Supergravity provides the natural supersymmetric framework for early universe cosmology. A broad class of inflationary models in no-scale supergravity yields tree-level predictions for cosmic microwave background (CMB) observables that closely resemble those of the Starobinsky $\textit{R}$ + $\textit{R}$ model. Using results from global supersymmetry and supergravity, we analyze radiative corrections in models with canonical and non-canonical kinetic terms, focusing particularly on Starobinsky-like no-scale supergravity models. We derive conditions on the superpotential that keep the gravitino mass finite during inflation and ensure that loop-induced corrections to the Kähler potential remain either finite or subdominant relative to the tree-level potential. We show that in some models, most notably the original no-scale supergravity model with a Wess-Zumino superpotential, radiative corrections grow at large inflaton field values and can dominate the inflationary dynamics, rendering unreliable the model predictions for CMB data. However, we identify a class of no-scale Starobinsky-like models, including the Cecotti model, in which radiative corrections remain very small for inflaton field values ≲ 8 (in Planck units), preserving the agreement of the tree-level predictions with Planck CMB data.

United Kingdom

Switzerland

John Ellis

United States

Tony Gherghetta

Japan

Kunio Kaneta

Wenqi Ke

Keith Olive

Radiative corrections in supergravity models of inflation

The postinflationary production of supermassive particles can have profound implications for the thermal history of the Universe and may leave observable imprints in the gravitational wave (GW) background. In scenarios where the inflaton couples predominantly to heavy fields, say right-handed neutrinos (RHNs), nonperturbative mechanisms such as parametric resonance can lead to their efficient production, even when their masses exceed the inflaton mass. Once produced, the RHNs emit gravitons through bremsstrahlung as they decay into the Standard Model (SM) particles via <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi><mo stretchy="false">→</mo><mo>ℓ</mo><mo>+</mo><mi>H</mi></math>, enabled by the unavoidable minimal coupling to gravity, sourcing a stochastic GW background. We study this mechanism within the framework of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi></math>-attractor inflationary models, highlighting how the resulting GW spectrum carries indirect imprints of the heavy sector and the postinflationary dynamics. This offers an observational window into otherwise inaccessible supermassive particles and provides a powerful probe of high-scale physics beyond the SM.

Shinya Kanemura

India

Dibyendu Nanda

Gravitational waves from supermassive right-handed neutrinos produced at preheating

We analyze radiative corrections to the predictions of Starobinsky-like models of inflation arising from self-interactions of the inflaton, and from its Yukawa couplings, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>y</mi></math>, to matter fermions, and dimensionful trilinear couplings, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>κ</mi></math>, to scalar fields, which could be responsible for reheating the Universe after inflation. The inflaton self-interactions are found to be of higher order in the Hubble expansion rate during inflation, and hence unimportant for CMB observations. In contrast, Einstein-frame matter couplings to an inflaton generating Starobinsky-like inflation can have significant effects on the spectral index of scalar CMB perturbations, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math>, and on the tensor-to-scalar ratio, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>r</mi></math>. Using a renormalization-group improved analysis of the effective inflationary potential, we find that the Planck measurement of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math> constrains the inflaton coupling to light fermions in the Einstein frame; <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>y</mi><mo>&lt;</mo><mn>4.5</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></mrow></math>, corresponding to an upper limit on the reheating temperature <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>RH</mi></mrow></msub><mo>&lt;</mo><mn>2</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, whereas the ACT DR6 measurement of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math> corresponds to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3.8</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>&lt;</mo><mi>y</mi><mo>&lt;</mo><mn>5.6</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1.7</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>&lt;</mo><msub><mi>T</mi><mrow><mi>RH</mi></mrow></msub><mo>&lt;</mo><mn>2.8</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, while the upper limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>r</mi></math> provide weaker constraints. Planck data also imply a constraint on a trilinear inflaton coupling to light scalars in the Einstein frame: <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>κ</mi><mo>≤</mo><mn>4</mn><mo>×</mo><msup><mn>10</mn><mn>12</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, corresponding to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>RH</mi></mrow></msub><mo>≤</mo><mn>4.2</mn><mo>×</mo><msup><mn>10</mn><mn>13</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. We further present constraints on inflaton couplings to massive fermions and scalars, and analyze constraints on couplings in the Jordan frame.

CERN

Keith A. Olive

Effects of radiative corrections on Starobinsky inflation

We propose a mechanism of preheating stage after inflation, using a new idea of parametrically amplified super-radiance. Highly coherent state, characterized by macro-coherence of scalar field coupled to produced massless particle in pairs, is created by parametric resonance effects associated with field oscillation around its potential minimum, within a Hubble volume. The state is described effectively by the simple Dicke-type of super-radiance model, and super-radiant pulse is emitted within a Hubble time, justifying neglect of cosmic expansion. Produced particles are shown to interact to change their energy and momentum distribution to realize thermal hot big bang universe. A long standing problem of heating after inflation may thus be solved. A new dark matter candidate produced at the emergence of thermalized universe is suggested as well.

