nucleon interactions is usually estimated as $Q^2\sim m_W^2$. The effect of non-conservation of weak currents pushes this scale up to the top quark mass squared and changes dynamics of the scattering process. The Double Leading Log Approximation provides simple and numerically accurate formula for the top-bottom contribution to the total cross section $σ^{νN}$. Corresponding correction to $σ^{νN}$ appears to be numerically large. It is comparable with the leading contribution evaluated in the massless quark approximation.

hep-ph↗
arXiv2009

Predictions for high-energy pp and \bar pp scattering from a finite sum of gluon ladders

An eikonalized elastic proton-proton and proton-antiproton scattering amplitude F(s,t), calculated from QCD as a finite sum of gluon ladders, is compared with the existing experimental data on the total cross section and the ratio ρ(s,0)=Re F(s,0)/Im F(s,0) of the real part to the imaginary part of the forward amplitude. Predictions for the expected LHC energies are given.

hep-ph↗
arXiv2009

Matching of the low-x evolution kernels

We demonstrate that the ambiguity of the low-x evolution kernels in the next-to-leading order (NLO) permits one to match the Mobius form of the BFKL kernel and the kernel of the colour dipole model and to construct the Mobius invariant NLO BFKL kernel in N=4 supersymmetric Yang-Mills theory.

hep-ph↗
arXiv2009

Higher twist effects in charmed-strange $ν$DIS diffraction

The non-conservation of charmed-strange current in the neutrino deep inelastic scattering ($ν$DIS) strongly affects the longitudinal structure function, $F_L$, at small values of Bjorken $x$. The corresponding correction to $F_L$ is a higher twist effect enhanced at small-$x$ by the rapidly growing gluon density factor. As a result, the component of $F_L$ induced by the charmed-strange current prevails over the light-quark component and dominates $F_L=F_L^{cs}+F_L^{ud}$ at $x\lsim 0.01$ and $Q^2\sim m_c^2$. The color dipole analysis clarifies the physics behind the phenomenon and provides a quantitative estimate of the effect.

hep-ph↗
arXiv2009

Exclusive J/Psi electroproduction in a dual model

Exclusive J/Psi electroproduction is studied in the framework of the analytic S-matrix theory. The differential and integrated elastic cross sections are calculated using the Modified Dual Amplitude with Mandelstam Analyticity (M-DAMA) model. The model is applied to the description of the available experimantal data and proves to be valid in a wide region of the kinematical variables s, t and Q^2. Our amplitude can be used also as a universal background parametrization for the extraction of tiny resonance signals.

hep-ph↗
arXiv2009

The BFKL-Regge factorization and $F_2^b$, $F_2^c$, $F_L$ at HERA: physics implications of nodal properties of the BFKL eigenfunctions

The asymptotic freedom is known to split the leading-$\log$ BFKL pomeron into a series of isolated poles in the complex angular momentum plane. One of our earlier findings was that the subleading hard BFKL exchanges decouple from such experimentally important observables as small-$x$ charm, $F_2^c$, and the longitudinal, $F_L$, structure functions of the proton at moderately large $Q^2$. For instance, we predicted precocious BFKL asymptotics of $F_2^c(x,Q^2)$ with intercept of the rightmost BFKL pole $α_{\Pom}(0)-1=Δ_{\Pom}\approx 0.4$. On the other hand, the small-$x$ open beauty photo- and electro-production probes the vacuum exchange for much smaller color dipoles which entails significant subleading vacuum pole corrections to the small-$x$ behavior. In view of the accumulation of the experimental data on small-$x$ $F_{2}^{c}$, $F_{2}^{b}$ and $F_{L}$ we extend our early predictions to the kinematical domain covered by new HERA measurements. Our parameter-free results agree well with the determination of $F_2^c$, $F_L$ and published H1 results on $F_2^b$ but slightly overshoot the very recent (2008, preliminary) H1 results on $F_2^b$.

