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Nuno Cardoso

Publications and source records attributed to Nuno Cardoso.

At least 19 recordsLinked to original sources
arXiv2024

Tricriticality in 4D U(1) Lattice Gauge Theory

The 4D compact U(1) gauge theory has a well-established phase transition between a confining and a Coulomb phase. In this paper, we revisit this model using state-of-the-art Monte Carlo simulations on anisotropic lattices. We map out the coupling-temperature phase diagram, and determine the location of the tricritical point, $T/K_0 \simeq 0.19$, below which the first-order transition is observed. We find the critical exponents of the high-temperature second-order transition to be compatible with those of the 3-dimensional $O(2)$ model. Our results at higher temperatures can be compared with literature results and are consistent with them. Surprisingly, below $T/K_0 \simeq 0.05$ we find strong indications of a second tricritical point where the first-order transition becomes continuous. These results suggest an unexpected second-order phase transition extending down to zero temperature, contrary to the prevailing consensus. If confirmed, these findings reopen the question of the detailed characterization of the transition including a suitable field theory description.

hep-lat↗
arXiv2023

Eight very excited spectra and one possible axion in SU(3) lattice gauge theory

We compute the spectra of flux tubes formed between a static quark antiquark pair up to a significant number of excitations and for eight symmetries of the flux tubes, up to $Δ_u$, using pure $SU(3)$ gauge lattice QCD in 3+1 dimensions. To accomplish this goal, we use a large set of appropriate operators, an anisotropic tadpole improved action, smearing techniques, and solve a generalized eigenvalue problem. Moreover, we compare our results with the Nambu-Goto string model to evaluate possible tensions which could be a signal for novel phenomena. Especially, we provide evidence for the coupling of a massive particle, say an axion, to the $Σ_g^-$, $Σ_u^-$, and $Σ_u^{-*}$ flux tube with approximate masses $ 2.25\sqrtσ$, $1.85\sqrtσ$, $3.30\sqrtσ$, respectively.

hep-lat↗
arXiv2022

Study of $I=0$ bottomonium bound states and resonances based on lattice QCD static potentials

We investigate $I = 0$ bottomonium bound states and resonances in S, P, D and F waves using lattice QCD static-static-light-light potentials. We consider five coupled channels, one confined quarkonium and four open $B^{(*)}\bar{B}^{(*)}$ and $B^{(*)}_s\bar{B}^{(*)}_s$ meson-meson channels and use the Born-Oppenheimer approximation and the emergent wave method to compute poles of the T matrix. We discuss results for masses and decay widths and compare them to existing experimental results. Moreover, we determine the quarkonium and meson-meson composition of these states to clarify, whether they are ordinary quarkonium or should rather be interpreted as tetraquarks.

hep-lat↗
arXiv2022

Eight spectra of very excited flux tubes in $SU(3)$ gauge theory

We compute the spectra of flux tubes formed between a static quark antiquark pair up to a significant number of excitations and for eight symmetries of the flux tubes, up to $Δ_u$, using pure $SU(3)$ gauge lattice QCD in $3+1$ dimensions. To accomplish this goal, we use a large set of appropriate operators, an anisotropic tadpole improved action, smearing techniques, and solve a generalized eigenvalue problem. Moreover, we compare our results with the Nambu-Goto string model to evaluate possible tensions which could be a signal for novel phenomena.

hep-lat↗
arXiv2022

Study of $I=0$ bottomonium bound states and resonances in $S$, $P$, $D$ and $F$ waves with lattice QCD static-static-light-light potentials

In this paper we study $I = 0$ bottomonium in $S$, $P$, $D$ and $F$ waves considering five coupled channels, one confined quarkonium and four open $B^{(*)} \bar B^{(*)}$ and $B_s^{(*)} \bar B_s^{(*)}$ meson-meson channels. To this end we use and extend a recently developed novel approach utilizing lattice QCD string breaking potentials for the study of quarkonium bound states and resonances. This approach is based on the Born Oppenheimer approximation and the unitary emergent wave method and allows to compute the poles of the $\mbox{T}$ matrix. We compare our results to existing experimental results for $I = 0$ bottomonium and discuss masses, decay widths and the assignment of angular momentum quantum numbers. Moreover, we determine the quarkonium and meson-meson composition of these states to clarify, which of them are ordinary quarkonium, and which of them should rather be interpreted as tetraquarks.

