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Jet quenching parameter in an expanding QCD plasma
http://cds.cern.ch/record/2625258
We study the phenomenon of transverse momentum broadening for a high-$p_T$ parton propagating through a weakly-coupled quark-gluon plasma undergoing boost-invariant longitudinal expansion. We propose a boost-invariant description for this phenomenon, in which the broadening refers to the angular variables $\eta$ (the pseudo-rapidity) and $\phi$ (the azimuthal angle). The jet quenching parameter $\hat{q}$ which enters this description depends upon the proper time alone. We furthermore consider radiative corrections to $\hat q$. As in the case of a static medium, we find potentially large corrections enhanced by a double logarithm. But unlike for the static medium, these corrections are now local in time: they depend upon the local (proper) time characterizing the expansion, and not upon the overall path length. We resum such corrections to all orders into a renormalized jet quenching parameter. The main effect of this resummation is to slow down the decrease of $\hat q$ with increasing proper time.Iancu, EdmondTaels, PieterWu, BinFri, 22 Jun 2018 04:47:02 GMT2018-06-19CERN-TH-2018-141http://cds.cern.ch/record/26252582018141$ZZ$ production at the LHC: NNLO predictions for $2\ell2\nu$ and $4\ell$ signatures
http://cds.cern.ch/record/2624793
We consider QCD radiative corrections to $ZZ$ production for all experimentally relevant leptonic processes. We report on a novel computation of next-to-next-to-leading-order (NNLO) corrections to the diboson signature with two charged leptons and missing transverse energy ($\ell\ell$+$E_T^{\rm miss}$). All relevant final states are considered: $\ell\ell\nu_\ell\nu_\ell$, $\ell\ell\nu_{\ell'}\nu_{\ell'}$ and $\ell\nu_{\ell}\ell'\nu_{\ell'}$. We also study processes with four charged leptons: $\ell\ell\ell\ell$ and $\ell\ell\ell'\ell'$. For the first time NNLO accuracy is achieved for a process mixing two double-resonant diboson topologies ($ZZ/W^+W^-\to\ell\ell\nu_\ell\nu_\ell$). We find good agreement with ATLAS data at 8 TeV. NNLO corrections are large (5-20% and more), and interference effects between $ZZ$ and $W^+W^-$ resonances turn out to be negligible in most cases.Kallweit, StefanWiesemann, MariusTue, 19 Jun 2018 11:55:04 GMT2018-06-15CERN-TH-2018-127http://cds.cern.ch/record/26247932018127Constraining anomalous gluon self-interactions at the LHC: a reappraisal
http://cds.cern.ch/record/2624791
Anomalous self-interactions of non-abelian gauge fields can be described by higher dimensional operators featuring gauge-invariant combinations of the field strengths. In the case of QCD, the gluon self-interactions start to be modified at dimension six by operators of the type $GGG$, with $G$ the gluon field strength tensor, possibly leading to deviations in all observables and measurements that probe strong interactions at very small distances. In this work we consider the sensitivity to the triple gluon operator of a series of observables at the LHC in di-jet, three- and multi-jet final states and heavy-quark production. We critically re-examine the robustness of long-standing as well as more recent proposals addressing issues such as the validity of the EFT expansion and the impact of higher order QCD corrections. Our results support the conclusion that multi-jet observables can reliably bound these anomalous interactions to the level that their impact on other key observables at the LHC, involving for example top quark and Higgs production, can be safely neglected. We also highlight the potential of using previously suggested angular observables in three-jet events at the LHC to further constrain these interactions.Hirschi, V.Maltoni, F.Tsinikos, I.Vryonidou, E.Tue, 19 Jun 2018 11:54:39 GMT2018-06-12CP3-18-35http://cds.cern.ch/record/26247911835Probing non-Gaussian Stochastic Gravitational Wave Backgrounds with LISA
http://cds.cern.ch/record/2622283
