Center for Theoretical Physics Publications

Suppression of open heavy flavors and quarkonia in heavy-ion collisions is among the most informative probes of the quark-gluon plasma. Interpreting the full wealth of data obtained from the collision events requires a precise understanding of the evolution of heavy quarks and quarkonia as they propagate through the nearly thermal and strongly coupled plasma. Systematic theoretical studies of quarkonium time evolution in the QGP in the regime where the temperature of the QGP is much smaller than the inverse of quarkonium size have only been carried out in the past few years. Such calculations require the evaluation of a gauge-invariant correlator of chromoelectric fields dressed with Wilson lines, which is similar to, but different from, the correlation used to define the well-known arXiv:hep-ph/0605199 heavy quark diffusion coefficient. The origin of this difference has been explained in arXiv:2107.03945, arXiv:2205.04477, arXiv:2306.13127. Here we show the results of the calculation of the analogous correlator in strongly coupled \(\mathcal{N}=4\) SYM using the AdS/CFT correspondence at a finite temperature arXiv:2304.03298. While it resembles the open heavy quark case, it has some crucial differences that highlight the relevance of quantum color correlations. We will also discuss the results for the quarkonium transport coefficients obtained from this correlator, thereby establishing the first analytic results at strong coupling in this context. We find that they vanish in the strong coupling limit for an \(\mathcal{N}=4\) SYM plasma with a large number of colors.

We present an estimate of the yield of hard probes expected for collisions of the isobars \(^{96}_{44}\)Ru and \(^{96}_{40}\)Zr at collision energies reachable at RHIC and the LHC\@. These yields are proportional to the number of binary nucleon-nucleon interactions, which is characteristically different due to the presence of the large neutron skin in \(^{96}_{40}\)Zr. This provides an independent opportunity to measure the difference between the neutron skin of \(^{96}_{44}\)Ru and \(^{96}_{40}\)Zr, which can provide an important constraint on the Equation of State of cold neutron-rich matter.

The two gravitational form factors of the pion, \(A^{\pi}(t)\) and \(D^{\pi}(t)\), are computed as functions of the momentum transfer squared \(t\) in the kinematic region \(0\leq -t< 2~\text{GeV}^2\) on a lattice QCD ensemble with quark masses corresponding to a close-to-physical pion mass \(m_{\pi}\approx 170~\text{MeV}\) and \(N_f=2+1\) quark flavors. The flavor decomposition of these form factors into gluon, up/down light-quark, and strange quark contributions is presented in the \(\overline{\text{MS}}\) scheme at energy scale \(\mu=2~\text{GeV}\), with renormalization factors computed non-perturbatively via the RI-MOM scheme. Using monopole and (modified) \(z\)-expansion fits to the gravitational form factors, we obtain estimates for the pion momentum fraction and \(D\)-term that are consistent with the momentum fraction sum rule and the next-to-leading order chiral perturbation theory prediction for \(D^{\pi}(0)\).

Holography on cutoff surfaces can appear to be in tension with causality. For example, as argued by Omiya and Wei [arxiv:2107.01219], double holography seemingly allows for superluminal signalling. In this paper we argue that the brane description of double holography should be treated as an effective theory and demonstrate that causality violations due to faster-than-light communication are not visible above the associated cutoff length scale. This suggests that end-of-the-world brane models are consistent with causality and that the apparent superluminal signalling is a UV effect. Moreover, we argue that short distance non-localities generically give rise to apparent faster-than-light propagation of signals in Anti-de Sitter space. Nonetheless, superluminal signalling indicates that the causal structure on holographic cutoff surfaces needs to be modified. We propose and study three different candidate regions that might replace the domain of dependence in the brane EFT of the Karch-Randall model. These regions are defined by unitarity on the brane, through bulk entanglement wedges and through the nice slice criterion, respectively. In all dimensions, these candidate regions exclude those parts of the domain of dependence which are affected by superluminal signalling. While all three definitions agree in two dimensions, they are different in higher dimensions.

