arXiv subjects

Nilay Bostan

Publications and source records attributed to Nilay Bostan.

At least 19 recordsLinked to original sources

arXiv2026

Induced Multi-phase Inflation with Reheating: Leptogenesis and Dark Matter Production in Metric versus Palatini

We study non-minimally coupled scalar-induced multi-phase inflation in metric and Palatini gravity, considering linear, Brans-Dicke-like, and Higgs-like sectors. The scalar spectral index lies in the range $ n_s \simeq 0.93 \ \text{--} \ 0.98 $, consistent with \textit{Planck} and combined \textit{Planck}+ACT data. The tensor-to-scalar ratio can reach $ r \sim 0.03 $ in metric, whereas Palatini models generically predict $ r \lesssim 10^{-5} $. In the Palatini case, field excursions remain sub-Planckian, and the perturbative unitarity cutoff is raised. Reheating proceeds via perturbative inflaton decays into Higgs bosons and fermionic dark matter (DM) through the portal coupling $ \lambda_{12} $ and Yukawa coupling $ y_\chi $. Radiative stability of the inflationary plateau constrains the couplings to $ y_\chi, \lambda_{12} \sim 10^{-7} \ \text{--} \ 10^{-3} $, implying $ 4\,\mathrm{MeV} \lesssim T_{\rm rh} \lesssim 10^{15}\,\mathrm{GeV} $. Palatini realizations require smaller couplings and thus a narrower reheating window. Non-thermal DM production $\chi$ from inflaton decays is viable for DM mass $ m_\chi \sim \mathrm{keV} \ \text{--} \ \mathrm{PeV} $ with $ y_\chi \lesssim 10^{-6} $ over large parameter regions. We estimate the inflaton-right-handed neutrino (RHN) Yukawa coupling $ y_N $ required for successful baryogenesis via non-thermal leptogenesis within a Type-I seesaw framework, for the lightest RHN mass $ M_{N_1} \sim 10^{9} \ \text{--} \ 10^{14}\,\mathrm{GeV} $, provided $ M_{N_1} > T_{\rm max} $, where $ T_{\rm max} $ follows from radiatively consistent reheating. In Palatini scenarios, the lower maximal temperature and tighter stability bounds further restrict the leptogenesis parameter space.

hep-ph↗

arXiv2026

Building an AI-native Research Ecosystem for Experimental Particle Physics: A Community Vision

Experimental particle physics seeks to understand the universe by probing its fundamental particles and forces and exploring how they govern the large-scale processes that shape cosmic evolution. This whitepaper presents a vision for how Artificial Intelligence (AI) can accelerate discovery in this field. We outline grand challenges that must be addressed to enable transformative breakthroughs and describe how current and planned experimental facilities can implement this vision to advance our understanding of the vast and complex physical world from the smallest to the largest scales. We show how facilities currently under construction, such as the HL-LHC, DUNE and soon EIC, can both benefit from and serve as proving grounds for this vision, while also enabling a longer-term goal for how future experiments -- like FCC-ee at CERN, IceCube-Gen2, a Muon Collider in the U.S., and smaller to mid-scale projects -- can be fully AI-native. We describe how a truly national-scale collaboration, jointly managed across large funding partners, and involving both DOE laboratories and universities, can make this happen.

hep-ex↗

arXiv2025

Grand Unification Higgs-$\mathcal{R}^2$ Inflation: Complementarity between Proton Decay and CMB Observables

We propose a predictive $SO(10)$ Grand Unified Theory (GUT) framework for cosmic inflation in the Palatini $\mathcal{R}^2$ formulation of gravity. In this model, a GUT Higgs field both drives inflation and induces intermediate-scale symmetry breaking, thereby linking primordial cosmology, gauge unification, and topological defect formation. A partial inflationary phase of $N_I \sim 10$--$17$ $e$-folds following monopole formation can dilute magnetic monopoles to abundances $Y_M \sim 10^{-35}$--$10^{-27}$. The model yields Cosmic Microwave Background (CMB) predictions of $0.955 \lesssim n_s \lesssim 0.974$, accommodating the tensions between Planck-BICEP ($n_s \approx 0.965$) and Planck+ACT ($n_s \approx 0.971$) via $\phi < M$ and $\phi > M$ branches repectively. The predicted tensor-to-scalar ratio $r \lesssim 8\times10^{-4}$ lies within current observational constraints and is accessible to forthcoming experiments, including the Simons Observatory and LiteBIRD. The resulting correlations between the unification scale $M_U$, the inflationary observables $(n_s, r)$, and proton-decay lifetimes highlight a complementarity between CMB measurements and proton-decay searches, with regions of parameter space testable in forthcoming experiments such as Hyper-Kamiokande and DUNE.

