arXiv subjects

Peera Simakachorn

Publications and source records attributed to Peera Simakachorn.

14 recordsLinked to original sources

arXiv2026

Cosmic string gravitational wave backgrounds at LISA: II. Reconstruction of conventional signals over astrophysical foregrounds

We study the reconstruction of conventional cosmic-string signals with LISA in the presence of all major known astrophysical foregrounds expected in the LISA band. These include stellar-origin black-hole binaries (SOBHBs), galactic (WDs) and extragalactic (ExWDs) white dwarfs, extreme-mass-ratio-inspirals (EMRIs), and massive black-hole binaries (MBHBs). Using the Simulation-based Inference package GWBackFinder, we perform a joint inference on the LISA noise, foregrounds, and signal, across a range of injected string tensions $G\mu$. We find that reconstructing tensions with an error $\lesssim 10\%$ requires values as large as $G\mu \gtrsim 10^{-11}$, i.e. a factor $\sim10^5$ larger than previous estimates with no foregrounds, and $\sim 10^2$ larger compared to estimates accounting only for SOBHB and WD foregrounds. This work is the second in a series initiated in Ref. arXiv:2508.05395, which aims to quantify LISA's ability to measure representative cosmic-string models.

astro-ph.CO↗

arXiv2026

Reviving Motivated Inflationary Potentials with $K$-inflation in the light of ACT

Recent ACT data favor a higher scalar spectral index $n_s$, placing models such as $\alpha$-attractor T-models and natural Inflation in tension with current observations. We propose a K-inflation framework with a field-dependent non-canonical kinetic term $G(\phi)$ that reconciles these models with the latest Planck-ACT-LB-BK18 constraints. Our analysis includes a refined calculation of the reheating equation-of-state parameter $w_{\rm re}$, avoids standard power-law approximations, and tests consistency with the Swampland Distance and de Sitter Conjectures. We find that the additional friction from the non-minimal kinetic coupling shifts both models into the favored observational regions. For the $\alpha$-attractor T-model with $n=2$, viable solutions occur for $\beta\sim \mathcal{O}(10)$, with Swampland consistency favoring $\alpha\gtrsim \mathcal{O}(10^{-3})$. This case predicts matter-like reheating and a red-tilted gravitational-wave background that is unlikely to be detected soon. In contrast, natural Inflation with $n=4,5$ is compatible with CMB constraints for $\alpha\lesssim 7,8$ and $\beta\lesssim -1$, respectively, leading to stiff reheating and a blue-tilted gravitational-wave background potentially observable by LISA, Cosmic Explorer, Einstein Telescope, DECIGO, and BBO while satisfying BBN and $\Delta N_{\rm eff}$ bounds. Combining gravitational-wave probes with Swampland criteria may therefore help distinguish possible UV completions of inflation.

gr-qc↗

arXiv2025

Cosmic string gravitational wave backgrounds at LISA: I. Signal survey, template reconstruction, and model comparison

We present a catalog of gravitational wave background (GWB) signal templates from cosmic-string networks, based on relevant models proposed in the literature. We classify templates as conventional, based on standard cosmology and Nambu-Goto results (VOS and BOS), and beyond conventional, based on modifications of a) the loop number density (LRS, super, metastable, current-carrying strings), b) the expansion history (non-standard cosmologies, extra degrees of freedom, either thermal or secluded), or c) the loop properties (birth length, power emission). Using the SBI package $\texttt{GWBackFinder}$, we quantify the reconstruction precision of each signal by LISA, scanning over their parameter space, and performing model comparisons. For conventional signals, LISA reconstructs the tension $G\mu$ with an error $\lesssim 10\%$ for $G\mu \gtrsim 5\cdot 10^{-15}$, which decreases down to $2-3\%$ for $G\mu \gtrsim 10^{-12}$. BOS and VOS modelings become distinguishable confidently for $G\mu \gtrsim 5\cdot 10^{-13}$. For beyond-conventional signals, we identify SNR and error-threshold intervals for each parameter, and determine (for few examples) the regions where they can be distinguished from conventional signals. Analogous quality reconstruction studies of cosmic-string GWBs, superimposed over leading astrophysical foregrounds in the LISA window, will be presented in a series of upcoming papers.