hep-lat↗
arXiv2022

Bottomonium resonances from lattice QCD static-static-light-light potentials

We study $I=0$ quarkonium resonances decaying into pairs of heavy-light mesons using static-static-light-light potentials from lattice QCD. To this end, we solve a coupled channel Schrödinger equation with a confined quarkonium channel and channels with a heavy-light meson pair to compute phase shifts and $\mbox{T}$ matrix poles for the lightest decay channel. We discuss our results for $S$, $P$, $D$ and $F$ wave states in the context of corresponding experimental results, in particular for $Υ(10753)$ and $Υ(10860)$.

hep-lat↗
arXiv2022

Computation of the quarkonium and meson-meson composition of the $Υ(nS)$ states and of the new $Υ(10753)$ Belle resonance from lattice QCD static potentials

We compute the composition of the bottomonium $Υ(nS)$ states (including $Υ(10860)$) and the new $Υ(10753)$ resonance reported by Belle in terms of quarkonium and meson-meson components. We use a recently developed novel approach utilizing lattice QCD string breaking potentials for the study of resonances. This approach is based on the Born Oppenheimer approximation and the unitary emergent wave method and allows to compute the poles of the $\mbox{S}$ matrix. We focus on $I=0$ bottomonium $S$ wave bound states and resonances, where the Schrödinger equation is a set of coupled differential equations. One of the channels corresponds to a confined heavy quark-antiquark pair $\bar b b$, the others to pairs of heavy-light mesons. In a previous study only one meson-meson channel $\bar{B}^{(\ast)} B^{(\ast)}$ was considered. Now we also include the closed strangeness channel $\bar{B}_s^{(\ast)} B_s^{(\ast)}$ extending our formalism significantly to have a more realistic description of bottomonium. We confirm the new Belle resonance $Υ(10753)$ as a dynamical meson-meson resonance with around $85 \%$ meson-meson content. Moreover, we identify $Υ(4S)$ and $Υ(10860)$ as states with both sizable quarkonium and meson-meson contents. With these results we contribute to the clarification of ongoing controversies in the vector bottomonium spectrum.

hep-lat↗
arXiv2021

Highly excited pure gauge SU(3) flux tubes

Flux tube spectra are expected to have full towers of levels due to the quantization of the string vibrations. We study a spectrum of flux tubes with static quark and antiquark sources with pure gauge $SU(3)$ lattice QCD in 3+1 dimensions up to a significant number of excitations. To go high in the spectrum, we specialize in the most symmetric case $Σ_g^+$, use a large set of operators, solve the generalized eigenvalue and compare different lattice QCD gauge actions and anisotropies.

hep-lat↗
arXiv2020

From string breaking to quarkonium spectrum

We present a preliminary computation of potentials between two static quarks in $n_f=2$ QCD with O(a) improved Wilson fermions. We explore different smearing choices (HYP, HYP2 and APE) and their effect on the signal to noise ratio in the computed static potentials. This is a part of a larger effort concerning, at first, a precise computation of the QCD string breaking parameters and their subsequent utilization for the recent approach based on Born-Oppenheimer approximation (Bicudo et al. 2020 \cite{Bicudo:2019ymo}) to study quarkonium resonances and bound states.

hep-lat↗
arXiv2020

Bottomonium resonances with $I = 0$ from lattice QCD correlation functions with static and light quarks

We discuss, how to study $I = 0$ quarkonium resonances decaying into pairs of heavy-light mesons using static potentials from lattice QCD. These static potentials can be obtained from a set of correlation functions containing both static and light quarks. As a proof of concept we focus on bottomonium with relative orbital angular momentum $L = 0$ of the $\bar{b} b$ pair corresponding to $J^{P C} = 0^{- +}$ and $J^{P C} = 1^{- -}$. We use static potentials from an existing lattice QCD string breaking study and compute phase shifts and $\mbox{T}$ matrix poles for the lightest heavy-light meson-meson decay channel. We discuss our results in the context of corresponding experimental results, in particular for $Υ(10860)$ and $Υ(11020)$.