The stochastic gravitational wave background (SGWB) contains a wealth of information on astrophysical and cosmological processes. A major challenge of upcoming years will be to extract the information contained in this background and to disentangle the contributions of different sources. In this paper we provide the formalism to extract, from the correlation of three signals in the Laser Interferometer Space Antenna (LISA), information about the tensor three-point function, which characterizes the non-Gaussian properties of the SGWB. Compared to the two-point function, the SGWB three-point function has a richer dependence on the gravitational wave momenta and chiralities, and a larger number of signal channels. It can be used therefore as a powerful discriminator between different models. We provide LISA's response functions to a general SGWB three-point function. As examples, we study in full detail the cases of an equilateral and squeezed SGWB bispectra, and provide the explicit form of the response functions, ready to be convoluted with any theoretical prediction of the bispectrum to obtain the observable signal. We further derive the optimal estimator to compute the signal-to-noise ratio. Our formalism covers general shapes of non-Gaussianity, and can be extended straightaway to other detector geometries. Finally, we provide a short overview of models of the early universe that can give rise to non-Gaussian SGWB.Bartolo, NicolaDomcke, ValerieFigueroa, Daniel G.Garcia-Bellido, JuanPeloso, MarcoPieroni, MauroRicciardone, AngeloSakellariadou, MairiSorbo, LorenzoTasinato, GianmassimoFri, 08 Jun 2018 06:25:41 GMT2018-06-07UMN-TH/3720-18http://cds.cern.ch/record/2622283TH/372018Hadronic and New Physics Contributions to B -> K* l+ l-
http://cds.cern.ch/record/2622282
The significance of the observed tensions in the angular observables in B -> K* mu+ mu- are dependent on the theory estimation of the hadronic contributions to these decays. Therefore, we discuss in detail the various available approaches for taking into account the long-distance hadronic effects and examine how the different estimations of these contributions result in distinct significance of the new physics interpretation of the observed anomalies. Furthermore, besides the various theory estimations of the non-factorisable contributions we consider a general parameterisation which is fully consistent with the analyticity structure of the amplitudes. We make a statistical comparison to find whether the most favoured explanation of the anomalies is new physics or underestimated hadronic effects within this general parametrisation. Moreover, assuming the source of the anomalies to be new physics, there is a priori no reason to believe that - in the effective field theory language - only one type of operator is responsible for the tensions. We thus perform a global fit where all the Wilson coefficients which can effectively receive new physics contributions are considered, allowing for lepton flavour universality breaking effects as well as contributions from chirality flipped and scalar and pseudoscalar operators.Arbey, A.Hurth, T.Mahmoudi, F.Neshatpour, S.Fri, 08 Jun 2018 06:25:31 GMT2018-06-07CERN-TH-2018-134http://cds.cern.ch/record/26222822018134Dynamics of Finite-Temperature CFTs from OPE Inversion Formulas
http://cds.cern.ch/record/2622281
We apply the OPE inversion formula to thermal two-point functions of bosonic and fermionic CFTs in general odd dimensions. This allows us to analyze in detail the operator spectrum of these theories. We find that nontrivial thermal CFTs arise when the thermal mass satisfies an algebraic transcendental equation that ensures the absence of an infinite set of operators from the spectrum. The solutions of these gap equations for general odd dimensions are in general complex numbers and follow a particular pattern. We argue that this pattern unveils the large-$N$ vacuum structure of the corresponding theories at zero temperature.Petkou, Anastasios C.Stergiou, AndreasFri, 08 Jun 2018 06:25:31 GMT2018-06-06CERN-TH-2018-132http://cds.cern.ch/record/26222812018132Post-inflationary thermal histories and the refractive index of relic gravitons
http://cds.cern.ch/record/2622279