astro-ph.CO↗

arXiv2025

New Source for QCD Axion Dark Matter Production: Curvature Induced

We discuss a novel mechanism for generating dark matter from a fast-rolling scalar field, relevant for both inflation and rotating axion models, and apply it specifically to the (QCD) axion. Dark matter comes from scalar field fluctuations generated by the product of the curvature perturbation and the fast-rolling background field. These fluctuations can explain the totality of dark matter in a vast axion parameter space, particularly for the QCD axion, which will be targeted by upcoming experiments. We review the constraints on this mechanism and potential gravitational-wave signatures.

hep-ph↗

arXiv2025

A universal bound on the duration of a kination era

We show that primordial adiabatic curvature fluctuations generate an instability of the scalar field sourcing a kination era. We demonstrate that the generated higher Fourier modes constitute a radiation-like component dominating over the kination background after about $11$ e-folds of cosmic expansion. Current constraints on the extra number of neutrino flavors $\Delta N_{\rm eff}$ thus imply the observational bound of approximately 10 e-folds, representing the most stringent bound to date on the stiffness of the equation of state of the pre-Big-Bang-Nucleosynthesis universe.

hep-ph↗

arXiv2024

Ultrahigh frequency primordial gravitational waves beyond the kHz: The case of cosmic strings

We investigate gravitational-wave backgrounds (GWBs) of primordial origin that would manifest only at ultra-high frequencies, from kilohertz to 100 gigahertz, and leave no signal at either LIGO, Einstein Telescope, Cosmic Explorer, LISA, or pulsar-timing arrays. We focus on GWBs produced by cosmic strings and make predictions for the GW spectra scanning over high-energy scale (beyond $10^{10}$ GeV) particle physics parameters. Signals from local string networks can easily be as large as the Big Bang nucleosynthesis/cosmic microwave background bounds, with a characteristic strain as high as $10^{-26}$ in the 10 kHz band, offering prospects to probe grand unification physics in the $10^{14}-10^{17}$ GeV energy range. In comparison, GWB from axionic strings is suppressed (with maximal characteristic strain $\sim 10^{-31}$) due to the early matter era induced by the associated heavy axions. We estimate the needed reach of hypothetical futuristic GW detectors to probe such GWB and, therefore, the corresponding high-energy physics processes. Beyond the information of the symmetry-breaking scale, the high-frequency spectrum encodes the microscopic structure of the strings through the position of the UV cutoffs associated with cusps and kinks, as well as potential information about friction forces on the string. The IR slope, on the other hand, reflects the physics responsible for the decay of the string network. We discuss possible strategies for reconstructing the scalar potential, particularly the scalar self-coupling, from the measurement of the UV cutoff of the GW spectrum.

hep-ph↗

arXiv2024

Cosmological Background Interpretation of Pulsar Timing Array Data

We discuss the interpretation of the detected signal by Pulsar Timing Array (PTA) observations as a gravitational wave background (GWB) of cosmological origin. We combine NANOGrav 15-years and EPTA-DR2new data sets and confront them against backgrounds from supermassive black hole binaries (SMBHBs), and cosmological signals from inflation, cosmic (super)strings, first-order phase transitions, Gaussian and non-Gaussian large scalar fluctuations, and audible axions. We find that scalar-induced, and to a lesser extent audible axion and cosmic superstring signals, provide a better fit than SMBHBs. These results depend, however, on modeling assumptions, so further data and analysis are needed to reach robust conclusions. Independently of the signal origin, the data strongly constrain the parameter space of cosmological signals, for example, setting an upper bound on primordial non-Gaussianity at PTA scales as $|f_{nl}| \lesssim 2.34$ at 95% CL.

