Review Papers - HIROSHIMA Nagisa

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Search for heavy dark matter from dwarf spheroidal galaxies: leveraging cascades and subhalo models

Deheng Song,Nagisa Hiroshima,Kohta Murase

Journal of Cosmology and Astroparticle Physics   2024.1  [Reviewed]  [Invited]

DOI arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Joint Work  

The Fermi Large Area Telescope (Fermi-LAT) has been widely used to search for
Weakly Interacting Massive Particle (WIMP) dark matter signals due to its
unparalleled sensitivity in the GeV energy band. The leading constraints for
WIMP by Fermi-LAT are obtained from the analyses of dwarf spheroidal galaxies
within the Local Group, which are compelling targets for dark matter searches
due to their relatively low astrophysical backgrounds and high dark matter
content. In the meantime, the search for heavy dark matter with masses above
TeV remains a compelling and relatively unexplored frontier. In this study, we
utilize 14-year Fermi-LAT data to search for dark matter annihilation and decay
signals in 8 classical dwarf spheroidal galaxies within the Local Group. We
consider secondary emission caused by electromagnetic cascades of prompt gamma
rays and electrons/positrons from dark matter, which enables us to extend the
search with Fermi-LAT to heavier dark matter cases. We also update the dark
matter subhalo model with informative priors respecting the fact that they
reside in subhalos of our Milky Way halo aiming to enhance the robustness of
our results. We place constraints on dark matter annihilation cross section and
decay lifetime for dark matter masses ranging from $10^3$ GeV to $10^{11}$ GeV,
where our limits are more stringent than those obtained by many other
high-energy gamma-ray instruments.

Other Link： http://arxiv.org/pdf/2401.15606v1

Dark Matter Search with Cherenkov Telescope Array

Nagisa Hiroshima

34th conference in the Rencontres de Blois series   2023.10

DOI arXiv

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Language：English   Publishing type：Research paper, summary (international conference)   Single Work  

Many models of dark matter (DM) are now widely considered and probed
intensively with accelerators, underground detectors, and astrophysical
experiments. Among the various approaches, high-energy astrophysical
observations are extremely useful to complement laboratory searches for some DM
candidates. In the near future, the Cherenkov Telescope Array (CTA) should
enable us to access much heavier weakly interacting massive particles, as well
as a broad range of other DM candidates. In this talk, we describe DM searches
with CTA.

Other Link： http://arxiv.org/pdf/2310.01847v1

Constraining the primordial curvature perturbation using dark matter substructure

Shin’ichiro Ando,Nagisa Hiroshima,Koji Ishiwata

Physical Review D   106 ( 10 )   2022.11  [Reviewed]  [Invited]

DOI arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：American Physical Society (APS)   Joint Work  

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.106.103014/fulltext

Semi-analytical frameworks for subhaloes from the smallest to the largest scale

Nagisa Hiroshima,Shin’ichiro Ando,Tomoaki Ishiyama

Monthly Notices of the Royal Astronomical Society   517 ( 2 )   2728 - 2737   2022.10  [Reviewed]  [Invited]

DOI arXiv

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：Oxford University Press (OUP)   Joint Work  

ABSTRACT
Substructures of dark matter halo, called subhaloes, provide important clues to understand the nature of dark matter. We construct a useful model to describe the properties of subhalo mass functions based on the well-known analytical prescriptions, the extended Press–Schechter theory. The unevolved subhalo mass functions at arbitrary mass scales become describable without introducing free parameters. The different host halo evolution histories are directly recast to their subhalo mass functions. As applications, we quantify the effects from (i) the Poisson fluctuation, (ii) the host-mass scatter, and the (iii) different tidal evolution models on observables in the current Universe with this scheme. The Poisson fluctuation dominates in the number count of the mass ratio to the host of $\sim {\cal O}(10^{-2})$, where the intrinsic scatter is smaller by a factor of a few. The host-mass scatter around its mean does not affect the subhalo mass function. Different models of the tidal evolution predict a factor of ∼2 difference in numbers of subhaloes with $\lesssim {\cal O}(10^{-5})$, while the dependence of the Poisson fluctuation on the tidal evolution models is subtle. The scheme provides a new tool for investigating the smallest scale structures of our Universe which are to be observed in near future experiments.

