arXiv subjects

C. Pallis

Publications and source records attributed to C. Pallis.

At least 19 recordsLinked to original sources

arXiv2026

Kinetically Modified Palatini Inflation Meets ACT Data

We show that the coexistence of a non-minimal coupling to gravity $f_{\mathcal{R}}=1+c_{\mathcal{R}} ϕ^{n/2}$ with a kinetic mixing of the form $f_K = f_{\mathcal{R}}^m$ -- where $n=2$ and $4$ and $0.5 \leq m \leq 10$ -- reconciles chaotic inflation based on the $ϕ^n$ potential with the recent ACT results, if we adopt the Palatini formulation of gravity. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. The model can be also embedded in supergravity by introducing two chiral superfields and a monomial superpotential, linear with respect to the inflaton-accompanying field. Its stabilization is achieved thanks to a compact contribution to the Kaehler potential, whose the inflationary part includes an holomorphic logarithmic term and a real one multiplying a shift-symmetric quadratic polynomial term.

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arXiv2026

Induced-Gravity Palatini-Like Higgs Inflation in Supergravity Confronts ACT DR6

We formulate within Supergravity a model of induced-gravity inflation, excellently consistent with ACT DR6, inspired by the Palatini gravity. The inflaton belongs in the decomposition of a conjugate pair of Higgs superfields which lead to the spontaneous breaking of a U(1)B-L symmetry at a scale close to the range (0.102-5.85)x10^16 GeV. The inflaton field is canonically normalized thanks to a real and shift-symmetric contribution into the Kaehler potential. It also includes two separate holomorphic and antiholomorphic logarithmic terms, the argument of which can be interpreted as the coupling of the inflaton to the Ricci scalar. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. Embedding the model in a B-L extension of the MSSM we show how the mu parameter can be generated and non-thermal leptogenesis can be successfully realized. An outcome of our scheme is split SUSY with gravitino mass in the range (40-60) PeV, which is consistent with the results of LHC on the Higgs boson mass.

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arXiv2026

F-Term Hybrid Inflation, Metastable Cosmic Strings and Low Reheating in View of ACT

We consider the formation of metastable cosmic strings in a left-right unified theory. The produced monopoles are diluted by a stage of F-term hybrid inflation (FHI) which is realized consistently with the SUSY breaking and a global $U(1)$ $R$ symmetry in the context of a $U(1)_{\rm R}\times U(1)_{B-L}$ extension of MSSM. The hidden-sector Kaehler manifold enjoys an enhanced $SU(1,1)/U(1)$ symmetry with the scalar curvature determined by the achievement of a SUSY-breaking de Sitter vacuum without ugly tuning. FHI turns out to be compatible with data -- including the recent ACT results --, provided that the magnitude of the emergent soft tadpole term is confined in the range $(0.1-70)$ TeV, and it is accompanied with the production of cosmic strings. Their dimensionless tension $Gμ_{\rm cs}\simeq(1-11)\cdot10^{-8}$ interprets the present observations from PTA experiments on the stochastic background of gravitational waves. The $μ$ parameter of MSSM arises by appropriately adapting the Giudice-Masiero mechanism and facilitates the out-of-equilibrium decay of the $R$ saxion at a reheat temperature lower than about $34$ GeV. The SUSY mass scale turns out to lie in the PeV region.

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arXiv2026

From N- to (p,N)- Inflationary Attractors in view of ACT

We review two types of fractional Kaehler potentials $K$ which reduce, along the inflationary path, to the form $N/(1-ϕ^{q_{\rm M}})^{p}$ with $q_{\rm M}=1$ or $2$ and $0.1\leq p\leq10$. Their coexistence, within a non-linear sigma model, with chaotic inflationary potentials of the form $ϕ^n$ (where $n=2$ or $4$) determines, independently from $q_{\rm M}$ and $n$, a class of $(p,N)$-inflationary attractors which leads to observables compatible with the ACT DR6. An implementation of these models in the context of supergravity can be also achieved by introducing two chiral superfields and a monomial superpotential, linear with respect to the inflaton-accompanying field, and supplementing the $K$'s above with a shift symmetry. Although inflation is attained for subplanckian inflaton values, the tensor-to-scalar ratio obtained for certain $N$ values can be possibly observable in the near future.