astro-ph.CO↗

arXiv2023

Constraining Postinflationary Axions with Pulsar Timing Arrays

Models that produce Axion-Like-Particles (ALP) after cosmological inflation due to spontaneous $U(1)$ symmetry breaking also produce cosmic string networks. Those axionic strings lose energy through gravitational wave emission during the whole cosmological history, generating a stochastic background of gravitational waves that spans many decades in frequency. We can therefore constrain the axion decay constant and axion mass from limits on the gravitational wave spectrum and compatibility with dark matter abundance as well as dark radiation. We derive such limits from analyzing the most recent NANOGrav data from Pulsar Timing Arrays (PTA). The limits are similar to the $N_{\rm eff}$ bounds on dark radiation for ALP masses $m_a \lesssim 10^{-22}$ eV. On the other hand, for heavy ALPs with $m_a\gtrsim 0.1$ GeV and $N_{\rm DW}\neq 1$, new regions of parameter space can be probed by PTA data due to the dominant Domain-Wall contribution to the gravitational wave background.

hep-ph↗

arXiv2023

Primordial Black Hole Archaeology with Gravitational Waves from Cosmic Strings

Light primordial black holes (PBHs) with masses smaller than $10^9$ g ($10^{-24} M_\odot$) evaporate before the onset of Big-Bang nucleosynthesis, rendering their detection rather challenging. If efficiently produced, they may have dominated the universe energy density. We study how such an early matter-dominated era can be probed successfully using gravitational waves (GW) emitted by local and global cosmic strings. While previous studies showed that a matter era generates a single-step suppression of the GW spectrum, we instead find a "double-step" suppression for local-string GW whose spectral shape provides information on the duration of the matter era. The presence of the two steps in the GW spectrum originates from GW being produced through two events separated in time: loop formation and loop decay, taking place either before or after the matter era. The second step - called the "knee" - is a novel feature which is universal to any early matter-dominated era and is not only specific to PBHs. Detecting GWs from cosmic strings with LISA, ET, or BBO would set constraints on PBHs with masses between $10^6$ and $10^9$ g for local strings with tension $Gμ= 10^{-11}$, and PBHs masses between $10^4$ and $10^9$ g for global strings with symmetry-breaking scale $η= 10^{15}~\mathrm{GeV}$. Effects from the spin of PBHs are discussed.

hep-ph↗

arXiv2022

Kination cosmology from scalar fields and gravitational-wave signatures

Kination denotes an era in the cosmological history corresponding to an equation of state $ω=+1$ such that the total energy density of the universe redshifts as the sixth inverse power of the scale factor. This arises if the universe is dominated by the kinetic energy of a scalar field. It has often been motivated in the literature as an era following inflation, taking place before the radiation era. In this paper, we review instead the possibility that kination is disconnected from primordial inflation and occurs much later, inside the Standard Model radiation era. We study the implications on all main sources of primordial gravitational waves. We show how this leads to very distinctive peaked spectra in the stochastic background of long-lasting cosmological sources of gravitational waves, namely the irreducible gravitational waves from inflation, and gravitational waves from cosmic strings, both local and global, with promising observational prospects. We present model-independent signatures and detectability predictions at SKA, LIGO, LISA, ET, CE, BBO, as a function of the energy scale and duration of the kination era. We then argue that such intermediate kination era is in fact symptomatic in a large class of axion models. We analyse in details the scalar field dynamics, the working conditions and constraints in the underlying models. We present the gravitational-wave predictions as a function of particle physics parameters. We derive the general relation between the gravitational-wave signal and the axion dark matter abundance as well as the baryon asymmetry. We investigate the predictions for the special case of the QCD axion. The key message is that gravitational-waves of primordial origin represent an alternative experimental probe of axion models.

hep-ph↗

arXiv2022

Cosmology with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational wave observations by LISA to probe the universe.

