Search

Hot axions, thermally produced in the Early Universe, would contribute to dark radiation and are thus subject to present and future constraints from $N_{\rm eff}$. In this paper we quantify the contribution to $N_{\rm eff}$ and its uncertainty in models with axion-gluon couplings from thermal dynamics above the QCD transition. In more detail, we determine the leading-order thermal axion production rate for axion momenta of the order of the temperature adopting three different schemes for the incorporation of the collective dynamics of soft gluons. We show how these three schemes extrapolate differently into the regime of softer axion production, thus giving us a quantitative handle on the theory uncertainty of the rate. Upon solving the Boltzmann equation, we find that this theory uncertainty translates to an uncertainty of at most 0.002 for $N_{\rm eff}$. The uncertainty from common momentum-averaged approximations to the Boltzmann equation is smaller. We also comment on existing rate determinations in the literature and discuss how QCD transition dynamics would need to be integrated into our results., Comment: 23 pages + appendices, 9 figures

High-energy particles traversing the Quark-Gluon plasma experience modified (massive) dispersion, although their vacuum mass is negligible compared to the kinetic energy. Due to poor convergence of the perturbative series in the regime of soft loop momenta, a more precise determination of this effective mass is needed. This paper continues our investigation on the factorisation between strongly-coupled infrared classical and perturbative ultraviolet behavior. The former has been studied non-perturbatively within EQCD by determining a non-local operator on the lattice. By computing the temperature-scale contribution to the same operator in 4D QCD at next-to-leading order (NLO), we remove the ultraviolet divergence of the EQCD calculation with an opposite infrared divergence from the hard thermal scale. The result is a consistent, regulator-independent determination of the classical contribution where the emergence of new divergences signals sensitivities to new regions of phase space. We address the numerical impact of the classical and NLO thermal corrections on the convergence of the factorised approach and on the partial applicability of our results to calculations of transport coefficients., Comment: 42 pages, 2 figures, 2 tables. v2: clarifications added, minor typographical fixes, matches JHEP version

The in-medium dispersion of hard partons, encoded in their so-called asymptotic mass, receives large non-perturbative contributions from classical gluons, i.e. soft gluons with large occupation numbers. Here, we discuss how the analytical properties of thermal amplitudes allow for a non-perturbative determination of the infrared classical contribution through lattice determinations in the dimensionally-reduced effective theory of hot QCD, EQCD. We show how these lattice determinations need to be complemented by perturbative two-loop matching calculations between EQCD and QCD, so that the unphysical (classical) ultraviolet behavior of EQCD is replaced by its proper quantum QCD counterpart. We show how lattice and perturbative EQCD are in good agreement in the UV and present an outlook on the two-loop quantum QCD contribution., Comment: 6 pages, to appear in the proceedings of Hard Probes 2023

The climate crisis and the degradation of the world's ecosystems require humanity to take immediate action. The international scientific community has a responsibility to limit the negative environmental impacts of basic research. The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics, and Hadron and Nuclear Physics) make use of common and similar experimental infrastructure, such as accelerators and observatories, and rely similarly on the processing of big data. Our communities therefore face similar challenges to improving the sustainability of our research. This document aims to reflect on the environmental impacts of our work practices and research infrastructure, to highlight best practice, to make recommendations for positive changes, and to identify the opportunities and challenges that such changes present for wider aspects of social responsibility., Comment: 158 pages, 21 figures; comments welcome. Revisions included in Version 2.0 are detailed on page 3 of the pdf. If you would like to endorse this document please visit: https://sustainable-hecap-plus.github.io/. An HTML version of this document is available at: https://sustainable-hecap-plus.github.io/