Motohiko Yoshimura

Kin-ya Oda

Parametrically amplified super-radiance towards hot big bang universe

Gravitational waves have become an irreplaceable tool for exploring the post-inflationary universe. Their cosmological and astrophysical origins have been attracting numerous attention. In this Letter, we point out a novel source of ultra-high frequency gravitational waves: the decay of particles produced during the reheating era. We highlight the decays of the inflaton and the Higgs bosons in the Standard Model and in the gauged B-L model as representative cases, showing how they yield a testable gravitational wave spectrum by future observations. We find that the peak frequency and the strain in the Higgs boson decay in the gauged B-L model, when the symmetry breaking scale is higher than the inflationary scale, can be greater than those in the inflaton decay scenario. Typically, the predicted spectrum lies beyond MHz in frequency and thus calls for non-interferometric experiments. Regardless of the shape of the spectrum, on the other hand, the total energy density of the produced gravitational waves can be reached by future Big Bang nucleosynthesis limits.

Gravitational waves from particle decays during reheating

We compute the density of a spin-<math><mfrac><mn>3</mn><mn>2</mn></mfrac></math> particle, the raritron, produced at the end of inflation due to gravitational interactions. We consider a background inflaton condensate as the source of this production, mediated by the exchange of a graviton. This production greatly exceeds the gravitational production from the emergent thermal bath during reheating. The relic abundance limit sets an absolute minimum mass for a stable raritron, though there are also model-dependent constraints imposed by unitarity. We also examine the case of gravitational production of a gravitino, taking into account the goldstino evolution during reheating. We compare these results with conventional gravitino production mechanisms.

France

Yann Mambrini

Sarunas Verner

Gravitational production of spin-<math><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></math> particles during reheating

We revisit the calculation of the electron, neutron, and proton electric dipole moments (EDMs) in the constrained minimal supersymmetric standard model (CMSSM). The relatively large mass of the Higgs boson, m  H  ≃ 125 GeV coupled with the (as yet) lack of discovery of any supersymmetric particle at the LHC, has pushed the supersymmetry breaking scale to several TeV or higher. Though one might expect this decoupling to have relaxed completely any bounds on the two CP violating phases in the CMSSM (θ  μ  and θ  A ), the impressive experimental improvements in the limits on the EDMs (particularly the electron EDM) still allow us to set constraints of order (0.01−0.1)π on θ  A  and (0.001−0.1)π on θ  μ . We also discuss the impact of future improvements in the experimental limits on supersymmetric models.

Natsumi Nagata

Maxim Pospelov

South Korea

Liliana Velasco-Sevilla

Quantifying limits on CP violating phases from EDMs in supersymmetry

We study the effects of an anomalous Z′ boson on the anomalous magnetic moment of the muon (g – 2), and especially the impact of its axial coupling. We mainly evaluate the negative contribution to (g – 2) of such couplings at one-loop and look at the anomalous couplings generated at two loops. We find areas of the parameter space, where the anomalous contribution becomes comparable and even dominant compared to the one-loop contribution. We show that in such cases, the cutoff of the theory is sufficiently low, so that new charged fermions can be found in the next round of collider experiments. We comment on the realization of such a context in string theory orientifolds.

Austria

Pascal Anastasopoulos

Greece

Elias Kiritsis

Anomalous and axial Z′ contributions to g−2

We propose a new portal coupling to dark matter by taking advantage of the nonminimally coupled portal sector to the Ricci scalar. Such a portal sector conformally induces couplings to the trace of the energy-momentum tensor of matters including highly secluded dark matter particles. The portal coupling is so feeble that dark matter is produced by freeze-in processes of scatterings and/or the decay of the mediator. We consider two concrete realizations of the portal: conformally induced Higgs portal and conformally induced mediator portal. The former case is compatible with the Higgs inflation, while the latter case can be tested by dark matter direct detection experiments.

Pyungwon Ko

Wan-Il Park

Conformal portal to dark matter

We show that a metastable dark matter candidate arises naturally from the conformal transformation between the Einstein metric, where gravitons are normalized states, and the Jordan metric dictating the coupling between gravity and matter. Despite being secluded from the Standard Model by a large scale above which the Jordan metric shows modifications to the Einstein frame metric, dark matter couples to the energy momentum tensor of the Higgs field in the primordial plasma primarily. This allows for the production of dark matter in a sufficient amount, which complies with observations. The seclusion of dark matter makes it long-lived for masses <math><mo>≲</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, with a lifetime much above the age of the Universe and the present experimental limits. Such a dark matter scenario has clear monochromatic signatures generated by the decay of the dark matter candidate into neutrino and/or <math><mi>γ</mi></math> rays.

Philippe Brax

Spain

Mathias Pierre

Metastable conformal dark matter