In this study, we investigate a scenario based on the effects of the Loop Quantum Gravity (LQG) on the electromagnetic sector of the Standard Model of Fundamental Interactions and Particle Physics (SM). Starting from a post-Maxwellian version of electromagnetism that includes LQG effects, we derive and discuss the influence of LQG parameters on classical quantities such as the components of the stress-tensor. Furthermore, we inspect the propagation of electromagnetic waves and examine the optical properties of the QED vacuum in this scenario. Among these, we contemplate the combined effect of the LQG parameters and a homogeneous background magnetic field on the propagation of electromagnetic waves by considering issues such as group velocities and refractive indices of the QED vacuum, in detail. Finally, with the aid of the previously analyzed LQG-extended photonic dispersion relations, we re-discuss the kinematics of the Compton effect and conclude that an interesting nonlinear profile emerges in the wavelengths of the incoming and deflected photons.

Brazil

P.A.L. Mourão

G.L.L.W. Levy

J.A. Helayël-Neto

Reassessing aspects of LQG-modified dispersion relations of photons * P. A. L. Mourão is support by CAPES. G. L. L. W. L. Levy is support by the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Grant No. E-26/202.437/2024.

<p>We study the tree-level scattering of massless scalars followed by an emission of a soft graviton in the small compact region inside the static patch in de Sitter space. We derive in the small cosmological constant limit the perturbative corrections to the Weinberg soft graviton theorem. Exploiting the remarkable relationship between asymptotic symmetries and soft theorems in flat space, we derive perturbative corrections to the supertranslation Ward identity. We further show that the derived supertranslation Ward identity reduces to the perturbative soft graviton theorem for the same choice of the supertranslation parameter as in flat space.</p>

China

Pratik Chattopadhyay

India

Divyesh N. Solanki

de Sitter corrections to supertranslation Ward identity and soft graviton theorem

The states of a single photon in four-dimensional de Sitter (dS) spacetime form a Unitary Irreducible Representation (UIR) of SO(1,4), which we call the photon UIR. While in flat spacetime photons are intimately tied to gauge symmetry, we demonstrate that in de Sitter, photon states emerge generically in any quantum field theory, even without an underlying U(1) gauge field. We derive a Källén-Lehmann representation for antisymmetric tensor two-point functions and show that numerous composite operators constructed from massive free fields can create states in the photon UIR. Remarkably, we find that some of these operators exhibit two-point functions with slower late-time and large-distance decay than the electromagnetic field strength itself, challenging the conventional notion that photons dominate the infrared regime. Using our spectral representation, we establish non-perturbative bounds on the late-time behavior of electric and magnetic fields in de Sitter, with potential implications for primordial magnetogenesis. Through one-loop calculations, we demonstrate that both the creation of photon states and the enhanced late-time large-distance behavior persist in weakly interacting theories.

Switzerland

Manuel Loparco

João Penedones

Germany

Yannis Ulrich

What is a photon in de Sitter spacetime?

The perturbative corrections to soft photon theorems with massive scalars in de Sitter spacetime were computed in (Bhatkar and Jain in J High Energy Phys 2023:55, 2023). However, the massless limit of the scalar modes is ill-defined in their work. It therefore is ambiguous to take the massless limit of the soft factors. In this paper, we derive the massless scalar modes in $\textit{d}$-dimensional de Sitter spacetime and use it to compute the perturbative corrections to the leading and sub-leading soft photon theorems. Our framework corresponds to tree level scattering of massless scalars followed by an emission of a soft photon in a compact region of the static patch of de Sitter. We show that our results are consistent with (Bhatkar and Jain in J High Energy Phys 2023:55, 2023) in the massless limit and we comment on the universality of our results.

Perturbative corrections to soft photon theorems for massless scalar QED in de Sitter spacetime

We investigate torsion-driven cosmological dynamics within the framework of Einstein–Cartan gravity using the De Donder–Weyl Hamiltonian formalism, where the tetrad and Lorentz connection act as independent variables and the Hamiltonian includes quadratic Riemann Cartan corrections. Embedding this theory in an FLRW background, we derive the corresponding torsion-modified Friedmann equations and analyze their solutions across radiation and matter-dominated epochs. The commonly assumed power law form $$a(t)=\beta t^{\alpha }$$ is shown to generate multiple solution branches, many of which can be considered to be “unphysical”. A hybrid solution, $$a(t)=Ct^{\alpha }e^{Dt^{\beta }}$$ emerges in the special case $$g_1=0$$ , where the quadratic Riemann–Cartan term vanishes. For $$g_1\not =0,$$ the equations become nonlinear, precluding closed-form analytic solutions. These findings highlight the limitations of the power-law approximation and identify the restricted conditions under which torsion can coherently drive cosmic expansion.