The thermal plasma in the early universe produced a stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). In previous works only single graviton production processes that contribute to the CGMB have been considered. Here we also investigate graviton pair production processes and show that these can lead to a significant contribution if the ratio between the maximum temperature and the Planck mass, $T_{\rm max}/m_{\rm p}$, divided by the internal coupling in the heat bath is large enough. As the dark matter freeze-in production mechanism is conceptually very similar to the GW production mechanism from the primordial thermal plasma, we refer to the latter as ``GW freeze-in production''. We show that quantum gravity effects appear in single graviton production and are smaller by a factor $(T_{\rm max}/m_{\rm p})^2$ than the leading order contribution. In our work we explicitly compute the CGMB spectrum within a scalar model with quartic interaction., Comment: 18 pages, 6 figures (matches version published in Phys. Rev. D)

We employ the QCD kinetic theory, including next-to-leading(NLO) order corrections in coupling constant, to study the evolution of weakly coupled non-Abelian plasmas towards thermal equilibrium. For two characteristic far-from-equilibrium systems with either under- or over-occupied initial conditions, the NLO corrections remain well under control for a wide range of couplings, and the overall effect of NLO corrections is a reduction in the time required for thermalization.

I present an overview of recent developments in the microscopic description of the quark-gluon plasma. I will concentrate on medium-induced emission and transverse momentum broadening. These are two key ingredients of the theory of jet modifications in the QCD medium and of the kinetic theory used for transport and thermalisation. The main focus is on progress towards a better understanding of theory and of its uncertainties., Comment: Presented at Quark Matter 2022, to appear in the proceedings. 8 pages, 3 figures

The transverse momentum broadening coefficient $\hat{q}$ receives both soft, classical and radiative, quantum corrections. The former are responsible for a large O(g) correction, whereas the latter enter at relative order $\alpha_s$, but are enhanced by a double logarithm of the length of the medium over the thermal wavelength. We analyze radiative corrections for a weakly-coupled quark-gluon plasma. We find that a thermal population of dynamical gluons changes the boundaries and reduces the size of the double-logarithmic phase space. It also provides new subdominant logarithmic corrections. We also show how the quantum, double-logarithmic and classical, soft phase spaces are smoothly connected once the radiated gluon becomes soft enough. Finally, we discuss a pathway to a determination of radiative corrections beyond the harmonic-oscillator approximation., Comment: 26 pages plus appendices, 9 figures. v2: minor typographical fixes, matches JHEP version

The baryon asymmetry of the Universe is one of the central motivations to expect physics beyond the Standard Model. In this Snowmass white paper, we review the challenges and opportunities in testing some of the central paradigms that predict physics at scales low enough to expect new experimental data in the next decade. Focusing on theoretical ideas and some of their experimental implications, in particular, we discuss neutron-antineutron transformations, flavor observables, next generation colliders, future neutron facilities, gravitational waves, searches for permanent electric dipole moments, $0\nu \beta \beta $ decay and some future large underground experiments as methods to test post-sphaleron baryogenesis, electroweak baryogenesis, mesogenesis and low scale leptogenesis. Finally, we comment on the cases where high scale physics can be probed through some of these same mechanisms., Comment: White paper to be submitted to the Snowmass Process' Rare Processes and Precision Measurements Frontier, Baryon and Lepton Number Violation Topical Group (This v2 version corrects a missing author and an author's name which was misspelled. Apologies to these authors for this oversight on the part of the submitter!)

High-energy particles traversing a medium experience modified dispersion. In the Quark-Gluon Plasma, such dispersion affects jet propagation and transport properties and should be determined better. Above $\sim 2T_c$ we expect strongly coupled infrared behavior and perturbative ultraviolet behavior, allowing a perturbative matching to an effective theory called EQCD, which can be studied non-perturbatively. We study the relevant non-local operator in EQCD at next-to-leading order which allows for a complete EQCD-to-lattice match and prepares the groundwork for a matching between EQCD and full QCD. Our results in EQCD show remarkable agreement between perturbation theory and the lattice in the expected regime., Comment: 34 pages, 3 figures, 4 tables. Updates of (i) the NLO perturbative result in eq. (4.12), (ii) the numerical integration in eq. (5.2), (iii) numerical values in tabs. 1 and 3, and (iv) figures. Conclusions unchanged

