Journal of High Energy Physics最新文献

Liouville conformal field theory is a prototypical example of an exactly solvable quantum field theory, in the sense that the correlation functions in an arbitrary background can be determined exactly using only the constraints of unitarity and crossing symmetry. For example, the three point correlation functions are given by the famous formula of Dorn-Otto-Zamolodchikov-Zamolodchikov (DOZZ). Unlike many other exactly solvable theories, Liouville theory has a continuously tunable parameter — essentially ℏ — which is related to the central charge of the theory. Here we investigate the nature of the perturbative expansion in powers of ℏ, which is the loop expansion around a semi-classical solution. We show that the perturbative coefficients grow factorially, as expected of a Feynman diagram expansion, and take the form of an asymptotic series. We identify the singularities in the Borel plane, and show that they are associated with complex instanton solutions of Liouville theory; they correspond precisely to the complex solutions described by Harlow, Maltz, and Witten. Both single- and multi-valued solutions of Liouville appear. We show that the perturbative loop expansions around these different saddle points mix in the way expected for a trans-series expansion. Thus Liouville theory provides a calculable example of a quantum field theory where perturbative and instanton contributions can be summed up and assembled into a finite answer.

In this paper we study the bounds that can be inferred on New Physics couplings to heavy sterile neutrinos N from the recent measurements performed by the Belle collaboration of the angular analysis of ( Bto {D}^{ast}ell {overline{nu}}_{ell } ) decays, with ℓ = e, μ. Indeed, a sterile neutrino N may lead to competing ( Bto {D}^{ast}ell overline{N} ) decays and Belle might have measured an incoherent sum of these two independent channels. After reviewing the theoretical formalism required to describe this phenomenon in full generality, we first perform a bump hunt in the ( {M}_{textrm{miss}}^2 ) Belle distribution to search for evidences of an additional massive neutrino. We found in such a way a small hint at ( {M}_{textrm{miss}}^2 ) ∼ (354 MeV)². However, the Belle angular analysis is sensitive to N masses up to ( mathcal{O} )(50 MeV), preventing us to further inspect this hint. Nevertheless, we study the potential impact of this additional channel in the allowed mass range on the measured angular distributions and extract model-independent bounds on the new-physics couplings which could mediate such an interaction. In particular, in the mass window here inspected, we obtain the most stringent bounds for vector and left-handed scalar operators to date.

In any diffeomorphism invariant theory of gravity, one can define a Noether charge arising from the invariance of the Lagrangian under diffeomorphisms. We have determined the Noether charge for scalar-tensor theories of gravity, in which case the gravity is mediated by the metric tensor as well as by a scalar degree of freedom. In particular, we demonstrate that the total Noether charge within an appropriate spatial volume can be related to the heat content of the boundary surface. For static spacetimes, in these theories, there exist an “equipartition” between properly defined bulk and surface degrees of freedom. While the dynamical evolution of spacetime in these theories of scalar-tensor gravity arises due to the departure from the equipartition regime. These results demonstrate that thermodynamical interpretations for gravitational theories transcend Einstein and Lovelock theories of gravity, holding true for theories with additional scalar degrees of freedom as well. Moreover, they hold in both the Jordan and the Einstein frames. However, it turns out that there are two dynamically equivalent representations of the scalar-tensor theory in the Jordan frame, differing by total derivatives in the action, which are thermodynamically inequivalent. This depicts the importance of having a thermodynamic description, which can be used in distinguishing various dynamically equivalent representations of gravity theories beyond Einstein.

An exact solution of one-dimensional lattice gauge theory at finite temperature and non-zero chemical potential is reviewed for the gauge groups G = Z(N), U(N), SU(N) for all values of N and the number of fermion flavors N_f. Calculated are the partition function, free energy, the Polyakov loop expectation values, baryon density, quark condensate, meson and baryon correlation functions. Detailed analysis of the exact solutions is done for N = 2, 3 with one and two fermion flavors. In the large N_f limit we uncover the Roberge-Weiss phase transition and discuss its remnants at finite N_f . In the case of N_f degenerate flavors we also calculate 1) the large N limit, 2) the large N_f limit and 3) the ’t Hooft-Veneziano limit of all models. The critical behavior of the models in these limits is studied and the phase structure is described in details. A comparison of all limits with U(3) and SU(3) QCD is also performed. In order to achieve these results we explore several representations of the partition function of one-dimensional QCD obtained and described in the text.

For matrix model and QFT, we discuss how dual gravitational geometry emerges from matrix degrees of freedom (specifically, adjoint scalars in super Yang-Mills theory) and how operator algebra that describes an arbitrary region of the bulk geometry can be constructed. We pay attention to the subtle difference between the notions of wave packets that describe low-energy excitations: QFT wave packet associated with the spatial dimensions of QFT, matrix wave packet associated with the emergent dimensions from matrix degrees of freedom, and bulk wave packet which is a combination of QFT and matrix wave packets. In QFT, there is an intriguing interplay between QFT wave packet and matrix wave packet that connects quantum entanglement and emergent geometry. We propose that the bulk wave packet is the physical object in QFT that describes the emergent geometry from entanglement. This proposal sets a unified view on two seemingly different mechanisms of holographic emergent geometry: one based on matrix eigenvalues and the other based on quantum entanglement. Further intuition comes from the similarity to a traversable wormhole discussed as the dual description of the coupled SYK model by Maldacena and Qi: the bulk can be seen as an eternal traversable wormhole connecting boundary regions.

