We show how a nonlocal gravitational interaction can circumvent the Weinberg no-go theorem on cosmological constant, which forbids the existence of any solution to the cosmological constant problem within the context of local field theories unless some fine-tuning is assumed. In particular, Infinite Derivative Gravity theories hint at a possible understanding of the cosmological constant as a nonlocal gravitational effect on very large scales. In this perspective, one can describe the observed cosmic acceleration in terms of an effective field theory without relying on the fine-tuning of parameters or additional matter fields.

Italy

Salvatore Capozziello

Netherlands

Anupam Mazumdar

Giuseppe Meluccio

The Weinberg no-go theorem for cosmological constant and nonlocal gravity

We find the entanglement entropy of a subregion of the vacuum state in scalar quantum electrodynamics, working perturbatively to the two-loop level. Doing so leads us to derive the Maxwell-Proca propagator in conical Euclidean space. The area law of entanglement entropy is recovered in both the massive and massless limits of the theory, as is expected. These results yield the renormalization group flow of entanglement entropy, and we find that loop contributions suppress entanglement entropy. We highlight these results in the light of the renormalization group flow of couplings and correlators, which are increased in scalar quantum electrodynamics, so that the potential tension between the increase in correlations between two points of spacetime and the decrease in entanglement entropy between two regions of spacetime with energy is discussed. We indeed show that the vacuum of a subregion of spacetime purifies with energy in scalar quantum electrodynamics, which is related to the concept of screening.

United Kingdom

Samuel Fedida

Sougato Bose

Alessio Serafini

Entanglement entropy in scalar quantum electrodynamics

We analyze the classically scale-invariant <math><mi>B</mi><mo>−</mo><mi>L</mi></math> model in the context of resonant leptogenesis with the recently proposed mass-gain mechanism. The <math><mi>B</mi><mo>−</mo><mi>L</mi></math> symmetry breaking in this scenario is associated with a strong first-order phase transition that gives rise to detectable gravitational waves (GWs) via bubble collisions. The same <math><mi>B</mi><mo>−</mo><mi>L</mi></math> symmetry breaking also gives Majorana mass to right-handed neutrinos inside the bubbles, and their out-of-equilibrium decays can produce the observed baryon asymmetry of the Universe via leptogenesis. We show that the current LIGO-VIRGO limit on stochastic GW background already excludes part of the <math><mi>B</mi><mo>−</mo><mi>L</mi></math> parameter space, complementary to the collider searches for heavy <math><msup><mi>Z</mi><mo>′</mo></msup></math> resonances. Moreover, future GW experiments like Einstein Telescope and Cosmic Explorer can effectively probe the parameter space of leptogenesis over a wide range of the <math><mi>B</mi><mo>−</mo><mi>L</mi></math> symmetry-breaking scales and gauge coupling values.

United States

Arnab Dasgupta

P. S. Bhupal Dev

Poland

Anish Ghoshal

Gravitational wave pathway to testable leptogenesis

Quantum entanglement provides a novel way to test short distance physics in the nonrelativistic regime. We will provide a protocol to potentially test new physics by bringing two charged massive particle interferometers adjacent to each other. Being charged, the two superpositions will be entangled via electromagnetic interactions mediated by the photons, including the Coulomb and the Casimir-Polder potential. We will bring a method of entanglement based tomography to seek time evolution of very small entanglement phases to probe new physical effects mediated by hitherto unknown macroscopic force which might be responsible for entangling the two charged superpositions modeled by the Yukawa type potential. We will be able to constrain the Yukawa couplings <math><mi>α</mi><mo>≥</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>35</mn></mrow></msup></math> for <math><mi>r</mi><mo>≥</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>m</mi></math> for new physics occurring in the electromagnetic sector, and in the gravitational potential <math><msub><mi>α</mi><mi>g</mi></msub><mo>≥</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>8</mn></mrow></msup></math> for <math><mi>r</mi><mo>≥</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>m</mi></math>. Furthermore, our protocol can also constrain the axionlike particle mass and coupling, which is complimentary to the existing experimental bounds.