We provide the first next-to-leading-order (NLO) weak-coupling description of the thermalization process of far-from-equilibrium systems in non-abelian gauge theory. We study isotropic systems starting from either over- or under-occupied initial conditions and follow their time evolution towards thermal equilibrium by numerically solving the QCD effective kinetic theory at NLO accuracy. We find that the NLO corrections remain well under control for a wide range of couplings and that the overall effect of NLO corrections is to reduce the time needed to reach thermal equilibrium in the systems considered., Comment: 9 Pages and two figures

When dark matter particles only feebly interact with plasma constituents in the early universe, they never reach thermal equilibrium. As opposed to the freeze-out mechanism, where the dark matter abundance is determined at $T \ll M$, the energy density of a feebly interacting state builds up and increases over $T \gtrsim M$. In this work, we address the impact of the high-temperature regime on the dark matter production rate, where the dark and Standard Model particles are ultra-relativistic and nearly light-like. In this setting, multiple soft scatterings, as well as $2 \to 2$ processes, are found to give a large contribution to the production rate. Within the model we consider in this work, namely a Majorana fermion dark matter of mass $M$ accompanied by a heavier scalar $-$ with mass splitting $\Delta M$ $-$ which shares interactions with the visible sector, the energy density can be dramatically underestimated when neglecting the high-temperature dynamics. We find that the overall effective $1 \leftrightarrow 2$ and $2 \to2$ high-temperature contributions to dark-matter production give $\mathcal{O}(10)$ (20\%) corrections for $\Delta M /M =0.1$ ($\Delta M /M =10$) to the Born production rate with in-vacuum masses and matrix elements. We also assess the impact of bound-state effects on the late-time annihilations of the heavier scalar, in the context of the super-WIMP mechanism., Comment: 43 pages, 14 figures, journal version

In this review article, we discuss the current status and future prospects of perturbation theory as a means of studying the equilibrium thermodynamic and near-equilibrium transport properties of deconfined QCD matter. We begin with a brief introduction to the general topic, after which we review in some detail the foundations and modern techniques of the real- and imaginary-time formalisms of thermal field theory, covering e.g. the different bases used in the real-time formalism and the resummations required to deal with soft and collinear contributions. After this, we discuss the current status of applications of these techniques, including topics such as electromagnetic rates, transport coefficients, jet quenching, heavy quarks and quarkonia, and the Equations of State of hot quark-gluon plasma as well as cold and dense quark matter. Finally, we conclude with our view of the future directions of the field, i.e. how we anticipate perturbative calculations to contribute to our collective understanding of strongly interacting matter in the coming years., Comment: 137 pages, 44 figures. v4: Version published in Physics Reports; two typographical errors corrected from v3

Brambilla, Escobedo, Soto, and Vairo have derived an effective description of quarkonium with two parameters; a momentum diffusion term and a real self-energy term. We point out that there is a similar real self-energy term for a single open heavy flavor and that it can be expressed directly in terms of Euclidean electric field correlators along a Polyakov line. This quantity can be directly studied on the lattice without the need for analytical continuation. We show that Minkowski-space calculations of this correlator correspond with the known NLO Euclidean value of the relevant electric field two-point function and that it differs from the real self-energy term for quarkonium., Comment: 5 pages, 1 figure. v2: very minor edits, matches journal version. v3: Eqs. (11) and (17) of v2 fixed, title and abstract modified, conclusions changed

