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Joan Soto

Publications and source records attributed to Joan Soto.

At least 37 records · Page 2Linked to original sources
arXiv2016

Heavy Hybrids: decay to and mixing with Heavy Quarkonium

We report on a recent QCD based research on hybrid mesons containing $c\bar c$ or $b\bar b$ quarks. We present results for the spectrum, the decay widths to heavy quarkonium, and the role of mixing with the latter. We point out that mixing with heavy quarkonium provides a potentially large source of spin symmetry breaking. We identify candidates to hybrid mesons among the so called XYZ states in the charmonium and bottomonium spectrum.

hep-ph↗
arXiv2016

OSEFT or how to go beyond hard thermal loops

We show that effective field theory techniques can be applied in the high temperature $T$ regime of plasmas to improve the accuracy of the physics of the hard scales (or scales of order $T$), and as a by-product, also that of the soft scales (or scales of order $gT$). At leading order in the coupling constant the hard scales of the plasma can be viewed as on-shell classical particles. Based on this observation, and without any reference to the state of the system, we derive an effective field theory describing the quantum fluctuations around an on-shell fermion with energy $p$, described as a set of high dimension operators over the on-shell energy $p$. When applied to systems close to thermal equilibrium, where for most on-shell particles $p \sim T$, we show that the on-shell effective field theory (OSEFT) properly describes the HTL photon polarization tensor of QED, and its 1/T corrections. For the soft scales the first non-vanishing power correction turns out to be a perturbative correction to the HTL result.

hep-ph↗
arXiv2013

Heavy Quarkonium moving in a Quark-Gluon Plasma

By means of effective field theory techniques, we study the modifications of some properties of weakly coupled heavy quarkonium states propagating through a quark-gluon plasma at temperatures much smaller than the heavy quark mass, m_Q. Two different cases are considered, corresponding to two different hierarchies between the typical size of the bound state, r, the binding energy, E, the temperature, T, and the screening mass, m_D. The first case corresponds to the hierarchy m_Q >> 1/r >> T >> E >> m_D, relevant for moderate temperatures, and the second one to the hierarchy m_Q >> T >> 1/r, m_D >> E, relevant for studying the dissociation mechanism. In the first case we determine the perturbative correction to the binding energy and to the decay width of states with arbitrary angular momentum, finding that the width is a decreasing function of the velocity. A different behavior characterizes the second kinematical case, being the width of s-wave states a non-monotonic function of the velocity, increasing at moderate velocities and decreasing in the ultra-relativistic limit. We obtain a simple analytical expression of the decay width for T >> 1/r >> m_D >> E at moderate velocities, and we derive the s-wave spectral function for the more general case T >> 1/r, m_D >> E. A brief discussion of the possible experimental signatures as well as a comparison with the relevant lattice data are also presented.

hep-ph↗
arXiv2012

Determination of alpha_s from the QCD static energy

We compare lattice data for the short-distance part of the static energy in 2+1 flavor quantum chromodynamics (QCD) with perturbative calculations, up to next-to-next-to-next-to leading-logarithmic accuracy. We show that perturbation theory describes very well the lattice data at short distances, and exploit this fact to obtain a determination of the product of the lattice scale r_0 with the QCD scale Lambda_{MS}. With the input of the value of r_0, this provides a determination of the strong coupling alpha_s at the typical distance scale of the lattice data. We obtain alpha_s(1.5 GeV)=0.326\pm0.019, which provides a novel determination of alpha_s at low energy and with three-loop accuracy (including resummation of the leading ultrasoft logarithms). When this value is evolved to the Z-mass scale M_Z, it corresponds to alpha_s(M_Z)=0.1156^{+0.0021}_{-0.0022}.

hep-ph↗
arXiv2012

Precision determination of r_0Lambda_MS from the QCD static energy

We use the recently obtained theoretical expression for the complete QCD static energy at next-to-next-to-next-to leading-logarithmic accuracy to determine r_0Lambda_MS by comparison with available lattice data, where r_0 is the lattice scale and Lambda_MS is the QCD scale. We obtain r_0Lambda_MS=0.637^{+0.032}_{-0.030} for the zero-flavor case. The procedure we describe can be directly used to obtain r_0Lambda_MS in the unquenched case, when unquenched lattice data for the static energy at short distances becomes available. Using the value of the strong coupling alpha_s as an input, the unquenched result would provide a determination of the lattice scale r_0.

