The minimal supergravity framework is applied to a construction of new D-type single-field models of inflation in agreement with precision measurements of the cosmic microwave background radiation by Planck Collaboration, BICEP/Keck Collaboration, Atacama Cosmology Telescope and South Pole Telescope. The inflaton potential, the power spectrum of scalar perturbations, the cosmological observables and the reconstruction procedure can be very simple when using the e-folds as the running variable.

China

Yermek Aldabergenov

Japan

Russia

Sergei Ketov

Single-field D-type inflation in the minimal supergravity in light of Planck-ACT-SPT data

We investigate the impact of curvature corrections to Starobinsky inflation in light of the latest observational results from the Atacama Cosmology Telescope (ACT). While the pure Starobinsky model remains a compelling candidate for cosmic inflation, we explore how the higher-order curvature terms <math altimg='si12.svg'><msup><mi>R</mi><mn>3</mn></msup></math>, <math altimg='si13.svg'><msup><mi>R</mi><mn>4</mn></msup></math> and <math altimg='si4.svg'><msup><mi>R</mi><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msup></math> modify the inflationary predictions. Using the scalar-tensor formulation of <math altimg='si14.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></math> gravity, we derive the effective scalar potentials and compute the resulting scalar tilt <math altimg='si5.svg'><msub><mi>n</mi><mi>s</mi></msub></math>, its running index <math altimg='si15.svg'><msub><mi>&#945;</mi><mi>s</mi></msub></math> and the tensor-to-scalar ratio <math altimg='si6.svg'><mi>r</mi></math>. We show that those curvature corrections can shift the predictions to align better with the ACT data, thus providing a possible resolution to a minor discrepancy between the standard Starobinsky model and ACT observations. Our findings suggest that the modified Starobinsky models with the higher-order curvature terms offer a viable pathway to reconciling inflationary predictions with precision cosmological measurements. At the same time, measuring or constraining primordial tensor modes can help to discriminate between these corrections.

Italy

Andrea Addazi

Sergei V. Ketov

Curvature corrections to Starobinsky inflation can explain the ACT results

We extend a recently proposed framework, dubbed inflation by supersymmetry breaking, to hybrid inflation by introducing a waterfall field that allows to decouple the supersymmetry breaking scale in the observable sector from the inflation scale, while keeping intact the inflation sector and its successful predictions: naturally small slow-roll parameters, small field initial conditions and absence of the pseudo-scalar companion of the inflaton, in terms of one free parameter which is the first order correction to the inflaton Kähler potential. During inflation, supersymmetry is spontaneously broken with the inflaton being the superpartner of the goldstino, together with a massive vector that gauges the R-symmetry. Inflation arises around the maximum of the scalar potential at the origin where R-symmetry is unbroken. Moreover, a nearby minimum with tuneable vacuum energy can be accommodated by introducing a second order correction to the Kähler potential. The inflaton sector can also play the role of the supersymmetry breaking ‘hidden’ sector when coupled to the (supersymmetric) Standard Model, predicting a superheavy superparticle spectrum near the inflation scale. Here we show that the introduction of a waterfall field provides a natural way to end inflation and allows for a scale separation between supersymmetry breaking and inflation. Moreover, the study of the global vacuum describing low energy Standard Model physics can be done in a perturbative way within a region of the parameter space of the model.

Kazakhstan

France

Thailand

Ignatios Antoniadis

Auttakit Chatrabhuti

Hiroshi Isono

Hybrid inflation from supersymmetry breaking

We study in more detail the cubic constraints for  $${\mathcal N}=1$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>1</mn> </mrow> </math>   chiral superfields proposed in the earlier work Eur. Phys. J. C 81, 523 (2021), which describe low-energy goldstino-axion dynamics in global non-linearly realized supersymmetry. We generalize the constraint (i) by gauging the abelian symmetry that shifts the axion, and (ii) to supergravity. In the former case we show that after adding the abelian gauge multiplet, the construction can be formulated as a cubic nilpotent massive vector superfield. In the latter case we find explicit solution to the constraint including contributions from the supergravity multiplet. We also propose microscopic supergravity models (with linear supersymmetry), including a toy model for the string dilaton, which give rise to the cubic constraints at low energies.

United States

Aspects of cubic nilpotent superfields

We further analyze phenomenological implications of double axion monodromy inflation proposed in Ref. (D'Amico et al. [13]), in gravitational wave physics. We show that in addition to chiral gravitational waves (GW) originating from gauge field instability, the model also predicts significant amount of non-chiral, scalar-induced gravitational waves, both peaking at around the same frequencies. We find that although chiral GW density has much larger peak, non-chiral GWs can dominate away from the peak as they decay at a slower rate. This provides an interesting GW signature to be probed by future space-based interferometers such as LISA and DECIGO.