Following Caron-Huot and combining results for the thermal dependence of spectral functions at large time-like momenta, we write an explicit expression for the thermal width of the Higgs boson to $\mathcal{O}(\alpha_\mathrm{s})$ for $T \ll M_H$. It is an $\mathcal{O}( \alpha_\mathrm{s} (T/M_H)^4 )$ correction for $H\to gg$ and $H\to q\bar{q}$. We also compile corresponding results for the thermal width of the $Z$-boson, and we recall which generic structures of the field theory, accessible via the operator product expansion, fix the $T/M$-dependence of the decay of heavy particles., Comment: 5 pages plus appendices. v2: minor modifications, version accepted for publication in PRD

We compute O(g) NLO corrections to the transverse scattering kernel and transverse momentum broadening coefficient $\hat{q}$ of weakly-coupled $\mathcal{N}=4$ SYM. Based on this, we also compute NLO correction to the collinear splitting rates. For $\hat{q}$ we find that the NLO/LO ratio is similar to the QCD one, with large NLO corrections. This is contrasted by our findings for the collinear splitting rate, which show a much better convergence in SYM than in QCD, providing further support to earlier expectations that NLO corrections have signs and relative magnitudes controlled by the specifics of the theory. We also compare the ratio of $\hat{q}$ in QCD and in $\mathcal{N}=4$ theory to strong coupling expectations., Comment: 22 pages plus appendices, 12 figures. v2: minor changes, version accepted for publication on JHEP

We compute the hydrodynamic relaxation times $\tau_\pi$ and $\tau_j$ for hot QCD at next-to-leading order in the coupling with kinetic theory. We show that certain dimensionless ratios of second-order to first-order transport coefficients obey bounds which apply whenever a kinetic theory description is possible; the computed values lie somewhat above these bounds. Strongly coupled theories with holographic duals strongly violate these bounds, highlighting their distance from a quasiparticle description., Comment: 5 pages, 3 figures. v2: note and reference added, version accepted for publication on Phys. Rev. Lett

We compute the shear viscosity of QCD with matter, including almost all next-to-leading order corrections -- that is, corrections suppressed by one power of $g$ relative to leading order. We argue that the still missing terms are small. The next-to-leading order corrections are large and bring $\eta/s$ down by more than a factor of 3 at physically relevant couplings. The perturbative expansion is problematic even at $T \simeq 100$ GeV. The largest next-to-leading order correction to $\eta/s$ arises from modifications to the qhat parameter, which determines the rate of transverse momentum diffusion. We also explore quark number diffusion, and shear viscosity in pure-glue QCD and in QED., Comment: 36 pages plus appendices, 11 figures. The main results are summarized in the introduction (Fig. 1)

In many realizations of leptogenesis, heavy right-handed neutrinos play the main role in the generation of an imbalance between matter and antimatter in the early Universe. Hence, it is relevant to address quantitatively their dynamics in a hot and dense environment by taking into account the various thermal aspects of the problem at hand. The strong washout regime offers an interesting framework to carry out calculations systematically and reduce theoretical uncertainties. Indeed, any matter-antimatter asymmetry generated when the temperature of the hot plasma $T$ exceeds the right-handed neutrino mass scale $M$ is efficiently erased, and one can focus on the temperature window $T \ll M$. We review recent progresses in the thermal field theoretic derivation of the key ingredients for the leptogenesis mechanism: the right-handed neutrino production rate, the CP asymmetry in the heavy-neutrino decays and the washout rates. The derivation of evolution equations for the heavy-neutrino and lepton-asymmetry number densities, their rigorous formulation and applicability are also discussed., Comment: 31 pages, 6 figures. Chapter 4 of the review volume "Leptogenesis: Current Challenges for Model Building, Phenomenology and Non-Equilibrium Field Theory"