We investigate the impact of the post-inflationary thermal histories on the cosmic graviton spectrum caused by the inflationary variation of their refractive index. Depending on the frequency band, the spectral energy distribution can be mildly red, blue or even violet. Wide portions of the parameter space lead to potentially relevant signals both in the audio range (probed by the advanced generation of terrestrial interferometers) and in the mHz band (where space-borne detectors could be operational within the incoming score year). The description of the refractive index in conformally related frames is clarified.Giovannini, MassimoFri, 08 Jun 2018 06:25:02 GMT2018-06-05CERN-TH-2018-122-http://cds.cern.ch/record/2622279122Next-to-leading order electroweak corrections to off-shell WWW production at the LHC
http://cds.cern.ch/record/2621441
Triboson processes allow for a measurement of the triple and quartic couplings of the Standard Model gauge bosons, which can be used to constrain anomalous gauge couplings. In this paper we calculate the next-to-leading order electroweak corrections to fully off-shell $W^-W^+W^+$ production, namely the production of a $\ell_1^-\ell_2^+\ell_3^+\bar{\nu}_{\ell_1}\nu_{\ell_2}\nu_{\ell_3}$ final state with ($\ell_i=e,\mu$), including all triple, double, single and non resonant topologies and interferences of diagrams with all different vector boson ($W,Z,\gamma$) intermediate states. We find large cancellations of the electroweak correction to the $q\bar{q}$-induced channel, which includes the exchange of virtual electroweak gauge bosons, and photon-induced jet radiation processes. This accidental compensation is found to be strongly phase space and observable dependent. The resulting corrections in a suitably defined fiducial region thus amount to $-2.0\%$, but rise rapidly for other observables.Schönherr, MarekMon, 04 Jun 2018 05:22:49 GMT2018-06-01CERN-TH-2018-129http://cds.cern.ch/record/26214412018129Spin-four N=7 W-Supergravity: S-fold and Double Copy Construction
http://cds.cern.ch/record/2320399
In the present investigation we consider the possibility of having new massive, higher spin W-supergravity theories, which do not exist as four-dimensional perturbative models. These theories are based on a double copy construction of two supersymmetric field theories, where at least one factor is given by a N=3 field theory, which is a non-perturbative S-fold of N=4 super Yang-Mills theory. In this way, we can obtain as S-folds a new N=7 (corresponding to 28 supercharges) W-supergravity and its N=7 W-superstring counterpart, which both do not exist as four-dimensional perturbative models with an (effective) Langrangian description. The resulting field resp. string theory does not contain any massless states, but instead a massive higher spin-four supermultiplet of the N=7 supersymmetry algebra. Furthermore we also construct a four-dimensional heterotic S-fold with N=3 supersymmetry. It again does not exist as perturbative heterotic string model and can be considered as the heterotic counterpart of the N=3 superconformal field theories, which were previously constructed in the context of type I orientfold models.Ferrara, SergioLüst, DieterMon, 28 May 2018 05:20:37 GMT2018-05-25CERN-TH-2018-112http://cds.cern.ch/record/23203992018112NNLOPS accurate predictions for $W^+W^-$ production
http://cds.cern.ch/record/2320397
We present novel predictions for the production of $W^+W^-$ pairs in hadron collisions that are next-to-next-to-leading order accurate and consistently matched to a parton shower (NNLOPS). All diagrams that lead to the process $pp\to e^- \bar \nu_e\;\mu^+\nu_\mu+X$ are taken into account, thereby including spin correlations and off-shell effects. For the first time full NNLOPS accuracy is achieved for a $2\to 4$ process. We find good agreement, at the 1$\sigma$ level, with the $W^+W^-$ rates measured by ATLAS and CMS. The importance of NNLOPS predictions is evident from differential distributions sensitive to soft-gluon effects and from the large impact ($10$% and more) of including next-to-next-to-leading order corrections on top of MiNLO. We define a charge asymmetry for the $W$ bosons and the leptons in $W^+W^-$ production at the LHC, which is sensitive to the $W$ polarizations and hence can be used as a probe of new physics.Re, EmanueleWiesemann, MariusZanderighi, GiuliaMon, 28 May 2018 05:20:20 GMT2018-05-24CERN-TH/2018-114http://cds.cern.ch/record/2320397TH/2018114Consistent Conformal Extensions of the Standard Model