astro-ph.CO↗

arXiv2021

Revealing the Primordial Irreducible Inflationary Gravitational-Wave Background with a Spinning Peccei-Quinn Axion

The primordial irreducible gravitational-wave background due to quantum vacuum tensor fluctuations produced during inflation spans a large range of frequencies with an almost scale-invariant spectrum but is too low to be detected by the next generation of gravitational-wave interferometers. We show how this signal is enhanced by a short temporary kination era in the cosmological history (less than 10 e-folds), that can arise at any energy scale between a GeV and the inflationary scale $10^{16}$ GeV. We argue that such kination era is naturally generated by a spinning axion before it gets trapped by its potential. It is usually assumed that the axion starts oscillating around its minimum from its initially frozen position. However, the early dynamics of the Peccei-Quinn field can induce a large kinetic energy in the axion field, triggering a kination era, either before or after the axion acquires its mass, leading to a characteristic peak in the primordial gravitational-wave background. This represents a smoking-gun signature of axion physics as no other scalar field dynamics is expected to trigger such a sequence of equations of state in the early universe. We derive the resulting gravitational-wave spectrum, and present the parameter space that leads to such a signal as well as the detectability prospects, in particular at LISA, Einstein Telescope, Cosmic Explorer and Big Bang Observer. We show both model-independent predictions and present as well results for two specific well-motivated UV completions for the QCD axion dark matter where this dynamics is built-in.

hep-ph↗

arXiv2020

BSM with Cosmic Strings: Heavy, up to EeV mass, Unstable Particles

Unstable heavy particles well above the TeV scale are unaccessible experimentally. So far, Big-Bang Nucleosynthesis (BBN) provides the strongest limits on their mass and lifetime, the latter being shorter than 0.1 second. We show how these constraints could be potentially tremendously improved by the next generation of Gravitational-Wave (GW) interferometers, extending to lifetimes as short as $10^{-16}$ second. The key point is that these particles may have dominated the energy density of the universe and have triggered a period of matter domination at early times, until their decay before BBN. The resulting modified cosmological history compared to the usually-assumed single radiation era would imprint observable signatures in stochastic gravitational-wave backgrounds of primordial origin. In particular, we show how the detection of the GW spectrum produced by long-lasting sources such as cosmic strings would provide a unique probe of particle physics parameters. When applied to specific particle production mechanisms in the early universe, these GW spectra could be used to derive new constraints on many UV extensions of the Standard Model. We illustrate this on a few examples, such as supersymmetric models where the mass scale of scalar moduli and gravitino can be constrained up to $10^{10}$ GeV. Further bounds can be obtained on the reheating temperature of models with only-gravitationally-interacting particles as well as on the kinetic mixing of heavy dark photons at the level of $10^{-18}$.

hep-ph↗

arXiv2020

Beyond the Standard Models with Cosmic Strings

We examine which information on the early cosmological history can be extracted from the potential measurement by third-generation gravitational-wave observatories of a stochastic gravitational wave background (SGWB) produced by cosmic strings. We consider a variety of cosmological scenarios breaking the scale-invariant properties of the spectrum, such as early long matter or kination eras, short intermediate matter and inflation periods inside a radiation era, and their specific signatures on the SGWB. This requires to go beyond the usually-assumed scaling regime, to take into account the transient effects during the change of equation of state of the universe. We compute the time evolution of the string network parameters and thus the loop-production efficiency during the transient regime, and derive the corresponding shift in the turning-point frequency. We consider the impact of particle production on the gravitational-wave emission by loops. We estimate the reach of future interferometers LISA, BBO, DECIGO, ET and CE and radio telescope SKA to probe the new physics energy scale at which the universe has experienced changes in its expansion history. We find that a given interferometer may be sensitive to very different energy scales, depending on the nature and duration of the non-standard era, and the value of the string tension. It is fascinating that by exploiting the data from different GW observatories associated with distinct frequency bands, we may be able to reconstruct the full spectrum and therefore extract the values of fundamental physics parameters.

hep-ph↗