We present an extension of the Arnold-Moore-Yaffe kinetic equations for jet energy loss to NLO in the strong coupling constant. A novel aspect of the NLO analysis is a consistent description of wider-angle bremsstrahlung (semi-collinear emissions), which smoothly interpolates between 2<->2 scattering and collinear bremsstrahlung. We describe how many of the ingredients of the NLO transport equations (such as the drag coefficient) can be expressed in terms of Wilson line operators and can be computed using a Euclidean formalism or sum rules, both motivated by the analytic properties of amplitudes at light-like separations. We conclude with an outlook on the computation of the shear viscosity at NLO., Comment: 4 pages, 4 figures. To appear in the proceedings of Quark Matter 2015 (Kobe, Japan)

We report on a recent next-to-leading order perturbative determination of the dilepton rate from a hot QCD plasma for frequency and momentum of the order of the temperature and for much smaller invariant mass $M\sim gT$. We briefly review the calculation, which generalizes the previous one for the photon case ($M=0$). We then analyze the consequences of the new calculation for the extraction of the photon rate from the small mass dilepton measurements. We then review a recent NLO determination at large $M$ and we show how to match and merge its results with the low-mass ones, resulting in a single rate which is NLO-accurate over the phenomenologically relevant region., Comment: 4 pages, 6 figures. To appear in the Hard Probes 2015 proceedings

We present an extension to next-to-leading order in the strong coupling constant $g$ of the AMY effective kinetic approach to the energy loss of high momentum particles in the quark-gluon plasma. At leading order, the transport of jet-like particles is determined by elastic scattering with the thermal constituents, and by inelastic collinear splittings induced by the medium. We reorganize this description into collinear splittings, high-momentum-transfer scatterings, drag and diffusion, and particle conversions (momentum-preserving identity-changing processes). We show that this reorganized description remains valid to NLO in $g$, and compute the appropriate modifications of the drag, diffusion, particle conversion, and inelastic splitting coefficients. In addition, a new kinematic regime opens at NLO for wider-angle collinear bremsstrahlung. These semi-collinear emissions smoothly interpolate between the leading order high-momentum-transfer scatterings and collinear splittings. To organize the calculation, we introduce a set of Wilson line operators on the light-cone which determine the diffusion and identity changing coefficients, and we show how to evaluate these operators at NLO., Comment: 37 pages plus appendices, 15 figures. A pedagogical review has been presented in arXiv:1502.03730. v2: minor changes, matches journal version

We present an overview of a perturbative-kinetic approach to jet propagation, energy loss, and momentum broadening in a high temperature quark-gluon plasma. The leading-order kinetic equations describe the interactions between energetic jet-particles and a non-abelian plasma, consisting of on-shell thermal excitations and soft gluonic fields. These interactions include 2<->2 scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show how the contribution from the soft gluonic fields can be factorized into a set of Wilson line correlators on the light cone. We review recent field-theoretical developments, rooted in the causal properties of these correlators, which simplify the calculation of the appropriate Wilson lines in thermal field theory. With these simplifications lattice measurements of transverse momentum broadening have become possible, and the kinetic equations describing parton transport have been extended to next-to-leading order in the coupling g., Comment: Review to appear in QGP5, 40 pages, 12 figures

We present a computation, within weakly-coupled thermal QCD, of the production rate of low invariant mass ($M^2 \sim g^2 T^2$) dileptons, at next-to-leading order (NLO) in the coupling (which is $O(g^3 e^2 T^2)$). This involves extending the NLO calculation of the photon rate which we recently presented to the case of small nonzero photon invariant mass. Numerical results are discussed and tabulated forms and code are provided for inclusion in hydrodynamical models. We find that NLO corrections can increase the dilepton rate by up to 30-40% relative to leading order. We find that the electromagnetic response of the plasma for real photons and for small invariant mass but high energy dilepton pairs (e.g., $M^2 < (300\:\mathrm{MeV})^2$ but $p_T > 1 \: \mathrm{GeV}$) are close enough that dilepton pair measurements really can serve as Ersatz photon measurements. We also present a matching a la Ghisoiu and Laine between our results and results at larger invariant masses., Comment: 24 pages plus appendices, 17 figures. v2: fixed a caption, removed unneeded .pdf files. v3: minor clarifications, matches journal version