http://cds.cern.ch/record/2320061
The question of whether classically conformal modifications of the standard model are consistent with experimental obervations has recently been subject to renewed interest. The method of Gildener and Weinberg provides a natural framework for the study of the effective potential of the resulting multi-scalar standard model extensions. This approach relies on the assumption of the ordinary loop hierarchy $\lambda_\text{s} \sim g^2_\text{g}$ of scalar and gauge couplings. On the other hand, Andreassen, Frost and Schwartz recently argued that in the (single-scalar) standard model, gauge invariant results require the consistent scaling $\lambda_\text{s} \sim g^4_\text{g}$. In the present paper we contrast these two hierarchy assumptions and illustrate the differences in the phenomenological predictions of minimal conformal extensions of the standard model.Loebbert, FlorianMiczajka, JulianPlefka, JanFri, 25 May 2018 05:20:29 GMT2018-05-24HU-EP-18/16http://cds.cern.ch/record/2320061EP18/16Uncertainties in WIMP Dark Matter Scattering Revisited
http://cds.cern.ch/record/2320060
We revisit the uncertainties in the calculation of spin-independent scattering matrix elements for the scattering of WIMP dark matter particles on nuclear matter. In addition to discussing the uncertainties due to limitations in our knowledge of the nucleonic matrix elements of the light quark scalar densities < N |{\bar u} u, {\bar d} d, {\bar s} s| N>, we also discuss the importances of heavy quark scalar densities < N |{\bar c} c, {\bar b} b, {\bar t} t| N >, and comment on uncertainties in quark mass ratios. We analyze estimates of the light-quark densities made over the past decade using lattice calculations and/or phenomenological inputs. We find an uncertainty in the combination < N |{\bar u} u + {\bar d} d | N > that is larger than has been assumed in some phenomenological analyses, and a range of < N |{\bar s} s| N > that is smaller but compatible with earlier estimates. We also analyze the importance of the {\cal O}(\alpha_s^3) calculations of the heavy-quark matrix elements that are now available, which provide an important refinement of the calculation of the spin-independent scattering cross section. We use for illustration a benchmark CMSSM point in the focus-point region that is compatible with the limits from LHC and other searches.Ellis, JohnNagata, NatsumiOlive, Keith A.Fri, 25 May 2018 05:20:26 GMT2018-05-24KCL-PH-TH-2018-19http://cds.cern.ch/record/2320060201819Comments on rigid and local supercurrents in ${\cal N}=1$ minimal Supergravity
http://cds.cern.ch/record/2319845
We discuss local supercurrents as sources of the super-Einstein equations in the superconformal approach in the old and new minimal (auxiliary fields) formulation. Modifications of the Ward identity giving the covariant divergence of the Einstein multiplet are considered in presence of a Fayet-Iliopoulos term. Curvature multiplets can be used as alternative to the gravitino variation in the search for rigid supersymmetric curved backgrounds.Ferrara, SergioSamsonyan, MarineTournoy, MagnusVan Proeyen, AntoineThu, 24 May 2018 06:05:57 GMT2018-05-23CERN-TH-2018-071http://cds.cern.ch/record/23198452018071Does shape matter? v_2 vs eccentricity in small x gluon production
http://cds.cern.ch/record/2319843
We study analytically and numerically effects of spatial eccentricity of the projectile shape on the second flow harmonic in inclusive gluon production in p-A collisions in the CGC framework. Keeping the collision area fixed, we find that the two quantities are anti-correlated.Kovner, AlexSkokov, Vladimir V.Thu, 24 May 2018 06:05:15 GMT2018-05-23CERN-TH-2018-077http://cds.cern.ch/record/23198432018077Bose enhancement, the Liouville effective action and the high multiplicity tail in p-A collisions
http://cds.cern.ch/record/2319842