Light particles quadratically coupled to nucleons induce macroscopic forces in matter. While a quantum effect always exists, an additional force occurs in the presence of a finite density of the light particles. We compute and classify such background-induced forces for particles of spin 0, ( frac{1}{2} ), 1 in the framework of effective field theory. We show that, at short distance, the background-induced forces exhibit a universal behavior that depends solely on the moments of the phase space distribution function of the light particles.

We compute the forces in the case of dark particles densities that may realistically occur in cosmology, assuming either (i) cosmically homogeneous or (ii) virialized phase space distributions. For homogeneous distributions — analogous to cosmic neutrinos, all the background-induced forces remain, unlike the quantum ones, exponentially unsuppressed at large distance, implying that large scale fifth force experiments are highly sensitive to dark relics. Moreover at zero mass the forces from dark bosons are generically enhanced with respect to their quantum counterpart due to Bose-Einstein distribution. Overall, we find that the resulting fifth force bounds can compete with those from quantum forces. For virialized distributions — identifiable as cold dark matter, the reach is also enhanced beyond the dark matter Compton wavelength. We obtain significant bounds on sub-keV scalar cold dark matter, that can appear in certain cosmological scenarios. A thorough adaptation of the results from the Eöt-Wash experiment may produce powerful additional bounds.

In this paper, we study the scattering amplitudes and soft theorems for the sigma models with two scalars. We show that if the particles are Goldstone bosons, then you necessarily get Adler zero with no possibility for non-trivial soft theorems. For non-Goldstone bosons, the soft behavior is generically captured by the geometric soft theorem studied by Cheung et al., and the right-hand side contains derivatives of lower-point amplitudes. Inspired by the recent work on the 2D sigma models, we study one special two-scalar sigma model, where the presence of symmetries in the target space translates into a special but non-trivial soft theorem without derivatives. We further generalize the construction to two larger classes of such models and derive certain soft theorem sum rules, again avoiding the derivatives of amplitudes. Our analysis provides an interesting hierarchy of two-scalar sigma models and soft theorems, ranging from Goldstone boson case to a generic target space, and showing that there are interesting theories in between.

Recently considerable efforts have been devoted to computing cosmological correlators and the corresponding wavefunction coefficients, as well as understanding their analytical structures. In this note, we revisit the computation of these “cosmological amplitudes” associated with any tree or loop graph for conformal scalars with time-dependent interactions in the power-law FRW universe, directly in terms of iterated time integrals. We start by decomposing any such cosmological amplitude (for loop graph, the “integrand” prior to loop integrations) as a linear combination of basic time integrals, one for each directed graph. We derive remarkably simple first-order differential equations involving such time integrals with edges “contracted” one at a time, which can be solved recursively and the solution takes the form of Euler-Mellin integrals/generalized hypergeometric functions. By combining such equations, we then derive a complete system of differential equations for all time integrals needed for a given graph. Our method works for any graph: for a tree graph with n nodes, this system can be transformed into the canonical differential equations of size 4ⁿ⁻¹ equivalent to the graphic rules derived recently , and we also derive the system of differential equations for loop integrands e.g. of all-loop two-site graphs and one-loop n-gon graphs. Finally, we show how the differential equations truncate for the de Sitter (dS) case (in a way similar to differential equations for Feynman integrals truncate for integer dimensions), which immediately yields the complete symbol for the dS amplitude with interesting structures e.g. for n-site chains and n-gon cases.

The entanglement negativity ( mathcal{E} )(A : B) is a useful measure of quantum entanglement in bipartite mixed states. In random tensor networks (RTNs), which are related to fixed-area states, it was found in ref. [1] that the dominant saddles computing the even Rényi negativity ( {mathcal{E}}^{(2k)} ) generically break the ℤ_2k replica symmetry. This calls into question previous calculations of holographic negativity using 2D CFT techniques that assumed ℤ_2k replica symmetry and proposed that the negativity was related to the entanglement wedge cross section. In this paper, we resolve this issue by showing that in general holographic states, the saddles computing ( {mathcal{E}}^{(2k)} ) indeed break the ℤ_2k replica symmetry.

Our argument involves an identity relating ( {mathcal{E}}^{(2k)} ) to the k-th Rényi entropy on subregion AB^∗ in the doubled state ( {left.|{rho}_{AB}rightrangle}_{A{A}^{ast }{BB}^{ast }} ), from which we see that the ℤ_2k replica symmetry is broken down to ℤ_k. For k < 1, which includes the case of ( mathcal{E} )(A : B) at k = 1/2, we use a modified cosmic brane proposal to derive a new holographic prescription for ( {mathcal{E}}^{(2k)} ) and show that it is given by a new saddle with multiple cosmic branes anchored to subregions A and B in the original state. Using our prescription, we reproduce known results for the PSSY model and show that our saddle dominates over previously proposed CFT calculations near k = 1. Moreover, we argue that the ℤ_2k symmetric configurations previously proposed are not gravitational saddles, unlike our proposal. Finally, we contrast holographic calculations with those arising from RTNs with non-maximally entangled links, demonstrating that the qualitative form of backreaction in such RTNs is different from that in gravity.