astro-ph.CO↗

arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

hep-ph↗

arXiv2025

Large Field Polynomial Inflation in Palatini $f(R,ϕ)$ Gravity

In this paper, we employ the Palatini formalism to investigate the dynamics of large-field inflation using a renormalizable polynomial inflaton potential in the context of $f(R,ϕ)$ gravity. Assuming instant reheating, we make a comparative analysis of large-field polynomial inflation (PI). We first consider the minimal and non-minimal coupling of inflaton in $R$ gravity, and then we continue with the minimally and non-minimally coupled inflaton in $f(R,ϕ)$ gravity. We scan the parameter space for the inflationary predictions ($n_s$ and $r$) consistent with the Planck and BICEP/Keck 2018 results as well as the sensitivity forecast of the future CMB-S4 and depict the compliant regions in the $ϕ_0-β$ plane where $ϕ_0$ and $β$ are two parameters of polynomial inflation model which control the saddle point of the potential and the flatness in the vicinity of this point respectively. We find that a substantial portion of the parameter space aligns with the observational data.

astro-ph.CO↗

arXiv2024

Minimally coupled $β$-exponential inflation with an $R^2$ term in the Palatini formulation

We focus on the inflationary predictions of $β$-exponential potential models, in which the inflaton is a representation of the field delineating the size of extra-dimension. Since it offers a well-motivated starting point for the study of physics at very high energies, we incorporate an $R^2$ term in the Palatini gravity. In addition, afterward the inflation, the inflaton oscillates about the minimum of the inflation potential, and reheats the universe. This occurs during the reheating phase, at which the inflaton decays into the standard model particles, which fill the universe. We extend our examination by considering the reheating effects on inflationary observables by employing the different scenarios of the reheat temperature. Supposing the standard thermal history after inflation, we display the inflationary predictions, $n_s, r, \mathrm{d}n_s/\mathrm{d}\ln k$ of $β$-exponential potential with minimal coupling in Palatini $R^2$ gravity. Also, different kinds of constraints from a variety of observations, such as BICEP/Keck, Planck 2018, as well as future possible detectable sensitivities that might be reached by CMB experiments: CMB-S4 and LiteBIRD are taken into account in this work. We indicate that our results are consistent with both the latest data and the future sensitivity forecasts of LiteBIRD/Planck and CMB-S4. Finally, the results in this study highlight the viability of our model even in the case of the existence of more stringent constraints expected from future achievable confidence level limits.

astro-ph.CO↗

arXiv2024

First constraints on non-minimally coupled Natural and Coleman-Weinberg inflation and massive neutrino self-interactions with Planck+BICEP/Keck

In this work, for the first time in literature, we study the predictions of non-minimally coupled Natural and Coleman-Weinberg potentials in the $n_s-r$ plane, and an extended $Λ$CDM model where we include non-standard self-interactions among massive neutrinos, mediated by a heavy scalar or vector boson. Constraints were derived using the Planck 2018 + BICEP/Keck 2018 datasets along with other data. For the inflationary potentials, we consider two different formulations in gravity that are non-minimally coupled to the scalar field of the inflaton: \textit{Metric and Palatini.} We only consider the self-interaction to be present among $τ$-neutrinos and only at moderate strengths. This is because strong interactions among $τ$-neutrinos, or any strength self-interaction among electron- and muon-neutrinos, as well as any strength flavor-universal interactions, are strongly disfavoured from particle physics experiments. In terms of cosmological data, we use the latest public CMB datasets from Planck 2018 and BICEP/Keck 2018 collaborations, along with other data from CMB lensing, BAO, RSD, and SNe Ia luminosity distance measurements. We find that there are some situations where predictions from the inflationary models are ruled out at more than 2$σ$ by the minimal $Λ$CDM$+r$ model, but they are allowed in the self-interacting neutrino scenario.

astro-ph.CO↗

arXiv2023

Inflation in Symmergent Metric-Palatini Gravity

In this paper, we study the cosmological inflation phenomenon in symmergent gravity theory. Symmergent gravity is a novel framework which merges gravity and the standard model (SM) so that the gravity emerges from the matter loops and restores the broken gauge symmetries along the way. Symmergent gravity is capable of inducing the gravitational constant $G$ and the quadratic curvature coefficient $c_O$ from the loop corrections of the matter sector in a flat space-time. In the event that all the matter fields, including the beyond the standard model (BSM) sector, are mass degenerate, the vacuum energy can be expressed in terms of $G$ and $c_O$. The parameter which measures the deviation from the mass degeneracy is dubbed $\hatα$. The parameters, $c_O$ and $\hatα$, of symmergent gravity convey the information about the fermion and boson balance in the matter (SM+BSM) sector in number and in mass, respectively. In our analysis, we have investigated the space of the symmergent parameters $c_O$ and $\hatα$ wherein they produce results that comply with the inflationary observables $n_s$, $r$, and $\mathrm{d}n_s/\mathrm{d}\ln k$. We have shown that the vacuum energy together with the quadratic curvature term arising in the symmergent gravity prescription are capable of inflating the universe provided that the quadratic curvature coefficient $c_O$ is negative (which corresponds to fermion dominance in number in the matter sector) and the deviation from the mass degeneracy in the matter sector is minute for both boson mass dominance and fermion mass dominance cases.