A brief overview of the calculation of photon and dilepton production rates in a deconfined quark-gluon plasma is presented. We review leading order rates as well as recent NLO determinations and non-equilibrium corrections. Furthermore, the difficulties in a non-perturbative lattice determination are summarized., Comment: 8 pages, to appear in the proceedings of Quark Matter 2014

We summarize the recent determination to next-to-leading order of the thermal photon rate at weak coupling. We emphasize how it can be expressed in terms of gauge-invariant condensates on the light cone, which are amenable to novel sum rules and Euclidean techniques. For the phenomenologically interesting value of alpha_s=0.3, the NLO correction represents a 20% increase and has a functional form similar to the LO result., Comment: 6 pages, 7 figures. Invited plenary talk at Hard Probes 2013, Stellenbosch, South Africa, Nov. 4-8, 2013. To appear in the conference proceedings by Nuclear Physics A

A brief overview of the theory of charmonium suppression in heavy ion collisions is presented. In particular I will concentrate on the effects caused by the hot, deconfined medium and on the effort to treat them using field-theoretical, QCD-based techniques, such as lattice QCD and Effective Field Theories., Comment: 10 pages, 4 figures, to appear in the proceedings of The 6th International Workshop on Charm Physics (CHARM 2013)

Heavy quarkonium is one of the most investigated probes of the medium produced in heavy-ion collisions. In the past few years progress has been made in the description of its in-medium dynamics from QCD. Non-relativistic EFTs in particular allow one to define and compute rigorously the potential governing the real-time evolution of the bound state from QCD, showing that it is composed of a real and an imaginary part. The latter encodes the effect of scattering with the light constituents of the plasma and is oftentimes responsible for the dissociation of the bound state. The EFT approach and its main results, as well as comparisons with recent lattice data and phenomenological applications, are briefly reviewed here., Comment: 14 pages, 4 figures. Invited talk at the Xth Quark Confinement and the Hadron Spectrum, October 8-12, 2012, Munich, Germany. v2: minor rewordings and terminology changes

In a weak-coupling effective field theory framework we study quarkonium dissociation induced by inelastic scattering with partons in the medium. This is the dominant dissociation process for temperatures such that the Debye mass is larger than the binding energy. We evaluate the dissociation cross section and the corresponding thermal decay width. At leading order we derive a convolution formula relating the two, which is consistent with the optical theorem and QCD at finite temperature. Bound state effects are systematically included. They add contributions to the cross section and width that are beyond a quasi-free approximation, whose validity is critically reviewed. For temperatures such that the Debye mass is smaller than the binding energy, the dominant dissociation mechanism is gluo-dissociation consisting in quarkonium dissociation induced by the absorbtion of a gluon from the medium. We calculate the gluo-dissociation cross section and width at next-to-leading-order accuracy., Comment: 33 pages. 11 figures

We compute the next-to-leading order O(g) correction to the thermal photon production rate in a QCD plasma. The NLO contributions can be expressed in terms of gauge invariant condensates on the light cone, which are amenable to novel sum rules and Euclidean techniques. We expect these technologies to be generalizable to other NLO calculations. For the phenomenologically interesting value of alpha_s=0.3, the NLO correction represents a 20% increase and has a functional form similar to the LO result., Comment: 41 pages plus appendices, 23 figures

In finite-temperature field theory, the cyclic Wilson loop is defined as a rectangular Wilson loop spanning the whole compactified time direction. In a generic non-abelian gauge theory, we calculate the perturbative expansion of the cyclic Wilson loop up to order g^4. At this order and after charge renormalization, the cyclic Wilson loop is known to be ultraviolet divergent. We show that the divergence is not associated with cusps in the contour but is instead due to the contour intersecting itself because of the periodic boundary conditions. One consequence of this is that the cyclic Wilson loop mixes under renormalization with the correlator of two Polyakov loops. The resulting renormalization equation is tested up to order g^6 and used to resum the leading logarithms associated with the intersection divergence. Implications for lattice studies of this operator, which may be relevant for the phenomenology of quarkonium at finite temperature, are discussed., Comment: 30 pages, 21 figures. Reference and note added, journal version