hep-lat↗
arXiv2019

Exploring the tension between nature and the Standard Model: the muon g-2

Anomalous magnetic moment of the muon (muon g-2) is one of the most precisely measured quantities in particle physics. At the same time, it can be evaluated in the Standard Model with an unprecedented accuracy. The Muon g-2 experiment at Fermilab has started the major data collection and the aimed four-fold increase in precision will shed light on the current discrepancy between the theory prediction and the measured value. This renders a comparable improvement of the precision in the SM theory an essential ingredient in order to fully exploit the expected increase of precision in experimental results. For all these reasons, the muon g-2 is considered to be a great testing ground for new physics. Hadronic contributions are the dominant sources of uncertainty in the theoretical prediction of the muon g-2. A reciprocal effort to a precise determination of the leading hadronic contribution to the muon g-2 using lattice gauge theories is a direct measurement of the hadronic contributions to the running of the fine structure constant recently proposed by the MUonE experiment. A hybrid strategy including both experimental and lattice data sets is expected to give an independent check of the dispersive results from $e^+e^-$ annihilation, which dominate the current world average.

hep-lat↗
arXiv2018

Colour fields of the quark-antiquark excited flux tube

We present colour field density profiles for some of the first SU(3) gluonic excitations of the flux tube in the presence of a static quark-antiquark pair. The results are obtained from a large set of gluonic operators.

hep-lat↗
arXiv2017

Flux tubes at Finite Temperature

In this work, we show the flux tubes of the quark-antiquark and quark-quark at finite temperature for SU(3) Lattice QCD. The chromomagnetic and chromoelectric fields are calculated above and below the phase transition.

hep-lat↗
arXiv2016

Flux tubes at Finite Temperature

We show the flux tubes produced by static quark-antiquark, quark-quark and quark-gluon charges at finite temperature. The sources are placed in the lattice with fundamental and adjoint Polyakov loops. We compute the square densities of the chromomagnetic and chromoelectric fields above and below the phase transition. Our results are gauge invariant and produced in pure gauge SU(3). The codes are written in CUDA and the computations are performed with GPUs.

hep-lat↗
arXiv2015

SOSpin, a C++ library for Yukawa decomposition in SO(2N) models

We present in this paper the SOSpin library, which calculates an analytic decomposition of the Yukawa interactions invariant under any SO(2N) group in terms of an SU(N) basis. We make use of the oscillator expansion formalism, where the SO(2N) spinor representations are expressed in terms of creation and annihilation operators of a Grassmann algebra. These noncommutative operators and their products are simulated in SOSpin through the implementation of doubly-linked-list data structures. These data structures were determinant to achieve a higher performance in the simplification of large products of creation and annihilation operators. We illustrate the use of our library with complete examples of how to decompose Yukawa terms invariant under SO(2N) in terms of SU(N) degrees of freedom for N=2 and 5. We further demonstrate, with an example for SO(4), that higher dimensional field-operator terms can also be processed with our library. Finally, we describe the functions available in SOSpin that are made to simplify the writing of spinors and their interactions specifically for SO(10) models.

hep-ph↗
arXiv2015

Gauge fixing and the gluon propagator in renormalizable xi gauges

Covariant $R_ξ$ gauge fixing is notoriously difficult for large lattice volumes, large $ξ$ and small $N_c$. We thoroughly test different convergence techniques, which allows the gauge fixing of lattice configurations with a total volume of (3.25 fm)$^4$, up to $ξ=0.5$. We are able to study the gluon propagator in the infrared region and its dependence on the gauge fixing parameter $ξ$. As expected, the longitudinal gluon dressing functions stay constant at their tree-level value $ξ$. Similar to the Landau gauge, the transverse $R_ξ$ gauge gluon propagators saturate at a non-vanishing value in the deep infrared for all values of $ξ$ studied. We compare with very recent continuum studies and perform a simple analysis of the found saturation with a dynamically generated effective gluon mass.

hep-lat↗
arXiv2015

Coulomb and Landau Gauge Fixing in GPUs using CUDA and MILC

In this work, we present the GPU implementation of the overrelaxation and steepest descent method with Fourier acceleration methods for Laudau and Coulomb gauge fixing using CUDA for SU(N) with N>2. A multi-GPU implementation of the overrelaxation method is also presented using MPI and CUDA. The GPU performance was measured on BlueWaters and compared against the gauge fixing of the CPU MILC code.

hep-lat↗