Aarav Shah

France

Maxim Khlopov

Russia

Maxim Krasnov

Cosmology in the De Donder–Weyl formulation of Einstein–Cartan gravity

Correlators of large-scale fluctuations produced during cosmic inflation are major observables of inflationary cosmology. In cosmological collider physics, many interesting correlators are generated through loop processes. However, ultraviolet divergences often appear when computing the loop correlators, and a regularization is required. In this work, Källén-Lehmann representation and dimensional regularization are used to analytically compute various correlators with a bubble loop of massive bulk propagators in de Sitter spacetime. Examples include 4-point and 2-point correlators with 1-loop bubbe exchanges of derivatively coupled massive scalars or massive spin-1 bosons.

Hongyu Zhang

Dimensional regularization of bubble diagrams in de Sitter spacetime

<p>We show that mono-energetic axions are produced in abundance through nuclear de-excitations in nearby galaxies such as M87, which is the central galaxy of the Virgo cluster, and the starburst galaxy M82. If the axion couples to both nucleons and photons and is ultralight, then monochromatic hard x-ray signatures are induced by the subsequent axion-to-photon conversion in the magnetic fields permeating these systems. We search for evidence of such signals using NuSTAR data, focusing specifically on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Fe</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>57</mn></mrow></mmultiscripts></mrow></math> de-excitation line at 14.4 keV, and we catalog other potentially relevant nuclear lines. We find no evidence for axions from M87 or M82 and set stringent constraints on the combined axion-nucleon and axion-photon coupling at the level of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">|</mo><msub><mrow><mi>g</mi></mrow><mrow><mi>a</mi><mi>n</mi><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>g</mi></mrow><mrow><mi>a</mi><mi>γ</mi><mi>γ</mi></mrow></msub><mo stretchy="false">|</mo><mo>≲</mo><mn>1.1</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>22</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>GeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math> in the limit <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>a</mi></msub><mo>≲</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>10</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math> at 95% confidence.</p>

United States

Orion Ning

Anupam Ray

CERN

Benjamin R. Safdi

Axion lines from nuclear de-excitations in galactic stellar populations

This paper investigates the quantization of the Schwarzschild–de Sitter (SdS) black hole (BH) using the Misner–Sharp–Hernandez (MSH) mass as the internal energy in a reduced phase space framework. After introducing the canonical variables of the reduced phase space, we derive a discrete spectrum for the surface areas of the BH event horizon (EH) as well as MSH masses. We utilized the MSH mass spectrum to obtain the entropy of the BH. The entropy of the BH and cosmic EHs reveals a logarithmic correction to the Bekenstein–Hawking term. Our results support the robustness of the logarithmic form of quantum corrections in SdS thermodynamics.

Türkiye

S. Jalalzadeh

Iran

H. Moradpour

Reduced phase space quantization and quantum corrected entropy of Schwarzschild-de Sitter horizons

We analyze the thermodynamic response near extremality of black holes with angular momentum in 3 + 1-dimensional de Sitter and Anti-de Sitter spacetimes. While Kerr-AdS is characterized by a single extremal limit, for Kerr-dS there are three different extremal scenarios (Cold, Nariai and Ultracold). These exhibit different near horizon geometries, with AdS , dS and Mink factors respectively. We analyze each extremal case and contrast the response once the black holes are taken out of extremality. We study the perturbations of the near horizon geometry at the level of the 4D metric, considering a consistent truncation for the metric fluctuations, and find solutions to the linearized Einstein equations. We characterize the perturbations that are responsible for the deviations away from extremality and show that their dynamics is governed by a Schwarzian theory. We treat the Ultracold case separately, detailing how the thermodynamics in 4D is reflected in the near horizon dynamics.

Belgium

Francesca Mariani

Italy

Chiara Toldo

Gravitational dynamics of near-extreme Kerr (Anti-)de Sitter black holes

We discuss a cosmological scenario where an effective violation of the strong energy condition (SEC) is realized through a coupling between SEC-fulfilling dark matter (DM) and dark energy (DE). Although the SEC-violating solutions might in principle last for an arbitrarily long time, we highlight several challenges that string realizations must face: most notably, these are the identification of suitable heavy states and their relationship with the theory cutoff. Furthermore, we discuss a black-hole argument that still allows for long-lived epochs of cosmic acceleration, but that prevents them from lasting forever. We also discuss negative potentials in the presence of a tower of light states, showing that the DM/DE coupling can push the theory towards regions of parametric control.

Gary Shiu

Flavio Tonioni

Hung Tran

Long-lived SEC violation via DM/DE couplings