Quarkonium suppression is one of the most investigated probes of the medium produced in heavy-ion collisions. In this thesis we extend the well-established and successful zero temperature framework of Non-Relativistic (NR) Effective Field Theories (EFTs) (NRQCD, pNRQCD) for the study of heavy quarkonia (production, spectroscopy, decays, ...) to finite temperatures. This is achieved by integrating out in sequence the scales that characterize a NR bound state and those that are typical of a thermal medium, in the possible hierarchies that are relevant for quarkonia in the quark-gluon plasma. Within this framework we show how the potential that governs the evolution of the quark-antiquark pair is derived from QCD in a modern and rigorous way, thereby bridging the gap between phenomenological potential models and QCD. We show how the EFTs can be systematically improved and how effects that cannot be encoded in a potential arise naturally in the EFT, giving rise to new mechanisms of dissociation. We use this EFT framework to compute the spectrum and width of quarkonia in a particular setting that is relevant for the phenomenology of the ground states of bottomonium at the LHC. We also analyze within this framework the correlator of Polyakov loops, which is related to the thermodynamical free energy of heavy quark-antiquark pairs in the medium. As such, lattice computations thereof were frequently used as input for potential models. With our approach we are able to clarify the relation between these free energies and the real-time potential describing the dynamics of quarkonia, finding that the two are different not only in the important imaginary parts, that the former completely lack, but also in the real parts., Comment: PhD thesis, Technical University of Munich. 230 pages

The thermal width of heavy-quarkonium bound states in a quark-gluon plasma has been recently derived in an effective field theory approach. Two phenomena contribute to the width: the Landau damping phenomenon and the break-up of a colour-singlet bound state into a colour-octet heavy quark-antiquark pair by absorption of a thermal gluon. In the paper, we investigate the relation between the singlet-to-octet thermal break-up and the so-called gluo-dissociation, a mechanism for quarkonium dissociation widely used in phenomenological approaches. The gluo-dissociation thermal width is obtained by convoluting the gluon thermal distribution with the cross section of a gluon and a 1S quarkonium state to a colour octet quark-antiquark state in vacuum, a cross section that at leading order, but neglecting colour-octet effects, was computed long ago by Bhanot and Peskin. We will, first, show that the effective field theory framework provides a natural derivation of the gluo-dissociation factorization formula at leading order, which is, indeed, the singlet-to-octet thermal break-up expression. Second, the singlet-to-octet thermal break-up expression will allow us to improve the Bhanot--Peskin cross section by including the contribution of the octet potential, which amounts to include final-state interactions between the heavy quark and antiquark. Finally, we will quantify the effects due to final-state interactions on the gluo-dissociation cross section and on the quarkonium thermal width., Comment: 17 pages, 6 figures

We report a recent calculation of the heavy quarkonium energy levels and decay widths in a quark- gluon plasma whose temperature is much smaller than the inverse radius of the bound state, based on a Non-Relativistic Effective Field theory framework for heavy quarkonium at finite temperature. Relevance for the phenomenology of the Y(1S) in heavy ion collisions is also discussed., Comment: 5 pages, 1 figure, references added. Proceedings of the XIV International Conference on Hadron Spectroscopy (Hadron2011), 13-17 June 2011, Munich, Germany

