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E. Megias

Publications and source records attributed to E. Megias.

At least 37 records · Page 2Linked to original sources
arXiv2014

Polyakov loop spectroscopy in the confined phase of gluodynamics and QCD

By using a simple relativistic model, we compute the glueball and gluelump spectra and relate these quantities, respectively, to the trace anomaly and Polyakov loop in the adjoint representation of gluodynamics. This spectroscopic description of thermodynamics is extended with the inclusion of quarks. The relation between the hadron resonance gas and the Polyakov loop in the fundamental and higher representations is addressed.

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arXiv2014

The Polyakov loop in various representations in the confined phase of QCD

We analyze the expectation value of the Polyakov loop in the fundamental and higher representations in the confined phase of QCD. We discuss a hadronic like representation, and find that the Polyakov loop corresponds to a partition function in the presence of a colored source, explaining its real and positive character. Saturating the sum rules to intermediate temperatures requires a large number of multipartonic excited states. By using constituent or bag models, we find detailed low temperature scaling rules which depart from the Casimir scaling and could be tested by lattice calculations.

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arXiv2013

Polyakov loop, Hadron Resonance Gas Model and Thermodynamics of QCD

We summarize recent results on the hadron resonance gas description of QCD. In particular, we apply this approach to describe the equation of state and the vacuum expectation value of the Polyakov loop in several representations. Ambiguities related to exactly which states should be included are discussed.

hep-ph↗
arXiv2013

Constituent Quarks and Gluons, Polyakov loop and the Hadron Resonance Gas Model

Based on first principle QCD arguments, it has been argued in arXiv:1204.2424[hep-ph] that the vacuum expectation value of the Polyakov loop can be represented in the hadron resonance gas model. We study this within the Polyakov-constituent quark model by implementing the quantum and local nature of the Polyakov loop hep-ph/0412308, hep-ph/0607338. The existence of exotic states in the spectrum is discussed.

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arXiv2013

Excited Hadrons, Heavy Quarks and QCD thermodynamics

We show how excited states in QCD can be profitably used to build up the Polyakov loop in the fundamental representation at temperatures below the hadron-quark-gluon crossover. The conditions under which a Hagedorn temperature for the Polyakov loop can be defined are analysed.

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arXiv2012

The hadron resonance gas model: thermodynamics of QCD and Polyakov loop

We study the hadron resonance gas model and describe the equation of state of QCD and the vacuum expectation value of the Polyakov loop in the confined phase, in terms of hadronic states with light quarks in the first case, and with exactly one heavy quark in the second case. Comparison with lattice simulations is made.

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arXiv2012

The Polyakov loop and the hadron resonance gas model

The Polyakov loop has been used repeatedly as an order parameter in the deconfinement phase transition in QCD. We argue that, in the confined phase, its expectation value can be represented in terms of hadronic states, similarly to the hadron resonance gas model for the pressure. Specifically, L(T) \approx 1/2\sum_αg_α\,e^(-Δ_α/T), where g_αare the degeneracies and Δ_αare the masses of hadrons with exactly one heavy quark (the mass of the heavy quark itself being subtracted). We show that this approximate sum rule gives a fair description of available lattice data with N_f=2+1 for temperatures in the range 150MeV<T<190MeV with conventional meson and baryon states from two different models. For temperatures below 150MeV different lattice results disagree. One set of data can be described if exotic hadrons are present in the QCD spectrum while other sets do not require such states.

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arXiv2011

Trouble Finding the Optimal AdS/QCD

In the bottom-up approach to AdS/QCD based on a five-dimensional gravity dilaton action the exponential of the dilaton field is usually identified as the strong or 't Hooft coupling. There is currently no model known which fits the measurements of the running coupling and lattice results for pressure at the same time. With a one parametric toy model we demonstrate the effect of fitting the pressure on the coupling and vice versa.

hep-th↗
arXiv2011

QCD-Thermodynamics using 5-dim Gravity

We calculate the critical temperature and free energy of the gluon plasma using the dilaton potential arXiv:0911.0627[hep-ph] in the gravity theory of AdS/QCD. The finite temperature observables are calculated in two ways: first, from the Page-Hawking computation of the free energy, and secondly using the Bekenstein-Hawking proportionality of the entropy with the area of the horizon. Renormalization is well defined, because the T=0 theory has asymptotic freedom. We further investigate the change of the critical temperature with the number of flavours induced by the change of the running coupling constant in the quenched theory. The finite temperature behaviour of the speed of sound, spatial string tension and vacuum expectation value of the Polyakov loop follow from the corresponding string theory in AdS_5.

