arXiv subjects

Shin Sasaki

Publications and source records attributed to Shin Sasaki.

At least 109 records · Page 6Linked to original sources

arXiv2007

Deformation of Super Yang-Mills Theories in R-R 3-form Background

We study deformation of N=2 and N=4 super Yang-Mills theories, which are obtained as the low-energy effective theories on the (fractional) D3-branes in the presence of constant Ramond-Ramond 3-form background. We calculate the Lagrangian at the second order in the deformation parameter from open string disk amplitudes. In N=4 case we find that all supersymmetries are broken for generic deformation parameter but part of supersymmetries are unbroken for special case. We also find that classical vacua admit fuzzy sphere configuration. In N=2 case we determine the deformed supersymmetries. We rewrite the deformed Lagrangians in terms of N=1 superspace, where the deformation is interpreted as that of coupling constants.

hep-th↗

arXiv2007

Radial profile and log-normal fluctuations of intra-cluster medium as an origin of systematic bias of spectroscopic temperature

The origin of the recently reported systematic bias in the spectroscopic temperature of galaxy clusters is investigated using cosmological hydrodynamical simulations. We find that the local inhomogeneities of the gas temperature and density, after corrected for the global radial profiles, have nearly a universal distribution that resembles the log-normal function. Based on this log-normal approximation for the fluctuations in the intra-cluster medium, we develop an analytical model that explains the bias in the spectroscopic temperature discovered recently. We conclude that the multi-phase nature of the intra-cluster medium not only from the radial profiles but also from the local inhomogeneities plays an essential role in producing the systematic bias.

astro-ph↗

arXiv2006

Deformation of N=4 Super Yang-Mills Theory in Graviphoton Background

We study deformation of N=4 super Yang-Mills theory from type IIB superstrings with D3-branes in the constant R-R background. We compute disk amplitudes with one graviphoton vertex operator and investigate the zero-slope limit of the amplitudes. We obtain the effective action deformed by the graviphoton background, which contains the one defined in non(anti)commutative N=1 superspace as special case. The bosonic part of the Lagrangian gives the Chern-Simons term coupled with the R-R potential. We study the vacuum configuration of the deformed Lagrangian and find the fuzzy sphere configuration for scalar fields.

hep-th↗

arXiv2006

Non(anti)commutative N=2 Supersymmetric Gauge Theory from Superstrings in the Graviphoton Background

We study open string amplitudes with the D3-branes in type IIB superstring theory compactified on C^2/Z_2. We introduce constant graviphoton background along the branes and calculate disk amplitudes using the NSR formalism. We take the zero slope limit and investigate the effective Lagrangian on the D3-branes deformed by the graviphoton background. We find that the deformed Lagrangian agrees with that of N=2 supersymmetric U(N) gauge theory defined in non(anti)commutative N=1 superspace by choosing appropriate graviphoton background. It is also shown that abelian gauge theory defined in N=2 harmonic superspace with specific non-singlet deformation is consistent with the deformed theory.

hep-th↗

arXiv2006

Soft X-ray Transmission Spectroscopy of Warm/Hot Intergalactic Medium with XEUS

We discuss the detectability of Warm/Hot Intergalactic medium (WHIM) via the absorption lines toward bright point sources with a future X-ray satellite mission, XEUS. While we consider bright QSOs as specific examples, the methodology can be applied to bright GRB afterglows. We create mock absorption spectra for bright QSOs (more than 20 QSOs over the all sky) using a light-cone output of a cosmological hydrodynamic simulation. We assume that WHIM is under collisional and photo-ionization equilibrium. If WHIM has a constant metallicity of $Z=0.1Z_\odot$, approximately 2 O{\sc vii} absorption line system with $>3σ$ will be detected on average along a random line-of-sight toward bright QSOs up to $z=0.3$ for 30 ksec exposure.

astro-ph↗

arXiv2006

Non-equilibrium Ionization State of Warm-Hot Intergalactic Medium

Time evolution of the ionization state of metals in the cosmic baryons is investigated in a cosmological context without the assumption of ionization equilibrium. We find that a significant fraction of ionized oxygen ions (OVII and OVIII) in the warm-hot intergalactic medium (WHIM) is not in the ionization equilibrium state at a redshift of z~0. We also investigate the effect on the detectability and observables of WHIM as a consequence of such deviation from ionization equilibrium. It is found that the detectability of WHIM is not altered very much both through its emission and absorption signatures, but line ratios between OVII and OVIII are significantly different from those in the ionization equilibrium state.

astro-ph↗

arXiv2006

Systematic bias in the estimate of cluster mass and the fluctuation amplitude from cluster abundance statistics

