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G. Pettini

Publications and source records attributed to G. Pettini.

At least 19 recordsLinked to original sources

Electrodynamic forces driving DNA-protein interactions at large distances

In the present paper we address the general problem of selective electrodynamic interactions between DNA and protein, which is motivated by decades of theoretical study and our very recent experimental findings (M. Lechelon et al, \textit{Sci Adv} \textbf{8,} eabl5855 (2022)). Inspired by the Davydov and Holstein-Fr\"{o}hlich models describing electron motion along biomolecules, and using a model Hamiltonian written in second quantization, the time-dependent variational principle (TDVP) is used to derive the dynamical equations of the system. We demonstrate the efficacy of this {second-quantized} model for a well-documented biochemical system consisting of a restriction enzyme, \textit{Eco}RI, which binds selectively to a palindromic six-base-pair target within a DNA oligonucleotide sequence to catalyze a DNA double-strand cleavage. The time-domain Fourier spectra of the electron currents numerically computed for the DNA fragment and for the \textit{Eco}RI enzyme, respectively, exhibit a cross-correlation spectrum with a sharp co-resonance peak. When the target DNA recognition sequence is randomized, this sharp co-resonance peak is replaced with a broad and noisy spectrum. Such a sequence-dependent charge transfer phenomenology is suggestive of a potentially rich variety of selective electrodynamic interactions influencing the coordinated activity of DNA substrates, enzymes, transcription factors, ligands, and other proteins under realistic biochemical conditions characterized by electron-phonon excitations.

physics.bio-ph

Particles with anomalous magnetic moment in external e.m. fields: the proper time formulation

In this paper we evaluate the expression for the Green function of a pseudo-classical spinning particle interacting with constant electromagnetic external fields by taking into account the anomalous magnetic and electric moments of the particle. The spin degrees of freedom are described in terms of Grassmann variables and the evolution operator is obtained through the Fock-Schwinger proper time method.

hep-th

Foldy-Wouthuysen Transformation for a Spinning Particle with Anomalous Magnetic Moment

We study the Foldy-Wouthuysen transformation for a pseudoclassical particle with anomalous magnetic moment in an external, stationary electromagnetic field. We show that the transformation can be expressed in a closed form for neutral particles in purely electrostatic fields and for neutral and charged particles in external magnetostatic fields. The explicit expressions of the diagonalized Hamiltonians are calculated.

hep-th

A NJL-based study of the QCD critical line

We employ a 3 flavor NJL model to stress some general remarks about the QCD critical line. The dependence of the critical curve on $μ_q=(μ_u+μ_d)/2$ and $μ_I=(μ_u-μ_d)/2$ is discussed. The quark masses are varied to confirm that, in agreement with universality arguments, the order of transition depends on the number of active flavors $N_f$. The slope of the critical curve vs. chemical potential is studied as a function of $N_f$. We compare our results with those recently obtained in lattice simulations to establish a comparison among different models.

hep-ph

Pion and kaon condensation in a 3-flavor NJL model

We analyze the phase diagram of a three-flavor Nambu-Jona-Lasinio model at finite temperature $T$ and chemical potentials $μ_u, μ_d, μ_s$. We study the competition of pion and kaon condensation and we propose a physical situation in which kaon condensation could be led only by light quark finite densities.

hep-ph

Ladder-QCD at finite isospin chemical potential

We use an effective QCD model (ladder-QCD) to explore the phase diagram for chiral symmetry breaking and restoration at finite temperature with different $u,d$ quark chemical potentials. In agreement with a recent investigation based on the Nambu-Jona-Lasinio model, we find that a finite pion condensate shows up for high enough isospin chemical potential $μ_{I}=(μ_{u}-μ_{d})/2$. For small $μ_{I}$ the phase diagram in the $(μ_B,T)$ plane shows two first order transition lines and two critical ending points.

hep-ph

Strange quark production in a statistical effective model

An effective model with constituent quarks as fundamental degrees of freedom is used to predict the relative strangeness production pattern in both high energy elementary and heavy ion collisions. The basic picture is that of the statistical hadronization model, with hadronizing color-singlet clusters assumed to be at full chemical equilibrium at constituent quark level. Thus, by assuming that at least the ratio between strange and non-strange constituent quarks survives in the final hadrons, the apparent undersaturation of strange particle phase space observed in the data can be accounted for. In this framework, the enhancement of relative strangeness production in heavy ion collisions in comparison with elementary collisions is mainly owing to the excess of initial non-strange matter over antimatter and the so-called canonical suppression, namely the constraint of exact color and flavor conservation over small volumes.

hep-ph

Strangeness production in a constituent quark model

We develop a model to calculate strangeness production in both elementary and heavy ion collisions, within the framework of a statistical approach to hadronisation. Calculations are based on the canonical partition function of the thermal Nambu-Jona-Lasinio model with exact conservation of flavor and color. It turns out that the growth of strange quarks production in heavy ion collisions is due to the initial excess of non-strange matter over antimatter, whereas a suppression occurs for elementary collisions, owing to the constraint of exact quantum charges conservation over small volumes.

hep-ph

Strangeness production in a statistical effective model of hadronisation

We suppose that overall strangeness production in both high energy elementary and heavy ion collisions can be described within the framework of an equilibrium statistical model in which the effective degrees of freedom are constituent quarks as used in effective lagrangian models. In this picture, the excess of relative strangeness production in heavy ion collisions with respect to elementary particle collisions arises from the unbalance between initial non-strange matter and antimatter and from the exact colour and flavour quantum number conservation over different finite volumes. The comparison with the data and the possible sources of model dependence are discussed.