Both parameters in the Higgs field's potential, its mass and quartic coupling, appear fine-tuned to near-critical values, which gives rise to the hierarchy problem and the metastability of the electroweak vacuum. Whereas such behavior appears puzzling in the context of particle physics, it is a common feature of dynamical systems, which has led to the suggestion that the parameters of the Higgs potential could be set through some dynamical process. In this article, we discuss how this notion could be extended to physics beyond the Standard Model (SM). We first review in which sense the SM Higgs parameters can be understood as near-critical and show that this notion can be extrapolated in a unique way for a generic class of SM extensions. Our main result is a prediction for the parameters of such models in terms of their corresponding Standard Model effective field theory Wilson coefficients and corresponding matching scale. For generic models, our result suggests that the scale of new (bosonic) physics lies close to the instability scale. We explore the potentially observable consequences of this connection, and illustrate aspects of our analysis with a concrete example. Lastly, we discuss implications of our results for several mechanisms of dynamical vacuum selection associated with various Beyond-Standard-Model (BSM) constructions.

This letter presents the first lattice QCD computation of the coupled channel \(\pi\Sigma\unicode{x2013}\bar{K}N\) scattering amplitudes at energies near \(1405\,{\rm MeV}\). These amplitudes contain the resonance \(\Lambda(1405)\) with strangeness \(S=-1\) and isospin, spin, and parity quantum numbers \(I(J^P)=0(1/2^-)\). However, whether there is a single resonance or two nearby resonance poles in this region is controversial theoretically and experimentally. Using single-baryon and meson-baryon operators to extract the finite-volume stationary-state energies to obtain the scattering amplitudes at slightly unphysical quark masses corresponding to \(m_\pi\approx200\) MeV and \(m_K\approx487\) MeV, this study finds the amplitudes exhibit a virtual bound state below the \(\pi\Sigma\) threshold in addition to the established resonance pole just below the \(\bar{K}N\) threshold. Several parametrizations of the two-channel \(K\)-matrix are employed to fit the lattice QCD results, all of which support the two-pole picture suggested by \(SU(3)\) chiral symmetry and unitarity.

We use the quantum spectral curve to compute the Hagedorn temperature for ABJM theory in terms of the interpolating function \(h(\lambda)\). At weak coupling we compute this temperature up to eight-loop order, showing that it matches the known tree-level and two-loop results. At strong coupling we compute the dependence numerically, showing that it is consistent with expectations from supergravity and the plane-wave limit for the four leading terms in the strong coupling expansion, up to an overall shift of the zero-point energy for type IIA string theory on AdS\(_4\times \mathbb{C}\textrm{P}^3\). We conjecture an analytic form for this shift to leading order that is consistent with our numerical results.

The dynamics of open quantum systems can be simulated by unraveling it into an ensemble of pure state trajectories undergoing non-unitary monitored evolution, which has recently been shown to undergo measurement-induced entanglement phase transition. Here, we show that, for an arbitrary decoherence channel, one can optimize the unraveling scheme to lower the threshold for entanglement phase transition, thereby enabling efficient classical simulation of the open dynamics for a broader range of decoherence rates. Taking noisy random unitary circuits as a paradigmatic example, we analytically derive the optimum unraveling basis that on average minimizes the threshold. Moreover, we present a heuristic algorithm that adaptively optimizes the unraveling basis for given noise channels, also significantly extending the simulatable regime. When applied to noisy Hamiltonian dynamics, the heuristic approach indeed extends the regime of efficient classical simulation based on matrix product states beyond conventional quantum trajectory methods. Finally, we assess the possibility of using a quasi-local unraveling, which involves multiple qubits and time steps, to efficiently simulate open systems with an arbitrarily small but finite decoherence rate.

Recent open quantum system studies showed that quarkonium time evolution inside the quark-gluon plasma is determined by transport coefficients that are defined in terms of a gauge invariant correlator of two chromoelectric field operators connected by an adjoint Wilson line. We study the Euclidean version of the correlator for quarkonium evolution and discuss the extraction of the transport coefficients from this Euclidean correlator, highlighting its difference from other problems that also require reconstructing a spectral function, such as the calculation of the heavy quark diffusion coefficient. Along the way, we explain why the transport coefficient \(\gamma_{\rm adj}\) differs from \(\gamma_{\rm fund}\) at finite temperature at \(\mathcal{O}(g^4)\), in spite of the fact that their corresponding spectral functions differ only by a temperature-independent term at the same order. We then discuss how to evaluate the Euclidean correlator via lattice QCD methods, with a focus on reducing the uncertainty caused by infrared renormalons in determining the renormalization factor nonperturbatively.