Heavy quarkonium at finite temperature has been the subject of intense theoretical studies, for it provides a potentially clean probe of the quark-gluon plasma. Recent studies have made use of effective field theories to exploit in a systematic manner the hierarchy of energy scales that characterize the system. In the case of a quarkonium in a medium whose temperature is smaller than the typical momentum transfer in the bound state but larger than its energy, the suitable effective field theory is pNRQCD_HTL, where degrees of freedom with energy or momentum larger than the binding energy have been integrated out. Thermal effects are expected to break Poincar\'e invariance, which, at zero temperature, manifests itself in a set of exact relations between the matching coefficients of the effective field theory. In the paper, we evaluate the leading-order thermal corrections to the spin-orbit potentials of pNRQCD_HTL and show that Poincar\'e invariance is indeed violated., Comment: 17 page, 4 figures. Version published on JHEP

We present the complete next-to-next-to-leading-order calculation of the correlation function of two Polyakov loops for temperatures smaller than the inverse distance between the loops and larger than the Coulomb potential. We discuss the relationship of this correlator with the singlet and octet potentials which we obtain in an Effective Field Theory framework based on finite-temperature potential Non-Relativistic QCD, showing that the Polyakov loop correlator can be re-expressed, at the leading order in a multipole expansion, as a sum of singlet and octet contributions. We also revisit the calculation of the expectation value of the Polyakov loop at next-to-next-to-leading order., Comment: Presented at "Quark Confinement and the Hadron Spectrum IX - QCHS IX" (30 August - 3 September 2010, Madrid, Spain), to appear in the proceedings

We study the Polyakov loop and the correlator of two Polyakov loops at finite temperature in the weak-coupling regime. We calculate the Polyakov loop at order g^4. The calculation of the correlator of two Polyakov loops is performed at distances shorter than the inverse of the temperature and for electric screening masses larger than the Coulomb potential. In this regime, it is accurate up to order g^6. We also evaluate the Polyakov-loop correlator in an effective field theory framework that takes advantage of the hierarchy of energy scales in the problem and makes explicit the bound-state dynamics. In the effective field theory framework, we show that the Polyakov-loop correlator is at leading order in the multipole expansion the sum of a colour-singlet and a colour-octet quark-antiquark correlator, which are gauge invariant, and compute the corresponding colour-singlet and colour-octet free energies., Comment: 53 pages, 9 figures, version published in PRD

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., Comment: 25 pages, 2 figures

We study the three-quark static potential in perturbation theory in QCD. A complete next-to-leading order calculation is performed in the singlet, octets and decuplet channels and the potential exponentiation is demonstrated. The mixing of the octet representations is calculated. At next-to-next-to-leading order, the subset of diagrams producing three-body forces is identified in Coulomb gauge and its contribution to the potential calculated. Combining it with the contribution of the two-body forces, which may be extracted from the quark-antiquark static potential, we obtain the complete next-to-next-to-leading order three-quark static potential in the colour-singlet channel., Comment: 36 pages, 11 figures. v2: version published in Phys.Rev.D. v3: fixed numerical factor in Eq. (56) and following equations

In a framework that makes close contact with modern effective field theories for non-relativistic bound states at zero temperature, we study the real-time evolution of a static quark-antiquark pair in a medium of gluons and light quarks at finite temperature. For temperatures ranging from values larger to smaller than the inverse distance of the quark and antiquark, 1/r, and at short distances, we derive the potential between the two static sources, and calculate their energy and thermal decay width. Two mechanisms contribute to the thermal decay width: the imaginary part of the gluon self energy induced by the Landau damping phenomenon, and the quark-antiquark color singlet to color octet thermal break up. Parametrically, the first mechanism dominates for temperatures such that the Debye mass is larger than the binding energy, while the latter, which we quantify here for the first time, dominates for temperatures such that the Debye mass is smaller than the binding energy. If the Debye mass is of the same order as 1/r, our results are in agreement with a recent calculation of the static Wilson loop at finite temperature. For temperatures smaller than 1/r, we find new contributions to the potential, both real and imaginary, which may be relevant to understand the onset of heavy quarkonium dissociation in a thermal medium., Comment: 42 pages, 16 figures