Other Link： https://academic.oup.com/mnras/article-pdf/517/2/2728/46561854/stac2857.pdf

Impacts of new small-scale N-body simulations on dark matter annihilations constrained from cosmological 21-cm line observations

Nagisa Hiroshima,Kazunori Kohri,Toyokazu Sekiguchi,Ryuichi Takahashi

Physical Review D   104 ( 8 )   2021.10  [Reviewed]  [Invited]

DOI arXiv

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Authorship：Corresponding author   Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：American Physical Society (APS)   Joint Work  

We revisit constraints on annihilating dark matter based on the global 21cm
signature observed by EDGES. For this purpose, we used the numerical data of
the latest N-body simulation performed by state-of-the-art standard in order to
estimate the boost factor at high redshifts ($z$ = 10 - 100), which enhances
the annihilation of dark matter in course of structure formation. By taking
into account to what fraction injected energy from dark matter annihilation
contributes to ionization, excitation and heating of intergalactic medium
during dark ages, we estimated how large the global 21cm absorption can be. By
assuming the thermal freezeout scenario, we find that $m_{\rm DM} < 15$ GeV and
$m_{\rm DM} < 3$ GeV have been excluded at 95$\%$ C.L. for the annihilation
modes into $b\bar{b}$ and $e^+ e^-$, respectively.

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.104.083547/fulltext

Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation

The Cherenkov Telescope Array Consortium,:,H. Abdalla,H. Abe,F. Acero,A. Acharyya,R. Adam,I. Agudo, … Show more authors

Journal of Cosmology and Astroparticle Physics   2021 ( 2 )   48 - 48   2020.10  [Reviewed]  [Invited]

DOI arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：IOP Publishing   Joint Work  

The Cherenkov Telescope Array (CTA), the new-generation ground-based
observatory for $\gamma$-ray astronomy, provides unique capabilities to address
significant open questions in astrophysics, cosmology, and fundamental physics.
We study some of the salient areas of $\gamma$-ray cosmology that can be
explored as part of the Key Science Projects of CTA, through simulated
observations of active galactic nuclei (AGN) and of their relativistic jets.
Observations of AGN with CTA will enable a measurement of $\gamma$-ray
absorption on the extragalactic background light with a statistical uncertainty
below 15% up to a redshift $z=2$ and to constrain or detect $\gamma$-ray halos
up to intergalactic-magnetic-field strengths of at least 0.3pG. Extragalactic
observations with CTA also show promising potential to probe physics beyond the
Standard Model. The best limits on Lorentz invariance violation from
$\gamma$-ray astronomy will be improved by a factor of at least two to three.
CTA will also probe the parameter space in which axion-like particles could
constitute a significant fraction, if not all, of dark matter. We conclude on
the synergies between CTA and other upcoming facilities that will foster the
growth of $\gamma$-ray cosmology.

Other Link： http://arxiv.org/pdf/2010.01349v2

Pre-construction estimates of the Cherenkov Telescope Array sensitivity to a dark matter signal from the Galactic centre

The Cherenkov Telescope Array Consortium,:,A. Acharyya,R. Adam,C. Adams,I. Agudo,A. Aguirre-Santae … Show more authors

Journal of Cosmology and Astroparticle Physics   2021 ( 1 )   2020.7

DOI Scopus arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Joint Work  

We provide an updated assessment of the power of the Cherenkov Telescope
Array (CTA) to search for thermally produced dark matter at the TeV scale, via
the associated gamma-ray signal from pair-annihilating dark matter particles in
the region around the Galactic centre. We find that CTA will open a new window
of discovery potential, significantly extending the range of robustly testable
models given a standard cuspy profile of the dark matter density distribution.
Importantly, even for a cored profile, the projected sensitivity of CTA will be
sufficient to probe various well-motivated models of thermally produced dark
matter at the TeV scale. This is due to CTA's unprecedented sensitivity,
angular and energy resolutions, and the planned observational strategy. The
survey of the inner Galaxy will cover a much larger region than corresponding
previous observational campaigns with imaging atmospheric Cherenkov telescopes.
CTA will map with unprecedented precision the large-scale diffuse emission in
high-energy gamma rays, constituting a background for dark matter searches for
which we adopt state-of-the-art models based on current data. Throughout our
analysis, we use up-to-date event reconstruction Monte Carlo tools developed by
the CTA consortium, and pay special attention to quantifying the level of
instrumental systematic uncertainties, as well as background template
systematic errors, required to probe thermally produced dark matter at these
energies.