When analyzing real-world data it is common to work with event ensembles, which comprise sets of observations that collectively constrain the parameters of an underlying model of interest. Such models often have a hierarchical structure, where "local" parameters impact individual events and "global" parameters influence the entire dataset. We introduce practical approaches for optimal dataset-wide probabilistic inference in cases where the likelihood is intractable, but simulations can be realized via forward modeling. We construct neural estimators for the likelihood(-ratio) or posterior and show that explicitly accounting for the model's hierarchical structure can lead to tighter parameter constraints. We ground our discussion using case studies from the physical sciences, focusing on examples from particle physics (particle collider data) and astrophysics (strong gravitational lensing observations).

Ergodicity of quantum dynamics is often defined through statistical properties of energy eigenstates, as exemplified by Berry's conjecture in single-particle quantum chaos and the eigenstate thermalization hypothesis in many-body settings. In this work, we investigate whether quantum systems can exhibit a stronger form of ergodicity, wherein any time-evolved state uniformly visits the entire Hilbert space over time. We call such a phenomenon complete Hilbert-space ergodicity (CHSE), which is more akin to the intuitive notion of ergodicity as an inherently dynamical concept. CHSE cannot hold for time-independent or even time-periodic Hamiltonian dynamics, owing to the existence of (quasi)energy eigenstates which precludes exploration of the full Hilbert space. However, we find that there exists a family of aperiodic, yet deterministic drives with minimal symbolic complexity -- generated by the Fibonacci word and its generalizations -- for which CHSE can be proven to occur. Our results provide a basis for understanding thermalization in general time-dependent quantum systems.

Using the supergravity dual and the plane-wave limit as a guide, we conjecture the asymptotic large coupling form of the Hagedorn temperature for planar \(\mathcal{N}=4\) super Yang-Mills to order \(1/\sqrt{\lambda}\). This is two orders beyond the presently known behavior. Using the quantum spectral curve procedure of Harmark and Wilhelm, we show that our conjectured form is in excellent agreement with the numerical results.

Hyperbolic geometry on the one-bordered torus is numerically uniformized using Liouville theory. This geometry is relevant for the hyperbolic string tadpole vertex describing the one-loop quantum corrections of closed string field theory. We argue that the Lamé equation, upon fixing its accessory parameter via Polyakov conjecture, provides the input for the characterization. The explicit expressions for the Weil-Petersson metric as well as the local coordinates and the associated vertex region for the tadpole vertex are given in terms of classical torus conformal blocks. The relevance of this vertex for vacuum shift computations in string theory is highlighted.

We identify new universal properties of the energy eigenstates of chaotic systems with local interactions, which distinguish them both from integrable systems and from non-local chaotic systems. We study the relation between the energy eigenstates of the full system and products of energy eigenstates of two extensive subsystems, using a family of spin chains in (1+1) dimensions as an illustration. The magnitudes of the coefficients relating the two bases have a simple universal form as a function of \(\omega\), the energy difference between the full system eigenstate and the product of eigenstates. This form explains the exponential decay with time of the probability for a product of eigenstates to return to itself during thermalization. We also find certain new statistical properties of the coefficients. While it is generally expected that the coefficients are uncorrelated random variables, we point out that correlations implied by unitarity are important for understanding the transition probability between two products of eigenstates, and the evolution of operator expectation values during thermalization. Moreover, we find that there are additional correlations resulting from locality, which lead to a slower growth of the second Renyi entropy than the one predicted by an uncorrelated random variable approximation.

The heavy jet mass event shape has large perturbative logarithms near the leading order kinematic threshold at \(\rho = \frac{1}{3}\). Catani and Webber named these logarithms Sudakov shoulders and resummed them at double-logarithmic level. A resummation to next-to-leading logarithmic level was achieved recently. Here, we extend the resummation using an effective field theory framework to next-to-next-to-leading logarithmic order and show how to combine it with the resummation of dijet logarithms. We also solve the open problem of an unphysical singularity in the resummed momentum space distribution, in a way similar to how it is resolved in the Drell-Yan \(q_T\) spectrum: through a careful analysis of the kinematics and scale-setting in position space. The heavy jet mass Sudakov shoulder is the first observable that does not involve transverse momentum for which position space resummation is critical. These advances may lead to a more precise extraction of the strong coupling constant from \(e^+ e^-\) data.

