arXiv subjects

Ananya Tapadar

Publications and source records attributed to Ananya Tapadar.

6 recordsLinked to original sources

arXiv2026

An EFT origin of Secluded Dark Matter

The present study aims to unveil a scenario with a non-minimal secluded dark sector (DS) in an effective field theory (EFT) framework. To explore this, we have examined a suitable extension of the type-X Two Higgs Doublet Model (2HDM) as a potential origin for the secluded DS. The DS comprises a dark matter (DM) candidate and a mediator particle `$a$' and possesses some non-minimal characteristics. It becomes non-thermally populated through diverse dim-6 four-Fermi operators, effectively generated by integrating out the heavier Higgs particles. The analysis further focuses on the consequences of the collision processes $\textit{DM}+ a \leftrightarrow a + a$ and $\textit{DM}+ \textit{DM} \leftrightarrow a + a$ occurring within the DS. We have investigated the significance of employing an EFT approach in tracking the temperature evolution of the DS. Within the present framework, the observed relic abundance of the DM can be realized through both dark freeze-out and freeze-in mechanisms. Further, we have delineated the permissible ranges of the relevant parameters, viz., the DM mass ($m_χ\gtrsim 20 \, \text{GeV}$), the portal coupling ($C_τ\lesssim 10^{-14}\, \text{GeV}^{-2}$), and the DS coupling ($λ\lesssim 10^{-6} \,\text{GeV}^{-2}$) by taking into account the perturbativity of the involved couplings while reproducing the observed DM relic and complying with the bounds from a successful Big Bang Nucleosynthesis (BBN) and $γ$-ray searches.

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arXiv2025

Simulation of tau decays, ambiguities and anomalous couplings

From the perspective of low energy tau decays and radiative corrections in decays, not much has changed since the last, Tau23 conference. Also, TAUOLA, tau decay library, and PHOTOS for radiative corrections in decays have not changed much, neither for QED nor for New Physics processes application. Progress was in the domain of flexibilities for applications and in the domain of New Physicists. There was progress with use of exclusive exponentiation (KKMC Monte Carlo) to evaluate quality of tau pair formation and decay factorization, with Collins-Soper and Mustraal frames. Ambiguities for New Physics or other processes could be thus addressed. Associated projects of KKMC f77 and KKMCee C++, are presented: (i) $π^+ π^-$ pair production at Belle II energies, interesting input for Pi_gammagamma(s), (ii) attribution of helicity like labels for taus in simulated HepMC3 format events, (iii) also tau polarimetric vectors prepared for user application of New Physics.

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arXiv2025

On $τ$ Spin Use with KKMCee

Spin of $τ$ represents an interesting phenomenology data point in both its production from $e^+ e^-$ collision and its subsequent decay. In precision applications such as Belle-II or FCC, where precision tagging is comparable or better than $0.1 \%$ Monte Carlo applications are usually necessary. \texttt{KKMCee}, the precision Monte Carlo program, is assuring such high precision in a broad energy range. But so far, spin effects were not easy to grasp. We introduce into \texttt{KKMCee}, \texttt{HepMC3} format output, new entries, $τ$ helicity-like information (with weights to evaluate approximation), and $τ$ polarimetric vectors to enable weight calculations to introduce hard interaction additional couplings. The physics details of the introduced implementations are presented, as well as examples of applications and ambiguities evaluation. The most recent updates and the useful codes of our work is provided at \href{https://th.ifj.edu.pl/kkmc-demos/}{https://th.ifj.edu.pl/kkmc-demos/index.html}.

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arXiv2025

Constraining Inflation via FIMP dark matter using the $β$-function with collider implications