hep-ph↗
arXiv2012

On the quark mass dependence of nucleon-nucleon S-wave scattering lengths

In the framework of a Chiral effective theory with dibaryon fields, we calculate the pion mass dependence of the inverse scattering length of the nucleon-nucleon system in the $^3S_1$ channel at order ${(m_π^3 / Λ_χ^2)}\times (m_π^{1/2}m_N^{3/2}/8πf_π^2)^n$ for all $n\ge 0$. We show that certain sets of potentially large higher order contributions vanish. We discuss the difficulties of extending the proof to the $^1S_0$ channel. We apply our results to chiral extrapolations of current lattice data.

nucl-th↗
arXiv2011

Non-relativistic bound states in a moving thermal bath

We study the propagation of non-relativistic bound states moving at constant velocity across a homogeneous thermal bath and we develop the effective field theory which is relevant in various dynamical regimes. We consider values of the velocity of the bound state ranging from moderate to highly relativistic and temperatures at all relevant scales smaller than the mass of the particles that form the bound state. In particular, we consider two distinct temperature regimes, corresponding to temperatures smaller or higher than the typical momentum transfer in the bound state. For temperatures smaller or of the order of the typical momentum transfer, we restrict our analysis to the simplest system, a hydrogen-like atom. We build the effective theory for this system first considering moderate values of the velocity and then the relativistic case. For large values of the velocity of the bound state, the separation of scales is such that the corresponding effective theory resembles the soft collinear effective theory (SCET). For temperatures larger than the typical momentum transfer we also consider muonic hydrogen propagating in a plasma which contains photons and massless electrons and positrons, so that the system resembles very much heavy quarkonium in a thermal medium of deconfined quarks and gluons. We study the behavior of the real and imaginary part of the static two-body potential, for various velocities of the bound state, in the hard thermal loop approximation. We find that Landau damping ceases to be the relevant mechanism for dissociation from a certain "critical" velocity on in favor of screening. Our results are relevant for understanding how the properties of heavy quarkonia states produced in the initial fusion of partons in the relativistic collision of heavy ions are affected by the presence of an equilibrated quark-gluon plasma.

hep-ph↗
arXiv2011

The discrete contribution to $ψ^{\prime}\to J/ψ+γγ$

The decay mode $ψ(2S)\to J/ψ+γγ$ is proposed in order to experimentally identify the effects of the coupling of charmonium states to the continuum $D\bar D$ states. To have a better understanding of such a two-photon decay process, in this work we restrict ourselves to investigate the contribution of the discrete part, in which the photons are mainly produced via the intermediate states $χ_{cJ}(nP)$. Besides calculating the resonance contributions of $χ_{cJ}(1P)\; (J=0,1,2)$, we also take into account the contributions of the higher excited states $χ_{cJ}(2P)$ and the interference effect among the 1P and 2P states. We find that the contribution of the 2P states and the interference terms to the total decay width is very tiny. However, for specific regions of the Dalitz plot, off the resonance peaks, we find that these contributions are sizable and should also be accounted for. We also provide the photon spectrum and study the polarization of $J/ψ$.

hep-ph↗
arXiv2010

Non-relativistic bound states at finite temperature (II): the muonic hydrogen

We illustrate how to apply modern effective field theory techniques and dimensional regularization to factorise the various scales which appear in QED bound states at finite temperature. We focus here on the muonic hydrogen atom. Vacuum polarization effects make the physics of this atom at finite temperature very close to that of heavy quarkonium states. We comment on the implications of our results for these states in the quark gluon plasma. In particular, we estimate the effects of a finite charm quark mass in the dissociation temperature of bottomonium.

hep-ph↗
arXiv2010

Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature

We calculate the heavy quarkonium energy levels and decay widths in a quark-gluon plasma, whose temperature T and screening mass m_D satisfy the hierarchy m alpha_s >> T >> m alpha_s^2 >> m_D (m being the heavy-quark mass), at order m alpha_s^5. We first sequentially integrate out the scales m, m alpha_s and T, and, next, we carry out the calculations in the resulting effective theory using techniques of integration by regions. A collinear region is identified, which contributes at this order. We also discuss the implications of our results concerning heavy quarkonium suppression in heavy ion collisions.