Peter F. Barker

Australia

Ryan J. Marshman

Entanglement based tomography to probe new macroscopic forces

The coupling between gravity and matter provides an intriguing length scale in the infrared for theories of gravity within Einstein-Hilbert action and beyond. In particular, we will show that such an infrared length scale is determined by the number of gravitons <math><msub><mrow><mi>N</mi></mrow><mrow><mi>g</mi></mrow></msub><mo>≫</mo><mn>1</mn></math> associated to a given mass in the non-relativistic limit. After tracing out the matter degrees of freedom, the graviton vacuum is found to be in a displaced vacuum with an occupation number of gravitons <math><msub><mrow><mi>N</mi></mrow><mrow><mi>g</mi></mrow></msub><mo>≫</mo><mn>1</mn></math>. In the infrared, the length scale appears to be <math><mi>L</mi><mo>=</mo><msqrt><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi>g</mi></mrow></msub></mrow></msqrt><msub><mrow><mi>ℓ</mi></mrow><mrow><mi>p</mi></mrow></msub></math>, where L is the new infrared length scale, and <math><msub><mrow><mi>ℓ</mi></mrow><mrow><mi>p</mi></mrow></msub></math> is the Planck length. In a specific example, we have found that the infrared length scale is greater than the Schwarzschild radius for a slowly moving in-falling thin shell of matter. We will argue that the appearance of such an infrared length scale in higher curvature theories of gravity, such as in quadratic and cubic curvature theories of gravity, is also expected. Furthermore, we will show that gravity is fundamentally different from the electromagnetic interaction where the number of photons, <math><msub><mrow><mi>N</mi></mrow><mrow><mi>p</mi></mrow></msub></math>, is the fine structure constant after tracing out an electron wave function.

Marko Toroš

Infrared scaling for a graviton condensate

This paper focuses on extending our previous discussion of an Abelian U(1) gauge theory involving infinite derivatives to a non-Abelian SU(N) case. The renormalization group equation (RGEs) of the SU(N) gauge coupling is calculated and shown to reproduce the local theory <math><mi>β</mi></math>-function in the limit of the nonlocal scale <math><mrow><mi>M</mi><mo>→</mo><mi>∞</mi></mrow></math>. Interestingly, the gauge coupling stops its running beyond the scale <math><mi>M</mi></math>, approaching an asymptotically conformal theory.

Nobuchika Okada

Desmond Villalba

Nonlocal non-Abelian gauge theory: Conformal invariance and <math><mi>β</mi></math>-function

In this manuscript we will present the theoretical framework of the recently proposed infinite derivative theory of gravity with a non-symmetric connection. We will explicitly derive the field equations at the linear level and obtain new solutions with a non-trivial form of the torsion tensor in the presence of a fermionic source, and show that these solutions are both ghost and singularity-free.

South Africa

Álvaro Cruz-Dombriz

Francisco Torralba

Ghost-free higher-order theories of gravity with torsion

In this paper we will consider the most general quadratic curvature action with infinitely many covariant derivatives of massless gravity in three spacetime dimensions. The action is parity invariant and torsion-free and contains the same off-shell degrees of freedom as the Einstein-Hilbert action in general relativity. In the ultraviolet, with an appropriate choice of the propagator given by the exponential of an entire function, the point-like curvature singularity can be smoothened to a Gaussian distribution, while in the infrared the theory reduces to general relativity. We will also show how to embed new massive gravity in ghost-free infinite derivative gravity in Minkowski background as one of the infrared limits. Finally, we will provide the tree-level unitarity conditions for infinite derivative gravity in presence of a cosmological constant in deSitter and Anti-deSitter spacetimes in three dimensions by perturbing the geometries.

Georg Stettinger

New massless and massive infinite derivative gravity in three dimensions

In this paper we will study -like inflation in a non-local modification of gravity which contains quadratic in Ricci scalar and Weyl tensor terms with analytic infinite derivative form-factors in the action. It is known that the inflationary solution of the local + gravity remains a particular exact solution in this model. It was shown earlier that the power spectrum of scalar perturbations generated during inflation in the non-local setup remains the same as in the local + inflation, whereas the power spectrum of tensor perturbations gets modified due to the non-local Weyl tensor squared term. In the present paper we go beyond 2-point correlators and compute the non-Gaussian parameter related to 3-point correlations generated during inflation, which we found to be different from those in the original local inflationary model and scenarios alike based on a local gravity. We evaluate non-local corrections to the scalar bi-spectrum which give non-zero contributions to squeezed, equilateral and orthogonal configurations. We show that (1) with an arbitrary sign is achievable in this model based on the choice of form-factors and the scale of non-locality. We present the predictions for the tensor-to-scalar ratio, , and the tensor tilt, . In contrast to standard inflation in a local gravity, here the possibility 0 is not excluded. Thus, future CMB data can probe non-local behaviour of gravity at high space-time curvatures.

Portugal

Alexey Koshelev

K. Kumar

Russia

Alexei Starobinsky

Non-Gaussianities and tensor-to-scalar ratio in non-local

We study the gravitational wave phenomenology in models of solitosynthesis. In such models, a first order phase transition is precipitated by a period in which nontopological solitons with a conserved global charge (Q-balls) accumulate charge. As such, the nucleation rate of critical bubbles differs significantly from thermal phase transitions. In general we find that the peak amplitude of the gravitational wave spectrum resulting from solitosynthesis is stronger than that of a thermal phase transition, while the timescale of the onset of nonlinear plasma dynamics may be comparable to Hubble. We demonstrate this explicitly in an asymmetric dark matter model, and discuss current and future constraints in this scenario.