In the framework of dense-dilute CGC approach we study fluctuations in the multiplicity of produced particles in p-A collisions. We show that the leading effect that drives the fluctuations is the Bose enhancement of gluons in the proton wave function. We explicitly calculate the moment generating function that resums the effects of Bose enhancement. We show that it can be understood in terms of the Liouville effective action for the composite field which is identified with the fluctuating density, or saturation momentum of the proton. The resulting probability distribution turns out to be very close to the gamma-distribution. We also calculate the first correction to this distribution which is due to pairwise Hanbury Brown-Twiss correlations of produced gluons.Kovner, AlexSkokov, Vladimir V.Thu, 24 May 2018 06:05:13 GMT2018-05-23CERN-TH-2018-101http://cds.cern.ch/record/23198422018101Blue and violet graviton spectra from a dynamical refractive index
http://cds.cern.ch/record/2319226
We show that the spectral energy distribution of relic gravitons mildly increases for frequencies smaller than the $\mu$Hz and then flattens out whenever the refractive index of the tensor modes is dynamical during a quasi-de Sitter stage of expansion. For a conventional thermal history the high-frequency plateau ranges between the mHz and the audio band but it is supplemented by a spike in the GHz region if a stiff post-inflationary phase precedes the standard radiation-dominated epoch. Even though the slope is blue at intermediate frequencies, it may become violet in the MHz window. For a variety of post-inflationary histories, including the conventional one, a dynamical index of refraction leads to a potentially detectable spectral energy density in the kHz and in the mHz regions while all the relevant phenomenological constraints are concurrently satisfied.Giovannini, MassimoTue, 22 May 2018 05:18:42 GMT2018-05-21arXiv:1805.08142http://cds.cern.ch/record/2319226['arXiv:1805.08142']arXiv:1805.08142Mass-improvement of the vector current in three-flavor QCD
http://cds.cern.ch/record/2319225
We determine two improvement coefficients which are relevant to cancel mass-dependent cutoff effects in correlation functions with operator insertions of the non-singlet local QCD vector current. This determination is based on degenerate three-flavor QCD simulations of non-perturbatively O(a) improved Wilson fermions with tree-level improved gauge action. Employing a very robust strategy that has been pioneered in the quenched approximation leads to an accurate estimate of a counterterm cancelling dynamical quark cutoff effects linear in the trace of the quark mass matrix. To our knowledge this is the first time that such an effect has been determined systematically with large significance.Fritzsch, PatrickTue, 22 May 2018 05:18:38 GMT2018-05-18CERN-TH-2018-119http://cds.cern.ch/record/23192252018119A Realistic $U(2)$ Model of Flavor
http://cds.cern.ch/record/2319086
We propose a simple $U(2)$ model of flavor compatible with an $SU(5)$ GUT structure. All hierarchies in fermion masses and mixings arise from powers of two small parameters that control the $U(2)$ breaking. In contrast to previous $U(2)$ models this setup can be realized without supersymmetry and provides an excellent fit to all SM flavor observables including neutrinos. We also consider a variant of this model based on a $D_6 \times U(1)_F$ flavor symmetry, which closely resembles the $U(2)$ structure, but allows for Majorana neutrino masses from the Weinberg operator. Remarkably, in this case one naturally obtains large mixing in the lepton sector from small mixing in the quark sector. The model also offers a natural option for addressing the Strong CP Problem and Dark Matter by identifying the Goldstone boson of the $U(1)_F$ factor as the QCD axion.Linster, MatthiasZiegler, RobertMon, 21 May 2018 05:43:23 GMT2018-05-18CERN-TH-2018-121http://cds.cern.ch/record/23190862018121Universal Imprints of a Pseudo-Nambu-Goldstone Higgs Boson
http://cds.cern.ch/record/2318949