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arXiv2026

ACT-Consistent B-L Higgs Inflation in Supergravity

We consider a renormalizable extension of the minimal supersymmetric standard model (MSSM) endowed by an R and a gauged B - L symmetry. The model incorporates chaotic inflation driven by a quartic potential, associated with the Higgs superfields which lead to a spontaneous breaking of U(1)B-L. Consistency with the ACT data is achieved by considering a fractional shift-symmetric Kaehler potential which includes two free parameters (p,N) constrained in the ranges 1.355<p<6.7 and 6x10^-5<N<0.7. An explanation of the mu term of the MSSM is also provided, under the condition that a related parameter in the superpotential is somewhat small. Baryogenesis occurs via non-thermal leptogenesis which is also realized by the inflaton's decay to the lightest and/or next-to-lightest right-handed neutrinos for normal ordered light neutrino masses.

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arXiv2026

Updating GUT-Scale Pole Higgs Inflation After ACT DR6

We consider models of chaotic inflation driven by the real parts of a conjugate pair of Higgs superfields involved in the spontaneous breaking of a grand unification symmetry at a scale assuming its value within MSSM. We combine a superpotential, which is uniquely determined by applying a continuous R symmetry, with two fractional shift-symmetric Kaehler potentials introducing two free parameters (p,N). The inflationary observables provide an excellent match to the recent ACT data for 1.355<=p<=6.7 and 6x10^-5<= N<=0.7. The attainment of inflation allows for subplanckian inflaton values and possibly detectable primordial gravitational waves with (p,N) values of order unity. A solution to the mu problem of MSSM and baryogenesis via non-thermal leptogenesis can be also accommodated by embedding the model into a B-L extension of MSSM.

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arXiv2025

Memories of Prof. George Lazarides

I present some memories of my Ph.D supervisor and, later, collaborator but always encouraging supporter Prof. G. Lazarides. Some of his contributions to our common and related scientific activities on the phenomenology of MSSM and inflation are also summarized.

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arXiv2025

ACT-Inspired Kaehler-Based Inflationary Attractors

We develop a new class of cosmological attractors which are compatible with the recent ACT results. They are based on two types of fractional Kaehler potentials, K, for a gauge-singlet inflaton phi which reduce, along the inflationary path, to the form N/(1-phi^qM)^p with qM=1, 2 and 0.1< p<10. The combination of these K's with the chaotic potentials phi^n (where n=2, 4) within a non-linear sigma model leads to inflationary observables which are consistent with the current data and largely independent from qM and n. Endowing these K's with a shift symmetry we also offer a supergravity realization of our models introducing two chiral superfields and a monomial superpotential, linear with respect to the inflaton-accompanying field. The attainment of inflation with subplanckian inflaton values and the large values for the tensor-to-scalar ratio, which increases with N, are two additional attractive features of our proposal.

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arXiv2025

High-Scale SUSY from Sgoldstino Inflation

We review a number of unimodular no-scale supergravity models with F-term SUSY breaking which support technically natural de Sitter vacua. A variant of these models develops a stage of inflection-point inflation which can be realized for subplanckian field values consistently with the observational data. For central value of the spectral index ns, the necessary tuning is of the order of 10^-6, the tensor-to-scalar ratio is tiny whereas the running of ns is around -3x10^-3. Our proposal is compatible with high-scale SUSY and the results of LHC on the Higgs boson mass.