We propose extensions of the anti-\(k_t\) and Cambridge/Aachen hierarchical jet clustering algorithms that are designed to retain the exact jet kinematics of these algorithms, while providing an infrared-and-collinear-safe definition of jet flavour at any fixed order in perturbation theory. Central to our approach is a new technique called Interleaved Flavour Neutralisation (IFN), whereby the treatment of flavour is integrated with, but distinct from, the kinematic clustering. IFN allows flavour information to be meaningfully accessed at each stage of the clustering sequence, which enables a consistent assignment of flavour both to individual jets and to their substructure. We validate the IFN approach using a dedicated framework for fixed-order tests of infrared and collinear safety, which also reveals unanticipated issues in earlier approaches to flavoured jet clustering. We briefly explore the phenomenological impact of IFN with anti-\(k_t\) jets for benchmark tasks at the Large Hadron Collider.

We propose and analyze an approach to realize quantum computation and simulation using fermionic particles under quantum gas microscopes. Our work is inspired by a recent experimental demonstration of large-scale quantum registers, where tightly localized fermion pairs are used to encode qubits exhibiting long coherence time and robustness against laser intensity noise. We describe how to engineer the SWAP gate and high-fidelity controlled-phase gates by adjusting the fermion hopping as well as Feshbach interaction strengths. Combined with previously demonstrated single-qubit rotations, these gates establish the computational universality of the system. Furthermore, we show that 2D quantum Ising Hamiltonians with tunable transverse and longitudinal fields can be efficient simulated by modulating Feshbach interaction strengths. We present a sample-efficient protocol to characterize engineered gates and Hamiltonian dynamics based on an improved classical shadow process tomography that requires minimal experimental controls. Our work opens up new opportunities to harness existing ultracold quantum gases for quantum information sciences.

Infinite-component Chern-Simons-Maxwell theories with a periodic \(K\) matrix provide abundant examples of gapped and gapless, foliated and non-foliated fracton orders. In this paper, we study the ground state degeneracy of these theories. We show that the ground state degeneracy exhibit various patterns as a function of the linear system size -- the size of the \(K\) matrix. It can grow exponentially or polynomially, cycle over finitely many values, or fluctuate erratically inside an exponential envelope. We relate these different patterns of the ground state degeneracy with the roots of the ``determinant polynomial'', a Laurent polynomial, associated to the periodic \(K\) matrix. These roots also determine whether the theory is gapped or gapless. Based on the ground state degeneracy, we formulate a necessary condition for a gapped theory to be a foliated fracton order.

The energy-energy correlator (EEC) is an observable of wide interest for collider physics and Standard Model measurements, due to both its simple theoretical description in terms of the energy-momentum tensor and its novel features for experimental studies. Significant progress has been made in both applications and higher-order perturbative predictions for the EEC. Here, we analyze the nature of the asymptotic perturbative series for the EEC by determining its analytic form in Borel space under the bubble-sum approximation. This result provides information on the leading and subleading nonperturbative power corrections through renormalon poles. We improve the perturbative convergence of the \(\overline{\mathrm{MS}}\) series for the EEC, by removing its leading renormalon using an MSR scheme, which is independent of the bubble-sum approximation. Using the leading MSR scheme power correction determined by fits to thrust, we find good agreement with EEC OPAL data already at \({\mathcal O}(\alpha_s^2)\).

We present a description of saturation in small x deep inelastic scattering from power counting in a top-down effective theory derived from QCD. A factorization formula isolates the universal physics of the nucleus at leading power in x. The onset of saturation is then understood as a breakdown in the expansion in an emergent power counting parameter, which is defined by the matrix element of a gauge invariant operator. We demonstrate the presence of a novel collinear-soft radiation mode, which clarifies the role played by the medium size in deciding linear/non-linear evolution of the cross section in \(\ln x\).