astro-ph.CO↗

arXiv2023

Beam Test Results of the RADiCAL -- a Radiation Hard Innovative EM Calorimeter

High performance calorimetry conducted at future hadron colliders, such as the FCC-hh, poses a significant challenge for applying current detector technologies due to unprecedented beam luminosities and radiation fields. Solutions include developing scintillators that are capable of separating events at the sub-fifty picosecond level while also maintaining performance after extreme and constant neutron and ionizing radiation exposure. The RADiCAL is an approach that incorporates radiation tolerant materials in a sampling 'shashlik' style calorimeter configuration, using quartz capillaries filled with organic liquid or polymer-based wavelength shifters embedded in layers of tungsten plates and LYSO crystals. This novel design intends to address the Priority Research Directions (PRD) for calorimetry listed in the DOE Basic Research Needs (BRN) workshop for HEP Instrumentation. Here we report preliminary results from an experimental run at the Fermilab Test Beam Facility in June 2022. These tests demonstrate that the RADiCAL concept is capable of < 50 ps timing resolution.

physics.ins-det↗

arXiv2022

Tau Neutrinos in the Next Decade: from GeV to EeV

Tau neutrinos are the least studied particle in the Standard Model. This whitepaper discusses the current and expected upcoming status of tau neutrino physics with attention to the broad experimental and theoretical landscape spanning long-baseline, beam-dump, collider, and astrophysical experiments. This whitepaper was prepared as a part of the NuTau2021 Workshop.

hep-ph↗

arXiv2022

Non-minimally coupled Natural Inflation: Palatini and Metric formalism with the recent BICEP/Keck

In this work, we show the effect of the non-minimal coupling $ξϕ^2 R$ on the inflationary parameters by considering the single-field inflation and present the inflationary predictions of the appealing potential for the particle physics viewpoint: Natural Inflation, an axion-like inflaton which has a cosine-type periodic potential and the inflaton naturally emerges as a pseudo-Nambu-Goldstone boson with a spontaneously broken global symmetry. We present the inflationary predictions for this potential, $n_s$, $r$, and $α=\mathrm{d}n_s/\mathrm{d}\ln k$. In addition, we assume standard thermal history after inflation, and using this, for considered potential, we show compatible regions for the $n_s$, $r$ within the recent BICEP/Keck results.

astro-ph.CO↗

arXiv2020

Palatini Higgs and Coleman-Weinberg inflation with non-minimal coupling

We present the impact of non-minimal coupling $ξϕ^2 R$ on the inflationary parameters by taking into account the models of single-field inflation with the inflaton that has a non-zero vacuum expectation value ($v$) after the period of inflation in Palatini gravity. We discuss the well-known symmetry breaking type potentials, namely the Higgs potential and Coleman-Weinberg potential. We show the inflationary predictions of these potentials, for both $ϕ>v$ and $ϕ<v$ inflation, the regions in the $v-ξ$ plane for which the values of $n_s$ and $r$ are in agreement with the recent measurements. We also show the linear inflation behavior as a solution of Coleman-Weinberg potential for $ξv^2=1$ limit. Finally, we take into account the inflationary predictions of Coleman-Weinberg potential for preferred $ξ$ values as a function of $v$ in Palatini formalism.

gr-qc↗

arXiv2019

Preheating in radiative corrections to $ϕ^4$ inflation with non-minimal coupling in Palatini formulation

We discuss the impact of the preheating stage in radiative corrections due to interaction of the inflaton to fermions to $ϕ^4$ inflation with non-minimal coupling in Palatini formulation. In Palatini inflation with large non-minimal coupling the field is allow to return to the plateau region during the reheating stage, so the average equation of state per oscillations is closer to $-1$ than to $1/3$. The incursion in the plateau leads, however, to a highly efficient tachyonic instability able to reheat the Universe in less than one e-fold. By taking into account prescription II discussed in the literature, in the wide range of $κ-ξ$, we figure out spectral index $n_s$ and tensor-to-scalar ratio $r$ which are compatible with the data given by the Keck Array/BICEP2 and Planck collaborations.

astro-ph.CO↗

arXiv2019

Scintillation Timing Characteristics of Common Plastics for Radiation Detection Excited With 120 GeV Protons