The present study connects inflation and freeze-in type dark matter (DM) within the same setup. Although the observables in these two phenomena lie at vastly different energy scales, they have been properly handled using the RG running of couplings. For studying DM and inflation, the SM has been minimally extended by introducing an abelian dark gauge symmetry and a dark singlet scalar. In studying inflation, the SM Higgs doublet has been considered as the inflaton, which has a non-minimal coupling with the Ricci scalar. All inflationary observables have been computed at the horizon exit scale and constrained using the Planck data. Moreover, inflationary constraints have revealed strong correlations among model parameters, significantly reducing the allowed parameter space. In particular, in the Higgs mixing angle and BSM Higgs mass plane, only those values that ensure the Higgs quartic coupling remains above 0.18 are allowed. The additional gauge boson serves as a suitable DM candidate, produced via the freeze-in mechanism and stabilised by charge conjugation symmetry. The upper bound on the DM relic density further shrinks the parameter space allowed from inflationary constraints, becoming even narrower if we assume that the present vector DM constitutes the total DM density. Since DM interactions are feeble, it remains safe from all terrestrial experimental constraints. Additionally, the feeble dark matter coupling requires the dark Higgs-Ricci scalar non-minimal coupling to be negligible to satisfy Higgs inflation conditions. Finally, we have explored collider aspects and found that the trilinear and quartic Higgs vertices deviate from their SM values after incorporating inflation and DM constraints. Therefore, once we measure $κ_{3,4}$ at the future collider, we can establish the robustness of the Higgs inflation scenario.

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arXiv2023

Secluded Dark Sector and Muon $(g-2)$ in the Light of Fast Expanding Universe

The lack of information before Big Bang Neucleosynthesis (BBN) allow us to assume the presence of a new species $ϕ$ whose energy density redshifts as $a^{-(4+n)}$ where $n>0$ and $a$ is the scale factor. This non-standard cosmological setup facilitates a larger portal coupling $(ε)$ between the dark and the visible sectors even when the two sectors are not in thermal equilibrium. Here, we have considered $U(1)_{L_μ-L_τ}\otimes U(1)_X$ gauge extension of the Standard Model (SM) and studied different phases of the cosmological evolution of a thermally decoupled dark sector such as leak-in, freeze-in, reannihilation, and late-time annihilation in the presence of fast expansion. Due to the tree level kinetic mixing between $U(1)_X$ and $U(1)_{L_μ-L_τ}$ gauge bosons, the dark sector couples with the $μ$ and $τ$ flavored leptons of the SM. We show that in our scenario it is possible to reconcile the dark matter relic density and muon $(g-2)$ anomaly. In particular, we show that for $2\times 10^{-4} \lesssim ε\lesssim 10^{-3}$, $5.5{\rm MeV} \lesssim m_{Z^\prime} \lesssim 200{\rm MeV}$, $n=4$, and $1{\rm TeV} \lesssim m_χ\lesssim 10{\rm TeV}$ relic density constraint of dark matter, constraint from muon $(g-2)$ anomaly, and other cosmological, astrophysical constraints are satisfied.

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arXiv2022

Non-adiabatic evolution of dark sector in the presence of $U(1)_{L_μ-L_τ}$ gauge symmetry

In secluded dark sector scenario, the connection between the visible and the dark sector can be established through a portal coupling and its presence opens up the possibility of non-adiabatic evolution of the dark sector. To study the non-adiabatic evolution of the dark sector, we have considered a $U(1)_{L_μ- L_τ} \otimes U(1)_X$ extension of the standard model (SM). Here the dark sector is charged only under $U(1)_X$ gauge symmetry whereas the SM fields are singlet under this symmetry. Due to the presence of tree-level kinetic mixing between $U(1)_X$ and $U(1)_{L_μ- L_τ}$ gauge bosons, the dark sector evolves non-adiabatically and thermal equilibrium between the visible and dark sector is governed by the portal coupling. Depending on the values of the portal coupling ($ε$), dark sector gauge coupling ($g_X$), mass of the dark matter ($m_χ$) and mass of the dark vector boson ($m_{Z^\prime}$), we study the temperature evolution of the dark sector as well as the various non-equilibrium stages of the dark sector in detail. Furthermore we have also investigated the constraints on the model parameters from various laboratory and astrophysical searches. We have found that the parameter space for the non-adiabatic evolution of dark sector is significantly constrained for $m_{Z^\prime}$ $\lesssim 100 \, {\rm MeV}$ from the observations of beam dump experiments, stellar cooling etc. The relic density satisfied region of our parameter space is consistent with the bounds from direct detection, and self interaction of dark matter (SIDM) for the mass ratio $r \equiv m_{Z^\prime}/m_χ= 10^{-3}$ and these bounds will be more relaxed for larger values of $r$. However the constraints from measurement of diffuse $γ$-ray background flux and cosmic microwave background (CMB) anisotropy are strongest for $r = 10^{-1}$ and for smaller values of $r$, they are not significant.

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