A large class of models addressing the electroweak naturalness problem postulates the existence of new spontaneously broken global symmetries above the weak scale. The Higgs boson arises as a pseudo-Nambu-Goldstone boson (pNGB) whose interactions are nonlinear due to the presence of de- generate vacua. We argue that, once the normalization of the pNGB decay constant f is determined, the Higgs nonlinear interactions in the gauge sector are universal in the infrared and independent of the symmetry breaking pattern G/H, even after integrating out heavy composite resonances. We propose a set of "universal relations" in Higgs couplings with electroweak gauge bosons and in triple gauge boson couplings, which are unique predictions of the universal nonlinearity. Experimental measurements of these relations would serve as the litmus test of a pNGB Higgs boson.Liu, DaLow, IanYin, ZheweiSat, 19 May 2018 21:27:10 GMT2018-05-01arXiv:1805.00489http://cds.cern.ch/record/2318949['arXiv:1805.00489']arXiv:1805.00489Quantum diffusion beyond slow-roll: implications for primordial black-hole production
http://cds.cern.ch/record/2318786
Primordial black-holes (PBH) can be produced in single-field models of inflation with a quasi-inflection point in the potential. In these models, a large production of PBHs requires a deviation from the slow-roll (SR) trajectory. In turn, this SR violation can produce an exponential growth of quantum fluctuations. We study the back-reaction of these quantum modes on the inflationary dynamics using stochastic inflation in the Hamilton-Jacobi formalism. We develop a methodology to solve quantum diffusion beyond SR in terms of the statistical moments of the probability distribution. We apply these techniques to a toy model potential with a quasi-inflection point. We find that there is an enhancement of the power spectrum due to the dominance of the stochastic noise in the phase beyond SR. Moreover, non-Gaussian corrections become as well relevant with a large positive kurtosis. Altogether, this produces a significant boost of PBH production. We discuss how our results extend to other single-field models with similar dynamics. We conclude that the abundance of PBHs in this class of models should be revisited including quantum diffusion.Ezquiaga, Jose MaríaGarcía-Bellido, JuanFri, 18 May 2018 06:24:08 GMT2018-05-17IFT-UAM/CSIC-18-051http://cds.cern.ch/record/231878618051On the interior geometry of a typical black hole microstate
http://cds.cern.ch/record/2318541
We argue that the region behind the horizon of a one-sided black hole can be probed by an analogue of the double-trace deformation protocol of Gao-Jafferis-Wall. This is achieved via a deformation of the CFT Hamiltonian by a term of the form ${\cal O} \widetilde{\cal O}$, where $\widetilde{\cal O}$ denote the state-dependent "mirror operators". We argue that this deformation creates negative energy shockwaves in the bulk, which allow particles inside the horizon to escape and to get directly detected in the CFT. This provides evidence for the smoothness of the horizon of black holes dual to typical states. We argue that the mirror operators allow us to perform an analogue of the Hayden-Preskill decoding protocol. Our claims rely on a technical conjecture about the chaotic behavior of out-of-time-order correlators on typical pure states at scrambling time.De Boer, JanLokhande, Sagar F.Verlinde, ErikVan Breukelen, RikPapadodimas, KyriakosThu, 17 May 2018 05:35:56 GMT2018-04-27arXiv:1804.10580http://cds.cern.ch/record/2318541['arXiv:1804.10580']arXiv:1804.10580Fiducial distributions in Higgs and Drell-Yan production at N$^3$LL+NNLO
http://cds.cern.ch/record/2318419
The perturbative description of certain differential distributions across a wide kinematic range requires the matching of fixed-order perturbation theory with resummation of large logarithmic corrections to all orders. We present precise matched predictions for transverse-momentum distributions in Higgs boson (H) and Drell-Yan pair (DY) production as well as for the closely related ${\phi^{*}_\eta}$ distribution at the LHC. The calculation is exclusive in the Born kinematics, and allows for arbitrary fiducial selection cuts on the decay products of the colour singlets, which is of primary relevance for experimental analyses. Our predictions feature very small residual scale uncertainties and display a good convergence of the perturbative series. A comparison of the predictions for DY observables to experimental data at 8 TeV shows a very good agreement within the quoted errors.Bizoń, WojciechChen, XuanGehrmann-De Ridder, AudeGehrmann, ThomasGlover, NigelHuss, AlexanderMonni, Pier FrancescoRe, EmanueleRottoli, LucaTorrielli, PaoloWed, 16 May 2018 06:00:40 GMT2018-05-15CERN-TH-2018-105http://cds.cern.ch/record/23184192018105The exact $C$-function in integrable $\lambda$-deformed theories