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arXiv2010

Thermodynamics of 5D dilaton-gravity

We calculate the free energy, spatial string tension and Polyakov loop of the gluon plasma using the dilaton potential of Ref. arXiv:0911.0627[hep-ph] in the dilaton-gravity theory of AdS/QCD. The free energy is computed from the Black Hole solutions of the Einstein equations in two ways: first, from the Bekenstein-Hawking proportionality of the entropy with the area of the horizon, and secondly from the Page-Hawking computation of the free energy. The finite temperature behaviour of the spatial string tension and Polyakov loop follow from the corresponding string theory in AdS_5. Comparison with lattice data is made.

hep-th↗
arXiv2010

Thermodynamics of AdS/QCD within the 5D dilaton-gravity model

We calculate the pressure, entropy density, trace anomaly and speed of sound of the gluon plasma using the dilaton potential of Ref. arXiv:0911.0627[hep-ph] in the dilaton-gravity theory of AdS/QCD. The finite temperature observables are calculated from the Black Hole solutions of the Einstein equations, and using the Bekenstein-Hawking equality of the entropy with the area of the horizon. Renormalization is well defined, because the T=0 theory has asymptotic freedom. Comparison with lattice simulations is made.

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arXiv2010

Phenomenology of AdS/QCD and Its Gravity Dual

We construct the dilaton potential in the gravity dual theory of AdS/QCD for the warp factor of Refs.{1,2}. Using this AdS_5-metric with properties similar to QCD, we find that the gravity dual leads to a meaningful gauge coupling in the region between the charmonium and bottonium mass, but differs slightly from QCD in the extreme UV. When we fix the ultraviolet behavior in accord with the beta-function, we can obtain good agreement with the overall heavy quark-antiquark potential. Although the leading order proportional to -α^{4/3}/r differs from perturbative QCD, the full potential agrees quite well with the short distance QCD potential in NNLO.

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arXiv2009

Correlations between perturbation theory and power corrections in QCD at zero and finite temperature

The duality between QCD perturbative series and power corrections recently conjectured by Narison and Zakharov is analyzed. We propose to study correlations between both contributions as diagnostics tool. A very strong correlation between perturbative and non perturbative contributions is observed for several observables at zero and at finite temperature supporting the validity of the dual description.

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arXiv2009

The Heavy Quark Free-Energy at T<Tc in AdS/QCD

Starting with the modified AdS/QCD metric developed in Ref.[1] we use the Nambu-Goto action to obtain the free energy of a quark-antiquark pair at T<Tc, for which we show that the effective string tension goes to zero at Tc=154MeV.

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arXiv2009

Trace Anomaly, Thermal Power Corrections and Dimension Two condensates in the deconfined phase

The trace anomaly of gluodynamics on the lattice shows clear fingerprints of a dimension two condensate above the phase transition. The condensate manifests itself through even powers of the inverse temperature while the total perturbative contribution corresponds to a mild temperature dependence and turns out to be compatible with zero within errors. We try several resummation methods based on a renormalization group improvement. The trace anomaly data are analyzed and compared with other determinations of the dimension two condensate based on the Polyakov loop and the heavy qq free energy, yielding roughly similar numerical values. The role of glueballs near the transition is also discussed.

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arXiv2008

The Powers of Deconfinement

The trace anomaly of gluodynamics encodes the breakdown of classical scale invariance due to interactions around the deconfinement phase transition. While it is expected that at high temperatures perturbation theory becomes applicable we show that current lattice calculations are far from the perturbative regime and are dominated instead by inverse even power corrections in the temperature, while the total perturbative contribution is estimated to be extremely small and compatible with zero within error bars. We provide an interpretation in terms of dimension-two gluon condensate of the dimensionally reduced theory which value agrees with a similar analysis of power corrections from available lattice data for the renormalized Polyakov loop and the heavy quark-antiquark free energy in the deconfined phase of QCD.

hep-ph↗
arXiv2008

Trace Anomaly and dimension two gluon condensate above the phase transition

The dimension two gluon condensate has been used previously within a simple phenomenological model to describe power corrections from available lattice data for the renormalized Polyakov loop and the heavy quark-antiquark free energy in the deconfined phase of QCD (hep-ph/0505215,hep-ph/0702055). The QCD trace anomaly of gluodynamics also shows unequivocal inverse temperature power corrections which may be encoded as dimension two gluon condensate. We analyze lattice data of the trace anomaly and compare with other determinations of the condensate from previous references, yielding roughly similar numerical values.

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