hep-ph↗
arXiv2009

Forward Physics at the LHC; Elastic Scattering

The following effects in the nearly forward ("soft") region of the LHC are proposed to be investigated: 1) At small |t| the fine structure of the cone (Pomeron) shouldbe scrutinized: a) a break of the cone near $t\approx - 0.1 ~ GeV$^2, due to the two-pion threshold, and required by t-channel unitarity, is expected, and b) possible small-period oscillations between $t=0$ and the dip region. 2) In measuring the elastic $pp$ scattering and total $pp$ cross section at the LHC, the experimentalists are urged to treat the total cross section $σ_t,$ the ratio $ρ$, the forward slope $B$ and the luminosity ${\cal L}$ as free arameters, and to publish model-independent results on ${dN/{dt}}.$ 3) Of extreme interest are the details of the expected diffraction minimum in the differential cross section. Its position, expected in the interval $0.4<-t<1$ GeV$^2$ at the level of about $10^{-2} {\rm mb} \cdot$ GeV$^{-2}÷10^{-1} {\rm mb}\cdot$ GeV$^{-2}$, cannot be predicted unambiguously, and its depth, i.e. the ratio of $dσ/dt$ at the minimum to that at the subsequent maximum (about $-t=5 $GeV$^2$, which is about 5 is of great importance. 4) The expected slow-down with increasing $|t|$ of the shrinkage of the second cone (beyond the dip-bump), together with the transition from an exponential to a power decrease in $-t$, will be indicative of the transition from "soft" to "hard" physics. Explicit models are proposed to help in quantifying this transition. 5) In a number of papers a limiting behavior, or saturation of the black disc limit (BDL) was predicted. This controversial phenomenon shows that the BDL may not be the ultimate limit.

hep-ph↗
arXiv2009

On the discrepancy of the low-x evolution kernels

It is shown that in the case of the forward scattering the most part of the difference between the Möbius form of the BFKL kernel and the BK kernel in the next-to-leading order (NLO) can be eliminated by the transformation related to the choice of the energy scale in the representation of scattering amplitudes. Change of the nonforward BFKL kernel under this transformation is derived as well. The functional identity of the forward BFKL kernel in the momentum and Möbius representations in the leading order (LO) is exhibited and its NLO validity in N=4 supersymmetric Yang-Mills theory is proved.

hep-ph↗
arXiv2008

Current non-conservation effects in $ν$DIS diffraction

In the neutrino DIS diffraction the charged current non-conservation gives rise to sizable corrections to the longitudinal structure function, $F_L$. These corrections is a higher twist effect enhanced at small-$x$ by the rapidly growing gluon density. The phenomenon manifests itself in abundant production of charm and strangeness by longitudinally polarized W bosons of moderate virtualities $Q^2\lsim m_c^2$.

hep-ph↗
arXiv2008

Charm of small $x$ neutrino DIS

Due to the weak current non-conservation the diffractive excitation of charm and strangeness dominates the longitudinal structure function $F_L(x,Q^2)$ of neutrino DIS at small Bjorken $x$. Based on the color dipole BFKL approach we report quantitative predictions for this effect in the kinematical range of the CCFR/NuTeV experiment. We comment on the relevance of our findings to experimental tests of PCAC.

hep-ph↗
arXiv2008

Full of charm neutrino DIS

The color dipole analysis of small-$(x, Q^2)$ neutrino DIS induced by the charmed-strange ($cs$) current reveals ordering of dipole sizes $m_c^{-2}<r^2<m_s^{-2}$ typical of the Double Leading Log Approximation (DLLA). The DLLA resummation leads to the $cs$ component of the longitudinal structure function $F_L$ rising to small $x$ much faster than its light quark component. Based on the color dipole BFKL approach we report quantitative predictions for this effect in the kinematical range of the CCFR/NuTeV experiment.

hep-ph↗