hep-ph↗
arXiv2010

Effective Field Theory with Dibaryon Fields: Nucleon-Nucleon amplitudes at NNLO

We calculate the nucleon-nucleon scattering amplitudes in the 1S0 and 3S1-3D1 channels at next-to-next to leading order starting from a recently proposed non-relativistic chiral effective theory, which includes dibaryon fields as fundamental degrees of freedom. We restrict ourselves to center of mass energies (E) smaller than the pion mass (m_pi), and further divide the calculation into two relative momentum (p) regions, a high energy one p ~ m_pi >> delta m_i, δm_i being the dibaryon residual masses, and low energy one p ~ delta m_i. We first match to a lower energy effective theory in which we calculate the amplitudes in the high energy region. We further match this effective theory to the so called pionless effective theory in the low energy region, and carry out the calculations in the latter. Dimensional regularization and minimal subtraction scheme are used throughout. For 1S0 channel a good description of the phase shift data is obtained for E < 50 MeV. For the 3S1-3D1 channel, the 3S1 phase shift data is only well described up to E < 20 MeV.

nucl-th↗
arXiv2009

The QCD static energy at NNNLL

We compute the static energy of QCD at short distances at next-to-next-to-next-to leading-logarithmic accuracy in terms of the three-loop singlet potential. By comparing our results with lattice data we extract the value of the unknown piece of the three-loop singlet potential.

hep-ph↗
arXiv2009

Effective string theory constraints on the long distance behavior of the subleading potentials

The dynamics of heavy quarkonium systems in the strong coupling regime reduces to a quantum mechanical problem with a number of potentials which may be organized in powers of 1/m, m being the heavy quark mass. The potentials must be calculated non-perturbatively, for instance in lattice QCD. It is well known that the long distance behavior of the static (1/m^0) potential is well reproduced by an effective string theory. We show that this effective string theory, if correct, should also reproduce the long distance behavior of all 1/m suppressed potentials. We demonstrate the practical usefulness of this result by finding a suitable parameterization of the recently calculated 1/m potential. We also calculate the 1/m^2 velocity dependent and spin dependent potentials. Once Poincaré invariance is implemented, the shapes of most of the spin independent potentials are fully predicted in terms of the string tension, and the shapes of the spin dependent ones in terms of a single parameter.

hep-ph↗
arXiv2008

Non-relativistic bound states at finite temperature (I): the hydrogen atom

We illustrate how to apply modern effective field theory techniques and dimensional regularization to factorize the various scales which appear in non-relativistic bound states at finite temperature. We focus here on the simplest case: the hydrogen atom. We discuss in detail the interplay of the hard, soft and ultrasoft scales of the non-relativistic system at zero temperature with the additional scales induced at finite temperature. We also comment on the implications of our results for heavy quarkonium bound states in the quark gluon plasma.

hep-ph↗
arXiv2008

Taking dibaryon fields seriously

We propose a low energy effective field theory of QCD at the scale of pion mass for the $N_B=2$ sector, $N_B$ being the baryon number, which contains two dibaryon fields in addition to the nucleons and pions. It has a well defined counting, is renormalizable and the nucleon-nucleon scattering amplitudes are manifestly unitary at leading order. We work out a lower energy effective theory for nucleons with energy much lower than the pion mass and three momentum comparable to it, which also has a well defined counting and is renormalizable. The dibaryon fields must also be kept as explicit degrees of freedom in this theory. We calculate the scattering amplitudes at next-to-leading order for the $^1S_0$ and $^3S_1$ channels in this framework and obtain an excellent description of the phase shifts for center of mass energies in the $0-50 MeV$ range.

nucl-th↗
arXiv2007

The nucleon-nucleon potential beyond the static approximation

We point out that, due to the use of static nucleon propagators in Heavy Baryon Chiral Perturbation Theory, the current calculations of the nucleon-nucleon potential miss certain contributions starting at two loops. These contributions give rise to contact interactions, which are both parametrically and numerically more important than the so called NNLO potentials. They show a peculiar dependence on the light quark masses, which should be taken into account when performing chiral extrapolations of lattice data. However, they do not appear to have an impact on phenomenology since they can be absorbed into redefinitions of unknown parameters which are usually fitted to data.

nucl-th↗