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arXiv2025

F-Term Hybrid Inflation and SUSY Breaking

We consider F-term hybrid inflation and supersymmetry breaking in the context of a model which largely respects a global U(1) R symmetry. The Kaehler potential parameterizes the Kaehler manifold with an enhanced U(1)_Rx(SU(1,1)/U(1)) symmetry, where the scalar curvature of the second factor is determined by the achievement of a supersymmetry-breaking de Sitter vacuum without ugly tuning. The magnitude of the emergent soft tadpole term for the inflaton can be adjusted in the range (1.2-460) TeV -- increasing with the dimensionality of the representation of the waterfall fields -- so that the inflationary observables are in agreement with the observational requirements. The mass scale of the supersymmetric partners turns out to lie in the region (0.09-253) PeV which is compatible with high-scale supersymmetry and the results of LHC on the Higgs boson mass. The mu parameter can be generated by conveniently applying the Giudice-Masiero mechanism and assures the out-of-equilibrium decay of the R saxion at a low reheat temperature Trh<163 GeV.

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arXiv2025

Starobinsky Inflation with T-Model Kaehler Geometries

We present novel implementations of Starobisky-like inflation within Supergravity adopting Kaehler potentials for the inflaton which parameterize hyperbolic geometries known from the T-model inflation. The associated superpotentials are consistent with an R and a global or gauge U(1)_X symmetries. The inflaton is represented by a gauge-singlet or non-singlet superfield and is accompanied by a gauge-singlet superfield successfully stabilized thanks to its compact contribution into the total Kaehler potential. Keeping the Kaehler manifold intact, a conveniently violated shift symmetry is introduced which allows for a slight variation of the predictions of Starobinsky inflation: The (scalar) spectral index exhibits an upper bound which lies close to its central observational value whereas the constant scalar curvature of the inflaton-sector Kaehler manifold increases with the tensor-to-scalar ratio.

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arXiv2025

T-Model Higgs Inflation and Metastable Cosmic Strings

We present the formation of metastable cosmic strings (CSs) in the context of a supersymmetric (SUSY) left-right model. The SU(2)R symmetry breaking occurs during a stage of T-model (Higgs) inflation (TI) driven by an SU(2)R triplet superfield which inflates away the produced monopoles. The subsequent breaking of the remaining U(1)R x U(1)B-L symmetry, triggered due to an instability arising in the system of a pair of SU(2)R doublet superfields, leads to the production of CSs. TI is based on a quartic potential, is consistent with data thanks to the adopted hyperbolic Kaehler geometry and may be followed by successful non-thermal leptogenesis. The decay of produced CSs interprets the recent observations from PTA experiments on the stochastic background of gravitational waves with values of the superpotential coupling constants close to 10^-6-10^-8 and symmetry-breaking scales a little lower than the SUSY grand unified theory scale. A solution to the mu problem of the MSSM is also accommodated provided that mu is two to three orders of magnitude lower than the gravitino mass. The issue of the gauge coupling unification is also discussed.

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arXiv2024

PeV-Scale SUSY and Cosmic Strings from F-term Hybrid Inflation

We consider F-term hybrid inflation (FHI) and SUSY breaking in the context of a B-L extension of MSSM which largely respects a global U(1) R symmetry. The hidden sector Kaehler manifold enjoys an enhanced SU(1,1)/U(1) symmetry with the scalar curvature determined by the achievement of a SUSY-breaking de Sitter vacuum without ugly tuning. FHI turns out to be consistent with data, provided that the magnitude of the emergent soft tadpole term is confined in the range (1.2-100) TeV, and it is accompanied with the production of B-L cosmic strings. If these are metastable they interpret the present observations from PTA experiments on the stochastic background of gravitational waves with dimensionless tension Gmu~(1-9.2)x10^-8. The mu parameter of MSSM arises by appropriately adapting the Giudice-Masiero mechanism and facilitates the out-of-equilibrium decay of the R saxion at a reheat temperature lower than about 71 GeV. Due to the prolonged matter dominated era the gravitational wave signal is suppressed at high frequencies. The SUSY mass scale turns out to lie in the PeV region.

