New articles on High Energy Physics - Lattice

[1] 2407.15422

Lattice study of SU(2) gauge theory coupled to four adjoint Higgs fields

Gauge theories with matter fields in various representations play an important role in different branches of physics. Recently, it was proposed that several aspects of the interesting pseudogap phase of cuprate superconductors near optimal doping may be explained by an emergent $SU(2)$ gauge symmetry. Around the transition with positive hole-doping, one can construct a $(2+1)-$dimensional $SU(2)$ gauge theory coupled to four adjoint scalar fields which gives rise to a rich phase diagram with a myriad of phases having different broken symmetries. We study the phase diagram of this model on the Euclidean lattice using the Hybrid Monte Carlo algorithm. We find the existence of multiple broken phases as predicted by previous mean field studies. Depending on the quartic couplings, the $SU(2)$ gauge symmetry is broken down either to $U(1)$ or $\mathbb{Z}_2$ in the perturbative description of the model. We further study the confinement-deconfinement transition in this theory, and find that both the broken phases are deconfining. However, there exists a marked difference in the behavior of the Polyakov loop between the two phases.

[2] 2407.14548

Triply charm and bottom tetraquarks in a constituent quark model

Recently, the singly, doubly and fully charmed tetraquark candidates, $T_{c\bar{s}}(2900)$, $T^+_{cc}(3875)$ and $X(6900)$ are experimentally reported by the LHCb collaboration. Hence, it is quite necessary to implement a theoretical investigation on the triply heavy tetrquarks. In this study, the S-wave triply charm and bottom tetraquarks, $\bar{Q}Q\bar{q}Q$ $(q=u,\,d,\,s;\,Q=c,\,b)$, with spin-parity $J^P=0^+$, $1^+$ and $2^+$, isospin $I=0$ and $\frac{1}{2}$ are systematically studied in a constituent quark model. Particularly, a complete S-wave tetraquark configurations, which include the meson-meson, diquark-antidiquark and K-type arrangements of quarks, along with all allowed color structures, are comprehensively considered. A high accuracy and efficient computational approach, the Gaussian expansion method (GEM), in cooperation with a powerful complex-scaling method (CSM), which is quite ingenious in dealing with the bound and resonant state of a multiquark system simultaneously, are adopted in solving the complex scaled Schr\"odinger equation. This theoretical framework has already been successfully applied in various tetra- and penta-quark systems. Bound state of triply heavy tetraquark system is unavailable in our study, nevertheless, in a fully coupled-channel calculation by the CSM, several narrow resonances are found in each $I(J^P)$ quantum states of the charm and bottom sector. In particular, triply charm and bottom tetraquark resonances are obtained in $5.59-5.94$ GeV and $15.31-15.67$ GeV, respectively. Compositeness of exotic states, such as the inner quark distance, magnetic moment and dominant component, are also analyzed. These exotic hadrons in triply heavy sector are expected to be confirmed in future high energy experiments.

[3] 2407.14961

Heavy four-quark mesons $bc\overline{b}\overline{c}$: Scalar particle

Parameters of the heavy four-quark scalar meson $T_{\mathrm{2bc}}=bc \overline{b}\overline{c}$ are calculated by means of the sum rule method. This structure is considered as a diquark-antidiquark state built of scalar diquark and antidiquark components. The mass and current coupling of $T_{ \mathrm{2bc}}$ are evaluated in the context of the two-point sum rule approach. The full width of this tetraquark is estimated by taking into account two types of its possible strong decay channels. First class includes dissociation of $T_{\mathrm{2bc}}$ to mesons $\eta_c\eta_{b}$, $ B_{c}^{+}B_{c}^{-}$, $B_{c}^{\ast +}B_{c}^{\ast -}$ and $ B_{c}^{+}(1^3P_{0})B_{c}^{\ast-}$. Another type of processes are generated by annihilations $\overline{b}b \to \overline{q}q$ of constituent $b$-quarks which produces the final-state charmed meson pairs $D^{+}D^{-}$, $D^{0} \overline{D}^{0}$, $D^{*+}D^{*-}$, and $D^{*0}\overline{D}^{*0}$. Partial width all of these decays are found using the three-point sum rule method which is required to calculate strong couplings at corresponding meson-meson-tetraquark vertices. Predictions obtained for the mass $m=(12697 \pm 90)~\mathrm{MeV}$ and width $\Gamma[T_{\mathrm{2bc}}]=(142.4 \pm 16.9)~ \mathrm{MeV}$ of the state $T_{\mathrm{2bc}}$ are compared with alternative results, and are useful for further experimental investigations of fully heavy resonances.

[4] 2407.15606

Power counting of the pion-dilaton effective field theory

Confining QCD-like theories close to the conformal window have a ``walking'' coupling. This is believed to lead to a light singlet scalar meson in the low-energy spectrum, a dilaton, which is the pseudo Nambu--Goldstone boson for the approximate scale symmetry. Extending chiral perturbation theory to include the dilaton requires a new small parameter to control the dilaton mass and its interactions. In our previous work we derived a systematic power counting for the dilaton couplings by matching the effective low-energy theory to the underlying theory using mild assumptions. In this paper we examine two alternative power countings which were proposed in the literature based on a phenomenological picture for the conformal transition. We find that one of these power countings fails, in fact, to generate a systematic expansion; the other coincides with the power counting we derived. We also point out that the so-called $\Delta$-potential coincides with the tree-level potential of the former, invalid, power counting.

[5] 2407.15629

Concurrent VQE for Simulating Excited States of the Schwinger Model

This work explores the application of the concurrent variational quantum eigensolver (cVQE) for computing excited states of the Schwinger model. By designing suitable ansatz circuits utilizing universal SO(4) or SO(8) qubit gates, we demonstrate how to efficiently obtain the lowest two, four, and eight eigenstates with one, two, and three ancillary qubits for both vanishing and non-vanishing background electric field cases. Simulating the resulting quantum circuits classically with tensor network techniques, we demonstrate the capability of our approach to compute the two lowest eigenstates of systems with up to $\mathcal{O}(100)$ qubits. Given that our method allows for measuring the low-lying spectrum precisely, we also present a novel technique for estimating the additive mass renormalization of the lattice based on the energy gap. As a proof-of-principle calculation, we prepare the ground and first-excited states with one ancillary and four physical qubits on quantum hardware, demonstrating the practicality of using the cVQE to simulate excited states.