The timing characteristics of scintillators must be understood in order to determine which applications they are appropriate for. Polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET) are common plastics with uncommon scintillation properties. Here, we report the timing characteristics of PEN and PET, determined by exciting them with 120 GeV protons. The test beam was provided by Fermi National Accelerator Laboratory, and the scintillators were tested at the Fermilab Test Beam Facility. PEN and PET are found to have dominant decay constants of 34.91 ns and 6.78 ns, respectively.

physics.ins-det↗

arXiv2019

Quartic inflation and radiative corrections with non-minimal coupling

It is well known that the non-minimal coupling $ξϕ^2R$ between the inflaton and the Ricci scalar affects predictions of single field inflation models. In particular, the $λϕ^4$ quartic inflation potential with $ξ\gtrsim0.005$ is one of the simplest models that agree with the current data. After reviewing the inflationary predictions of this potential, we analyze the effects of the radiative corrections due to couplings of the inflaton to other scalar fields or fermions. Using two different prescriptions discussed in the literature, we calculate the range of these coupling parameter values for which the spectral index $n_s$ and the tensor-to-scalar ratio $r$ are in agreement with the data taken by the Keck Array/BICEP2 and Planck collaborations.

astro-ph.CO↗

arXiv2019

Quadratic, Higgs and hilltop potentials in the Palatini gravity

In this work, we study inflation with the non-minimally coupled quadratic, Standard Model (SM) Higgs and hilltop potentials through $ξϕ^2R$ term in the Palatini gravity. We first analyze observational parameters of Palatini quadratic potential as functions of $ξ$ for high-$N$ scenario and low-$N$ scenario. In addition to this, taking into account inflaton $ϕ$ has a non-zero vacuum expectation value $v$ afterwards inflation, we display observational parameters of well-known symmetry-breaking potentials type of Higgs potential and its generalizations which are hilltop potentials in the Palatini formalism for high-$N$ scenario and low-$N$ scenario. We calculate inflationary parameters of Palatini Higgs potential as functions of $v$ for different $ξ$ values where inflaton values both $ϕ>v$ and $ϕ<v$ during inflation as well as we show that observational parameters of Palatini Higgs potential in the induced gravity limit for high-$N$ scenario. On the other hand, we illustrate different from the Higgs potential the effect of $ξ$ on hilltop potentials which can agree with the observations for inflaton value solely $ϕ<v$ and $ξ$, $v\ll1$ for both two scenarios, which we mentioned above. For each considered potentials, we also display $n_s-r$ values fit the current data given by the Keck Array/BICEP2 and Planck collaborations.

astro-ph.CO↗

arXiv2019

Non-minimally coupled quartic inflation with Coleman-Weinberg one-loop corrections in the Palatini formulation

We discuss how the non-minimal coupling $ξϕ^2 R$ between the inflaton and the Ricci scalar affects predictions of single field inflation models in Palatini formalism. To transition radiation dominated era, the inflaton field $ϕ$ must interact to matter fields at the end of inflation. Interactions of the inflaton with other fields lead to radiative corrections to the inflationary potential. These radiative corrections can be explained at leading order by Coleman-Weinberg (CW) one-loop corrections. In this work, using two different prescriptions debated in the literature, the effect of radiative corrections to the potential owing to the coupling of the inflaton to bosons in Prescription I and couplings of the inflaton to bosons and fermions in Prescription II have been examined. We analyze the range of these coupling parameter values for which the spectral index $n_s$ and the tensor-to-scalar ratio $r$ are compatible with the data taken into account to the Keck Array/BICEP2 and Planck collaborations. Finally, we also show that for all the considered potentials the running of the spectral index $α=\mathrm{d} n_s/\mathrm{d} \ln k$ as a function of $κ$ for selected $ξ$ values.

gr-qc↗

arXiv2018

Inflationary predictions of double-well, Coleman-Weinberg, and hilltop potentials with non-minimal coupling

We discuss how the non-minimal coupling $ξϕ^2R$ between the inflaton and the Ricci scalar affects the predictions of single field inflation models where the inflaton has a non-zero vacuum expectation value (VEV) $v$ after inflation. We show that, for inflaton values both above the VEV and below the VEV during inflation, under certain conditions the inflationary predictions become approximately the same as the predictions of the Starobinsky model. We then analyze inflation with double-well and Coleman-Weinberg potentials in detail, displaying the regions in the $v$-$ξ$ plane for which the spectral index $n_s$ and the tensor-to-scalar ratio $r$ values are compatible with the current observations. $r$ is always larger than 0.002 in these regions. Finally, we consider the effect of $ξ$ on small field inflation (hilltop) potentials.

astro-ph.CO↗