Medeu Abishev

Aigerim Abylayeva

Daulet Berkimbayev

More on gravitational waves from double monodromy inflation

We propose a novel model of the modified (Starobinsky-like) old-minimal-type supergravity coupled to a chiral matter superfield, that can simultaneously describe multi-field inflation, primordial black hole (PBH) formation, dark matter (DM), and spontaneous supersymmetry (SUSY) breaking after inflation in a Minkowski vacuum. The PBH masses in our supergravity model of double slow-roll inflation, with a short phase of “ultra-slow-roll” between two slow-roll phases, are close to  $$10^{18}$$  <math> <msup> <mn>10</mn> <mn>18</mn> </msup> </math>   g. We find that a significant PBH fraction in the allowed mass window can be supplemented by spontaneous SUSY breaking in the vacuum with the gravitino mass close to the scalaron (inflaton) mass M of the order  $$10^{13}$$  <math> <msup> <mn>10</mn> <mn>13</mn> </msup> </math>   GeV. Our supergravity model favors the composite nature of DM as a mixture of PBH and heavy gravitinos as the lightest SUSY particles. The composite DM significantly relaxes fine-tuning needed for the whole PBH-DM. The PBH-DM fraction is derived, and the second-order gravitational wave background induced by the enhanced scalar perturbations is calculated. Those gravitational waves may be accessible by the future space-based gravitational interferometers.

Inflation, SUSY breaking, and primordial black holes in modified supergravity coupled to chiral matter

Old minimal <math><mrow><mi>R</mi><mo>+</mo><msup><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> supergravity has a <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> <math><mi>R</mi></math> symmetry which rotates the chiral curvature superfield. We gauge this <math><mi>R</mi></math> symmetry and study new interactions involving the gauge multiplet in the context of inflation and supersymmetry breaking. We construct models where supersymmetry and the <math><mrow><mi>R</mi></mrow></math> symmetry are spontaneously broken during and after Starobinsky inflation, and one-loop gauge anomalies are canceled by the Green–Schwarz mechanism which can also generate Standard Model gaugino masses. The hierarchy between the auxiliary fields, <math><mrow><mo>⟨</mo><mi>F</mi><mo>⟩</mo><mo>≳</mo><mo>⟨</mo><mi>D</mi><mo>⟩</mo></mrow></math>, leads to split mass spectrum where the chiral multiplet masses are around the inflationary scale (<math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>13</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>), while the gauge multiplet masses can be arbitrarily small.

Gauging the <math><mi>R</mi></math> symmetry of old minimal <math><mi>R</mi><mo>+</mo><msup><mi>R</mi><mn>2</mn></msup></math> supergravity

We study real fifth-order superfield constraint for  $${{\mathcal {N}}}=2$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>2</mn> </mrow> </math>   vector (and tensor) multiplet and derive most general solution describing complete supersymmetry breaking, and preserving a real scalar, two goldstini, and an abelian gauge field as low-energy degrees of freedom on which both supersymmetries are realized non-linearly. The surviving scalar is identified as an axion of a broken global abelian symmetry, while its scalar partner (saxion) is eliminated in terms of the goldstini. We provide an example of a UV model giving rise to the quintic constraint, and discuss the connection of this constraint and its solution to other known superfield constraints in  $${{\mathcal {N}}}=2$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>2</mn> </mrow> </math>   and  $${{\mathcal {N}}}=1$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>1</mn> </mrow> </math>   cases.

United Kingdom

Quintic constraints for  $${{\mathcal {N}}}=2$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>2</mn> </mrow> </math>   multiplets and complete SUSY breaking

We study reheating after the end of inflation in models where the inflaton is the superpartner of goldstino and is charged under a gauged U(1) R-symmetry. We consider two classes of models – one is small field characterized by an almost flat Kähler space, and the other large field characterized by a hyperbolic Kähler space SU(1, 1)/U(1), while in both cases the inflaton superpotential is linear due to the R-symmetry. The inflationary observables of our models fit within 2 $$\sigma $$  <math> <mi>σ</mi> </math>   CMB values. Upon coupling the inflaton sector to the (supersymmetric) Standard Model, we compute the MSSM parameters, mass spectrum, and decay modes of the inflaton, with the resulting reheating temperature around  $$10^8$$  <math> <msup> <mn>10</mn> <mn>8</mn> </msup> </math>   GeV. We also find that both models can accommodate superheavy LSP dark matter, depending on the parameter choice.

Reheating after inflation by supersymmetry breaking

We find new solutions to real cubic constraints on  $$N=1$$  <math> <mrow> <mi>N</mi> <mo>=</mo> <mn>1</mn> </mrow> </math>   chiral superfields transforming under global abelian symmetries. These solutions describe the low-energy dynamics of a goldstino interacting with an axion (both belonging to the same chiral superfield) with non-linearly realized supersymmetry. We show the relation between our model and the approach of Komargodski and Seiberg for describing goldstino-axion dynamics which uses orthogonal nilpotent superfields.