Other Link： http://arxiv.org/pdf/2007.16129v2

Search for Gamma-Ray Signals from Dark Matter Annihilations in Extended Dwarf Spheroidal Galaxies

Nagisa Hiroshima

The Astronomical Herald   113 ( 2 )   2020.2  [Reviewed]  [Invited]

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Single Work  

CTA Report 159: General Report

Kubo Hidetoshi,Inada Tomohiro,Hara Satoshi,Harada Yoshiki,Bamba Aya,Hiroshima Nagisa,Hirotani Koui … Show more authors

Meeting Abstracts of the Physical Society of Japan   75   439 - 439   2020

DOI

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Joint Work  

MeV-scale reheating temperature and thermalization of oscillating neutrinos by radiative and hadronic decays of massive particles

Takuya Hasegawa,Nagisa Hiroshima,Kazunori Kohri,Rasmus S. L. Hansen,Thomas Tram,Steen Hannestad

Journal of Cosmology and Astroparticle Physics   2019.8

DOI arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Joint Work  

From a theoretical point of view, there is a strong motivation to consider an
MeV-scale reheating temperature induced by long-lived massive particles with
masses around the weak scale, decaying only through gravitational interaction.
In this study, we investigate lower limits on the reheating temperature imposed
by big-bang nucleosynthesis assuming both radiative and hadronic decays of such
massive particles. For the first time, effects of neutrino self-interactions
and oscillations are taken into account in the neutrino thermalization
calculations. By requiring consistency between theoretical and observational
values of light element abundances, we find that the reheating temperature
should conservatively be $T_{\rm RH} \gtrsim 1.8$ MeV in the case of the 100%
radiative decay, and $T_{\rm RH} \gtrsim$ 4-5 MeV in the case of the 100%
hadronic decays for particle masses in the range of 10 GeV to 100 TeV.

Other Link： http://arxiv.org/pdf/1908.10189v2

Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout

A. Acharyya,I. Agudo,E. O. Angüner,R. Alfaro,J. Alfaro,C. Alispach,R. Aloisio,R. Alves Batista,J. - … Show more authors

Astroparticle Physics   111   35 - 53   2019.4  [Reviewed]  [Invited]

DOI arXiv

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：Elsevier BV   Joint Work  

The Cherenkov Telescope Array (CTA) is the major next-generation observatory
for ground-based very-high-energy gamma-ray astronomy. It will improve the
sensitivity of current ground-based instruments by a factor of five to twenty,
depending on the energy, greatly improving both their angular and energy
resolutions over four decades in energy (from 20 GeV to 300 TeV). This
achievement will be possible by using tens of imaging Cherenkov telescopes of
three successive sizes. They will be arranged into two arrays, one per
hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We
present here the optimised and final telescope arrays for both CTA sites, as
well as their foreseen performance, resulting from the analysis of three
different large-scale Monte Carlo productions.

Other Link： http://arxiv.org/pdf/1904.01426v1

Halo Substructure Boosts to the Signatures of Dark Matter Annihilation

[Shin'ichiro Ando,Tomoaki Ishiyama,Nagisa Hiroshima

MDPI journals   2019.3  [Reviewed]  [Invited]

DOI arXiv

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Joint Work  

The presence of dark matter substructure will boost the signatures of dark
matter annihilation. We review recent progress on estimates of this subhalo
boost factor---a ratio of the luminosity from annihilation in the subhalos to
that originating the smooth component---based on both numerical $N$-body
simulations and semi-analytic modelings. Since subhalos of all the scales,
ranging from the Earth mass (as expected, e.g., the supersymmetric neutralino,
a prime candidate for cold dark matter) to galaxies or larger, give substantial
contribution to the annihilation rate, it is essential to understand subhalo
properties over a large dynamic range of more than twenty orders of magnitude
in masses. Even though numerical simulations give the most accurate assessment
in resolved regimes, extrapolating the subhalo properties down in sub-grid
scales comes with great uncertainties---a straightforward extrapolation yields
a very large amount of the subhalo boost factor of $\gtrsim$100 for galaxy-size
halos. Physically motivated theoretical models based on analytic prescriptions
such as the extended Press-Schechter formalism and tidal stripping modeling,
which are well tested against the simulation results, predict a more modest
boost of order unity for the galaxy-size halos. Giving an accurate assessment
of the boost factor is essential for indirect dark matter searches and thus,
having models calibrated at large ranges of host masses and redshifts, is
strongly urged upon.

Other Link： http://arxiv.org/pdf/1903.11427v2

Constraints on small-scale primordial power by annihilation signals from extragalactic dark matter minihalos

Tomohiro Nakama,Teruaki Suyama,Kazunori Kohri,Nagisa Hiroshima

Physical Review D   97 ( 2 )   2017.12  [Reviewed]  [Invited]

DOI Scopus arXiv

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：American Physical Society   Joint Work  

We revisit constraints on small-scale primordial power from annihilation
signals from dark matter minihalos. Using gamma rays and neutrinos from
extragalactic minihalos and assuming the delta-function primordial spectrum, we
show the dependence of the constraints on annihilation modes, the mass of dark
matter, and the annihilation cross section. We report both conservative
constraints by assuming minihalos are fully destructed when becoming part of
halos originating from the standard almost-scale invariant primordial spectrum,
and optimistic constraints by neglecting destruction.

Other Link： http://arxiv.org/pdf/1712.08820v1