hep-ph

Chiral Meson Masses at Finite Temperature and Density

The ratio of the sigma mass to the pion mass at finite temperatures and densities provides for a quantitative signal of chiral symmetry breaking. We calculate this ratio by using an extension to finite chemical potential of the field theoretic composite operator formalism as applied to QCD. The calculation is limited to regions of the phase diagram where only quark-antiquark condensates dominate (no quark-quark condensates) and it confirms the expected behaviours. In particular the sigma becomes an essentially stable particle in a narrow region bordering the transition line from broken to restored chirality . This pattern is qualitatively the same both for the region where the transition is of second order as for the region where it is of first order (apart from the discontinuities expected in the latter case).

hep-ph

Pseudoscalar and scalar meson masses at finite temperature

The composite operator formalism is applied to QCD at finite temperature to calculate the masses of scalar and pseudoscalar mesons. In particular the ratio of the sigma mass to the pion mass is an interesting measure of the degree of chiral symmetry breaking at different temperatures. We calculate the temperature T* at which M_sigma(T) < 2M_pi(T), above which the sigma partial width into two pions vanishes. We find T*=0.95T_c (where T_c is the critical temperature for the chiral phase transition), within the full effective potential given by the formalism. We find that an expansion a-la Landau of the effective potential around the critical point in the limit of small quark mass provides for a very good determination of T*.

hep-ph

Equation of state for the 2+1 dimensional Gross-Neveu model at order 1/N

We calculate the equation of state of the Gross-Neveu model in 2+1 dimensions at order 1/N, where N is the number of fermion species. We make use of a general formula valid for four-fermion theories, previously applied to the model in 1+1 dimensions. We consider both the discrete and continuous symmetry versions of the model. We show that the pion-like excitations give the dominant contribution at low temperatures. The range of validity for such pion dominance is analyzed. The complete analysis from low to high temperatures also shows that in the critical region the role of composite states is relevant, even for quite large N, and that the free-component behaviour at high T starts at about twice the mean field critical temperature.

hep-ph

Corrections to the Pagels-Stokar Formula for f_π

Within the composite operator formalism we derive a formula for the pion decay constant $f_π$, as defined directly from the residue at the pion pole of the meson propagator, rather than from the matrix element of the axial current. The calculation is performed under some simplifying assumptions, and we verify the complete consistency with soft-pion results, in particular with the Adler-Dashen relation. The formula one obtains for (the pole-defined) $f_π^2$ differs from the previous Pagels-Stokar expression by an additive term, and it still provides $f_π^2$ in terms of the quark self-energy. We make some numerical estimates leading to $(30 ÷40)%$ deviation for $f_π^2$ with respect to the Pagels-Stokar formula.

hep-ph

Low Temperature Dominance of Pion-like Excitations in the Massive Gross-Neveu Model at Order 1/N

We perform a 1/N-expansion of the partition function of the massive Gross-Neveu model in 1+1 dimensions. The procedure allows for the inclusion of the contribution of scalar and pseudoscalar composites (of order 1/N) to the equation of state. The naive expectation that the bosonic fluctuations correct significantly the mean field approximation at low temperatures is confirmed by our calculations. Actually the relevant degrees of freedom of hadronic matter at low temperatures are found to be pion-like excitations, rather than the fundamental constituents.

hep-ph

1/N_c expansion for the partition function in four fermion models

We present a derivation of the bosonic contribution to the thermodynamical potential of four fermion models by means of a $1/N_c$-expansion of the functional integral defining the partition function. This expansion turns out to be particularly useful to correct the mean field approximation expecially at low temperatures, where the relevant degrees of freedom are low-mass bosonic excitations (pseudogoldstones).

hep-ph

Disoriented Chiral Condensates: A Dynamical Simulation in the (2+1)-Dimensional Gross-Neveu Model

We simulate the formation and growth of disoriented chiral condensate (DCC) regions which follow the expansion of a high energy density region into the ``cold'' vacuum. The numerical study is based on the one-loop effective potential for the massive 2+1-dimensional Gross-Neveu model. We pay attention to the setting of the initial conditions and to determining which parameters are relevant for a strong amplification of the pion field. We find that the size of the ``hot'' source plays a significant role. For large enough source radii, we observe strong correlation phenomena, corresponding to the growth of large regions where the pion field oscillates along a given direction. We give our results in terms of the $θ$ angle which defines the DCC disorientation, of the other $O(4)$ angles distributions, of the local ratios $R_{a}=π_{a}^{2}/{\vecπ}^2$ $(a=1,2,3)$, and of the energies associated with the fields at representative times.

hep-ph

Thermodynamics of the Massive Gross-Neveu Model

We study the thermodynamics of massive Gross-Neveu models with explicitly broken discrete or continuous chiral symmetries for finite temperature and fermion densities. The large $N$ limit is discussed bearing attention to the no-go theorems for symmetry breaking in two dimensions which apply to the massless cases. The main purpose of the study is to serve as analytical orientation for the more complex problem of chiral transition in $4-$dimensional QCD with quarks. For any non-vanishing fermion mass we find, at finite densities, lines of first order phase transitions. For small mass values traces of would-be second order transitions and a tricritical point are recognizable. We study the thermodynamics of these models, and in the model with broken continuous chiral symmetry we examine the properties of the pion like state.

hep-th