http://cds.cern.ch/record/2317222
By employing CFT techniques, we show how to compute in the context of \lambda-deformations of current algebras and coset CFTs the exact in the deformation parameters C-function for a wide class of integrable theories that interpolate between a UV and an IR point. We explicitly consider RG flows for integrable deformations of left-right asymmetric current algebras and coset CFTs. In all cases, the derived exact C-functions obey all the properties asserted by Zamolodchikov's c-theorem in two-dimensions.Georgiou, GeorgePanopoulos, PantelisSagkrioti, EftychiaSfetsos, KonstantinosSiampos, KonstantinosFri, 11 May 2018 05:31:24 GMT2018-05-09CERN-TH-2018-104http://cds.cern.ch/record/23172222018104Kinetic transport is needed to reliably extract shear viscosity from pA and AA data
http://cds.cern.ch/record/2317221
The azimuthal anisotropies $v_n$ of particle spectra measured in proton-nucleus (pA) and nucleus-nucleus (AA) collisions play a key role in constraining QCD matter properties like the shear viscosity over entropy density ratio $\eta/s$. Here, we compare calculations of $v_n$'s from viscous fluid dynamics and from kinetic transport which start both from the same initial conditions and which implement the same matter properties. We observe that both approaches lead to parametrically different $\eta/s$-dependencies of the elliptic anisotropy $v_2$ and they may thus lead to quantitatively different results for the phenomenologically inferred value of $\eta/s$. The parametric differences can be traced to the boost-invariant longitudinal expansion of pA and AA collisions which induces in fluid dynamic results of the $\eta/s$-dependence of $v_2$ a dominant sensitivity on the initial conditions. Transport theory is free of this problem and it accounts for the order of magnitude of experimentally observed signal strengths $v_n$ with sizeable mean free path.Kurkela, AleksiWiedemann, Urs AchimWu, BinFri, 11 May 2018 05:31:21 GMT2018-05-10CERN-TH-2018-115http://cds.cern.ch/record/23172212018115Lattice QCD study of the $H$ dibaryon using hexaquark and two-baryon interpolators
http://cds.cern.ch/record/2317220
We present a lattice QCD spectroscopy study in the isospin singlet, strangeness $-2$ sectors relevant for the conjectured $H$ dibaryon. We employ both hexaquark and two-baryon interpolating operators to isolate the ground state in the rest frame and in moving frames. Calculations are performed using two flavors of O($a$)-improved Wilson fermions and a quenched strange quark. Our initial point-source method for constructing correlators does not allow for two-baryon operators at the source; nevertheless, results from using these operators at the sink indicate that they provide an improved overlap onto the ground state in comparison with the hexaquark operators. We also present results, in the rest frame, using a second method based on distillation to compute a hermitian matrix of correlators with two-baryon operators at both the source and the sink. This method yields a much more precise and reliable determination of the ground-state energy. In the flavor-SU(3) symmetric case, we apply L\"uscher's finite-volume quantization condition to the rest-frame and moving-frame energy levels to determine the $S$-wave scattering phase shift, near and below the two-particle threshold. For a pion mass of 960 MeV, we find that there exists a bound $H$ dibaryon with binding energy ${\Delta}E=(19\pm10)$ MeV. In the 27-plet (dineutron) sector, the finite-volume analysis suggests that the existence of a bound state is unlikely.Francis, A.Green, J.R.Junnarkar, P.M.Miao, Ch.Rae, T.D.Wittig, H.Fri, 11 May 2018 05:31:02 GMT2018-05-10CERN-TH-2018-098http://cds.cern.ch/record/23172202018098