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arXiv2023

Probing the Supersymmetry-Mass Scale With F-term Hybrid Inflation

We consider F-term hybrid inflation and supersymmetry breaking in the context of a model which largely respects a global U(1) R symmetry. The Kaehler potential parameterizes the Kaehler manifold with an enhanced U(1)x(SU(1,1)/U(1)) symmetry, where the scalar curvature of the second factor is determined by the achievement of a supersymmetry-breaking de Sitter vacuum without ugly tuning. The magnitude of the emergent soft tadpole term for the inflaton can be adjusted in the range (1.2-460) TeV -- increasing with the dimensionality of the representation of the waterfall fields -- so that the inflationary observables are in agreement with the observational requirements. The mass scale of the supersymmetric partners turns out to lie in the region (0.09-253) PeV which is compatible with high-scale supersymmetry and the results of LHC on the Higgs boson mass. The mu parameter can be generated by conveniently applying the Giudice-Masiero mechanism and assures the out-of-equilibrium decay of the R saxion at a low reheat temperature Trh<~163 GeV.

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arXiv2023

Inflection-Point Sgoldstino Inflation in no-Scale Supergravity

We propose a modification of no-scale supergravity models which incorporates sgoldstino stabilization and supersymmetry (SUSY) breaking with a tunable cosmological constant by introducing a Kahler potential which yields a kinetic pole of order one. The resulting scalar potential may develop an inflection point, close to which an inflationary period can be realized for subplanckian field values consistently with the observational data. For central value of the spectral index ns, the necessary tuning is of the order of 10^-6, the tensor-to-scalar ratio is tiny whereas the running of ns is around -3x10^-3. Our proposal is compatible with high-scale SUSY and the results of LHC on the Higgs boson mass.

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arXiv2023

T-Model Higgs Inflation in Supergravity

We focus on a simple, natural and predictive T model of inflation in Supergravity employing as inflaton the Higgs field which leads to the spontaneous breaking of a U(1)_(B-L) symmetry at the SUSY GUT scale. We use a renormalizable superpotential, fixed by a U(1) R symmetry, and a Kahler potential which parameterizes the Kahler manifold SU(2,1)/(SU(2)xU(1))x(SU(2)/U(1)) with scalar curvature R_K=-6/N+2/N_0 where 0<N_0<6. The spectral index ns turns out to be close to its present central observational value and the tensor-to-scalar ratio r increases with N<36. The model can be nicely linked to MSSM offering an explanation of the magnitude of the mu parameter consistently with phenomenological data. It also allows for baryogenesis via non-thermal leptogenesis with gravitino as light as 1 TeV.

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arXiv2023

Starobinsky-Type B-L Higgs Inflation Leading Beyond MSSM

Models of induced-gravity inflation are formulated within Supergravity employing as inflaton the Higgs field which leads to a spontaneous breaking of a U(1)_{B-L} symmetry at Mgut=2x10^16 GeV. We use a renormalizable superpotential, fixed by a U(1) R symmetry, and logarithmic or semi-logarithmic Kahler potentials with integer prefactors which exhibit a quadratic non-minimal coupling to gravity. We find inflationary solutions of Starobinsky type in accordance with the observations. The inflaton mass is predicted to be of the order of 10^13 GeV. The model can be nicely linked to MSSM offering an explanation of the magnitude of the mu parameter consistently with phenomenological data. Also it allows for baryogenesis via non-thermal leptogenesis, provided that the gravitino is heavier than about 10 TeV.

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arXiv2023

From Minkowski to de Sitter Vacua with Various Geometries

New no-scale supergravity models with F-term SUSY breaking are introduced, adopting Kaehler potentials parameterizing flat or curved (compact or non-compact) Kaehler manifolds. We systematically derive the form of the superpotentials leading to Minkowski vacua. Combining two types of these superpotentials we can also determine de Sitter or anti-de Sitter vacua. The construction can be easily extended to multi-modular settings of mixed geometry. The corresponding soft SUSY-breaking parameters are also derived.

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