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

Realising $\textit{F}$ -term slow-roll inflation in supergravity is non-trivial due to the well-known $\textit{η}$-problem. The common strategy to solve the problem is to impose a shift symmetry on the Kähler potential, but this often leads to a negative potential in the large-field regime. To avoid negative potentials, an additional superfield called the stabiliser is usually added with a desired interaction. An alternative mechanism in supergravity, avoiding the use of a stabiliser superfield, was earlier proposed by two of us in the setup with a single chiral superfield having inflaton and goldstino amongst its field components. In this work, we extend that alternative mechanism to multi-superfield models of inflation, thereby providing a generic framework for embedding a wide class of single- and multi-field inflation models into supergravity. We illustrate our approach by several concrete examples of multi-field inflation and clarify the conditions required to avoid tachyonic instabilities during multi-field evolution. Our proposal significantly broadens the theoretical landscape of $\textit{F}$ -term inflation models in supergravity.

South Korea

Jinn-Ouk Gong

Takahiro Terada

$\textit{F}$-term multi-field inflation in supergravity without stabiliser superfields

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.

Thailand

Kazakhstan

Italy

Andrea Addazi

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

The modified supergravity approach is applied to describe a formation of Primordial Black Holes (PBHs) after Starobinsky inflation. Our approach naturally leads to the two-(scalar)-field attractor-type double inflation, whose first stage is driven by scalaron and whose second stage is driven by another scalar field which belongs to a supergravity multiplet. The scalar potential and the kinetic terms are derived, the vacua are studied, and the inflationary dynamics of those two scalars is investigated. We numerically compute the power spectra and we find the ultra-slow-roll regime leading to an enhancement (peak) in the scalar power spectrum. This leads to an efficient formation of PBHs. We estimate the masses of PBHs and we find their density fraction (as part of Dark Matter). We show that our modified supergravity models are in agreement with inflationary observables, while they predict the PBH masses in a range between  $$10^{16}$$  <math> <msup> <mn>10</mn> <mn>16</mn> </msup> </math>   g and  $$10^{20}$$  <math> <msup> <mn>10</mn> <mn>20</mn> </msup> </math>   g. In this sense, modified supergravity provides a natural top-down approach for explaining and unifying the origin of inflation and the PBHs Dark Matter.

Primordial black holes from modified supergravity

We propose the unified models of cosmological inflation, spontaneous SUSY breaking, and the dark energy (de Sitter vacuum) in $$N=1$$ <math><mrow><mi>N</mi><mo>=</mo><mn>1</mn></mrow></math>  supergravity with the dilaton–axion chiral superfield T in the presence of an $$N=1$$ <math><mrow><mi>N</mi><mo>=</mo><mn>1</mn></mrow></math>  vector multiplet with the alternative Fayet–Iliopoulos term. By using the Kähler potential as $$K=-\alpha \log (T+\overline{T})$$ <math><mrow><mi>K</mi><mo>=</mo><mo>-</mo><mi>α</mi><mo>log</mo><mo>(</mo><mi>T</mi><mo>+</mo><mover><mi>T</mi><mo>¯</mo></mover><mo>)</mo></mrow></math>  and the superpotential as a sum of a constant and a linear term, we find that viable inflation is possible for $$3\le \alpha \le \alpha _\mathrm{max}$$ <math><mrow><mn>3</mn><mo>≤</mo><mi>α</mi><mo>≤</mo><msub><mi>α</mi><mi>max</mi></msub></mrow></math>  where $$\alpha _\mathrm{max}\approx 7.235$$ <math><mrow><msub><mi>α</mi><mi>max</mi></msub><mo>≈</mo><mn>7.235</mn></mrow></math> . Observations of the amplitude of primordial scalar perturbations fix the SUSY breaking scale in our models as high as $$10^{13}\ \hbox {GeV}$$ <math><mrow><msup><mn>10</mn><mn>13</mn></msup><mspace width="4pt"></mspace><mtext>GeV</mtext></mrow></math> . In the case of $$\alpha &gt;3$$ <math><mrow><mi>α</mi><mo>&gt;</mo><mn>3</mn></mrow></math>  the axion gets the tree-level (non-tachyonic) mass comparable to the inflaton mass.

Auttakit Chatrabhuti

Generalized dilaton–axion models of inflation, de Sitter vacua and spontaneous SUSY breaking in supergravity

We propose a four-dimensional N = 1 supergravity-based Starobinsky-type inflationary model in terms of a single massive vector multiplet, whose action includes the Dirac-Born-Infeld-type kinetic terms and a generalized (new) Fayet-Iliopoulos-type term, without gauging the R-symmetry. The bosonic action and the scalar potential are computed. The inflaton is the superpartner of the Goldstino in our model, and supersymmetry is spontaneously broken after inflation by the D-type mechanism, whose scale is related to the value of the cosmological constant.

Hiroyuki Abe

Shuntaro Aoki

Massive vector multiplet with Dirac-Born-Infeld and new Fayet-Iliopoulos terms in supergravity

We study production of gravitino and Polonyi particles in the minimal Starobinsky-Polonyi $$\mathcal {N}=1$$ <math><mrow><mi>N</mi><mo>=</mo><mn>1</mn></mrow></math>  supergravity with inflaton belonging to a massive vector supermultiplet. Our model has only one free parameter given by the scale of spontaneous SUSY breaking triggered by Polonyi chiral superfield. The vector supermultiplet generically enters the action non-minimally, via an arbitrary real function. This function is chosen to generate the inflaton scalar potential of the Starobinsky model. Our supergravity model can be reformulated as an abelian supersymmetric gauge theory with the vector gauge superfield coupled to two (Higgs and Polonyi) chiral superfields interacting with supergravity, where the U(1) gauge symmetry is spontaneously broken. We find that Polonyi and gravitino particles are efficiently produced during inflation, and estimate their masses and the reheating temperature. After inflation, perturbative decay of inflaton also produces Polonyi particles that rapidly decay into gravitinos. As a result, a coherent picture of inflation and dark matter emerges, where the abundance of produced gravitinos after inflation fits the CMB constraints as a Super Heavy Dark Matter (SHDM) candidate. Our scenario avoids the notorous gravitino and Polonyi problems with the Big Bang Nucleosynthesis (BBN) and DM overproduction.

Brazil

France

Maxim Khlopov

Gravitino and Polonyi production in supergravity

Motivated by a class of flux compactifications of type IIA strings on rigid Calabi-Yau manifolds, preserving N = 2 local supersymmetry in four dimensions, we derive a non-perturbative potential of all scalar fields from the exact D-instanton corrected metric on the hypermultiplet moduli space. Applying this potential to moduli stabilization, we find a discrete set of exact vacua for axions. At these critical points, the stability problem is decoupled into two subspaces spanned by the axions and the other fields (dilaton and Kähler moduli), respectively. Whereas the stability of the axions is easily achieved, numerical analysis shows instabilities in the second subspace.

Sergei Alexandrov

Yuki Wakimoto

Non-perturbative scalar potential inspired by type IIA strings on rigid CY

We propose a large class of supergravity models in terms of a single chiral matter superfield, leading to (almost) arbitrary single-field inflationary scalar potentials similar to the F -term in rigid supersymmetry. Those scalar potentials are positively semi-definite (in our approximation), and can preserve supersymmetry at the end of inflation. The only scalar superpartner of inflaton is stabilized by a higher-dimensional term in the Kähler potential. We argue that couplings of the inflaton to other sectors of the particle spectrum do not affect the inflationary dynamics, and briefly discuss reheating of the universe by the inflaton decays.