arXiv subjects

Long-Qi Shao

Publications and source records attributed to Long-Qi Shao.

7 recordsLinked to original sources

arXiv2026

Analytic Boundaries of Infinite-Spin-Tower Amplitudes from Hidden Zero

We study the general form of meromorphic amplitudes that are compatible with unitarity, analyticity, crossing symmetry, polynomial boundedness and the hidden-zero and corresponding splitting conditions. These amplitudes are infinite-spin-tower (IST) amplitudes and are characterized by the distribution of poles. With infinitely many equidistant poles, the IST amplitudes reduce to Veneziano amplitudes. We construct such unitary amplitudes in a primal way (rule in) and find the bounds analytically. The allowed region we derive is smaller than, but close to, the region allowed by the positivity bounds (rule out). We argue that, with the conditions imposed, the analytic boundary we derive is the largest possible boundary in the primal construction of meromorphic amplitudes. This type of IST amplitude can also be extended to the fully crossing-symmetric case related to the Virasoro-Shapiro amplitude. We found from the IST amplitudes that graviton pole imposes unitarity constraints on UV spectrum.

hep-th↗

arXiv2025

Running EFT-hedron with null constraints at loop level

Implications of general properties of quantum field theory, such as causality, unitarity, and locality include constraints on the couplings of the effective field theory (EFT) coefficients. These constraints follow from the connections between the infrared (IR) and ultraviolet (UV) theory imposed by dispersion relations for four-particle amplitudes which formally allow us to express EFT couplings through the moments of positive-definite functions (imaginary parts of partial wave amplitudes) forming the EFT-hedron geometry. Previous studies of these positivity bounds were mainly focused on the weakly coupled EFTs, limiting the analysis to tree-level amplitudes of the IR theory. In this work, we extend the scope of positivity bounds including one-loop amplitudes, which is essential especially for the loops of massless particles. Examining a single scalar theory we found that the presence of massless loops cannot be reduced only to the running of EFT couplings because loops modify the crossing symmetry relations (null constraints). Our results demonstrate that while for small coupling constants, the one-loop bounds are in good agreement with the tree-level results, the allowed EFT parameter ranges can be significantly modified if a weak coupling assumption is not additionally imposed. We present the unitarity bounds on dimension-8 and dimension-10 EFT couplings beyond the weak coupling assumption in five and six spacetime dimensions. We discuss the difficulties of obtaining the constraints in forward limit in four dimensions related to the infrared singularities and show how to overcome these problems by constructing finite combinations of null constraints.

hep-th↗

arXiv2025

Non-local positivity bounds: islands in Terra Incognita

The requirements of unitarity and causality lead to significant constraints on the Wilson coefficients of an EFT expansion, known as positivity bounds. Their standard derivation relies on the crucial assumption of polynomial boundedness on the growth of scattering amplitudes in the complex energy plane, which is a property satisfied by local QFTs, and by weakly coupled string theory in the Regge regime. The scope of this work is to clarify the role of locality by deriving generalized positivity bounds under the assumption of exponential boundedness, typical of non-local QFTs where the Froissart-Martin bound is usually not satisfied. Using appropriately modified dispersion relations, we derive new constraints and find regions in the EFT parameter space that do not admit a local UV completion. Furthermore, we show that there exist EFTs that satisfy IR causality and at the same time can admit a non-local UV completion, provided that the energy scale of non-locality is of the same order or larger than the EFT cutoff. Finally, we provide an explicit example of an exponentially bounded amplitude that satisfies partial-wave unitarity and asymptotic causality.

hep-th↗

arXiv2024

Probing for an IR-fixed Point in QCD by Superallowed Gamow-Teller Transitions in Doubly Magic Nuclei

This brief note is to point out that the recent measurements at GSI and RIKEN of the superallowed Gamow-Teller transition in the doubly magic closed-shell nucleus $^{100}$Sn could give an indication for a possibly important {\it fundamental} quenching, thus-far unrecognized, of $g_A$, unambiguously distinct from nuclear correlation effects in the framework of nuclear effective field theory. The result, either confirmed or ruled out both experimentally and theory, can have strong impacts on nuclear physics vis-à-vis with nuclear effective field theory as well as on particle physics relevant for going beyond the Standard Model.

nucl-th↗

arXiv2024

$V_{lowk}$ Renormalization Group Flow, Vector Manifestation and Sound Velocity in Massive Compact Stars

The $V_{lowk}$-renormalization group approach on the surface of Fermi liquid for nuclear matter to which Tom Kuo made a pioneering contribution at Stony Brook is found to inject the pivotal input in the formulation of the generalized nuclear effective field theory with acronym ``G$n$EFT" applicable to superdense compact-star physics. A topology change in terms of skyrmions and half-skyrmions is shown to play the role of the ``putative" hadron-quark continuity (HQC)" conjectured in QCD. Crucially involved are hidden local symmetry (``HLS") and hidden scale symmetry (``HSS") with the vacuum sliding with density in nuclear medium, with the nuclear tensor force emerging as a Landau Fermi-liquid fixed-point quantity. A possibly novel paradigm, a ``Cheshire Catism," in nuclear correlations is suggested.

nucl-th↗

arXiv2023

Corrections to Landau Fermi-liquid fixed-point approximation in nonlinear bosonized theory: Application to $g_A^L$ in nuclei

We calculated in nonlinear bosonized theory $1/\bar{N}$ corrections to the Landau Fermi-liquid fixed-point (FLFP) axial-vector coupling constant in nuclear matter $g_A^L\approx 1$ to which the Landau parameter $F_1^ω$ predominantly contributes. We obtain the correction to $F_1^ω$ to calculate the correction $δg_A^L$ to the axial-vector coupling constant $g_A^L$ at the nuclear saturation density. It comes out to be extremely small, $δg_A^L\sim O(10^{-4})$. We discuss how the "dilaton-limit fixed-point (DLFP)" result $g_A=1$ can be preserved from finite nuclei to high densities relevant to massive neutron stars and its possible impact on $0νββ$ decay processes involved in going beyond the Standard Model.

nucl-th↗

arXiv2022

Scale symmetry and composition of compact star matter

The dense compact star matter is studied by using the skyrmion crystal approach. The chiral effective theory used includes the lightest scalar meson, the lowest-lying vector mesons as well as pions. Consistency with the vector manifestation and the dilaton limit fixed point at high density constrains the anomalous dimension of the gluon field $1.0 \lesssim |γ_{G^2}| \lesssim 2.0$ and leads to the significance of the scale symmetry breaking in the intrinsic parity-odd part of the effective theory. The speed of sound $v_s^2 \simeq 1/3$ and the polytropic index $γ\simeq 1$ -- both satisfy the conformal limits -- after the dilaton limit fixed point at high density but the matter is still in the hadronic phase. This means that neither the conformal speed of sound nor the smallness of the polytropic index can be used as a criterion of the onset of quark matter. These conclusions are significant for constructing the equation of state of nuclear matter.

nucl-th↗