We revisit the estimate of the mass fluctuation amplitude, sigma_8, from the observational X-ray cluster abundance. In particular, we examine the effect of the systematic difference between the cluster virial mass estimated from the X-ray spectroscopy, M_{vir, spec}, and the true virial mass of the corresponding halo, M_{vir}. Mazzotta et al. (2004) recently pointed out the possibility that alpha_M = M_{vir, spec}/M_{vir} is systematically lower than unity. We perform the statistical analysis combining the latest X-ray cluster sample and the improved theoretical models and find that sigma_8 \sim 0.76 +/- 0.01 + 0.50 (1-alpha_M) for 0.5 \le alpha_M \le 1, where the quoted errors are statistical only. Thus if alpha_M \sim 0.7, the value of sigma_8 from cluster abundance alone is now in better agreement with other cosmological data including the cosmic microwave background, the galaxy power spectrum and the weak lensing data. The current study also illustrates the importance of possible systematic effects in mapping real clusters to underlying dark halos which changes the interpretation of cluster abundance statistics.

astro-ph↗

arXiv2005

Non-local Wess-Zumino Model on Nilpotent Noncommutative Superspace

We investigate the theory of the bosonic-fermionic noncommutativity, $[x^μ,θ^α] = i λ^{μα}$, and the Wess-Zumino model deformed by the noncommutativity. Such noncommutativity links well-known space-time noncommutativity to superspace non-anticommutativity. The deformation has the nilpotency. We can explicitly evaluate noncommutative effect in terms of new interactions between component fields. The interaction terms that have Grassmann couplings are induced. The noncommutativity does completely break full $\mathcal{N}=1$ supersymmetry to $ \mathcal{N} = 0 $ theory in Minkowski signature. Similar to the space-time noncommutativity, this theory has higher derivative terms and becomes non-local theory. However this non-locality is milder than the space-time noncommutative field theory. Due to the nilpotent feature of the coupling constants, we find that there are only finite number of Feynman diagrams that give noncommutative corrections at each loop order.

hep-th↗

arXiv2005

Lorentz invariant and supersymmetric interpretation of noncommutative quantum field theory

In this paper, using a Hopf-algebraic method, we construct deformed Poincaré SUSY algebra in terms of twisted (Hopf) algebra. By adapting this twist deformed super-Poincaré algrebra as our fundamental symmetry, we can see the consistency between the algebra and non(anti)commutative relation among (super)coordinates and interpret that symmetry of non(anti)commutative QFT is in fact twisted one. The key point is validity of our new twist element that guarantees non(anti)commutativity of space. It is checked in this paper for N=1 case. We also comment on the possibility of noncommutative central charge coordinate. Finally, because our twist operation does not break the original algebra, we can claim that (twisted) SUSY is not broken in contrast to the string inspired $\mathcal{N}=1/2$ SUSY in N=1 non(anti)commutative superspace.

hep-th↗

arXiv2004

SU(2)xU(1) non-anticommutative N=2 supersymmetric gauge theory

We derive the master function governing the component action of the four-dimensional non-anticommutative (NAC) and fully N=2 supersymmetric gauge field theory with a non-simple gauge group U(2)=SU(2)xU(1). We use a Lorentz singlet NAC-deformation parameter and an N=2 supersymmetric star (Moyal) product which do not break any of the fundamental symmetries of the undeformed N=2 gauge theory. The scalar potential in the NAC-deformed theory is calculated. We also propose the non-abelian BPS-type equations in the case of the NAC-deformed N=2 gauge theory with the SU(2) gauge group, and comment on the SU(3) case too. The NAC-deformed field theories can be thought of as the effective (non-perturbative) N=2 gauge field theories in a certain (scalar only) N=2 supergravity background.

hep-th↗

arXiv2004

Non-anticommutative N=2 supersymmetric SU(2) gauge theory

We calculate the component Lagrangian of a four-dimensional non-anticommutative (with a singlet deformation parameter) and fully N=2 supersymmetric gauge field theory with the simple gauge group SU(2). We find that the deformed (classical) scalar potential is unbounded from below, in contrast to the undeformed case.

hep-th↗

arXiv2004

BPS-type equations in the non-anticommutative N=2 supersymmetric U(1) gauge theory

We investigate the equations of motion in the four-dimensional non-anticommutative N=2 supersymmetric U(1) gauge field theory, in the search for BPS configurations. The BPS-like equations, generalizing the abelian (anti)self-duality conditions, are proposed. We prove full solvability of our BPS-like equations, as well their consistency with the equations of motion. Certain restrictions on the allowed scalar field values are also found. Surviving supersymmetry is briefly discussed too.

hep-th↗

arXiv2004

Searching for cosmic missing baryons with DIOS -- Diffuse Intergalactic Oxygen Surveyor --

Approximately 30 to 50 percent of the total baryons in the present universe is supposed to take a form of warm/hot intergalactic medium (WHIM) whose X-ray continuum emission is very weak. In order to carry out a direct and homogeneous survey of elusive cosmic missing baryons, we propose a dedicated soft-X-ray mission, {\it DIOS} (Diffuse Intergalactic Oxygen Surveyor). The unprecedented energy resolution ($\sim 2$eV) of the XSA (X-ray Spectrometer Array) on-board {\it DIOS} enables us to identify WHIM with gas temperature $T=10^{6-7}$K and overdensity $δ=10-100$ located at $z<0.3$ through emission lines of O{\sc vii} and O{\sc viii}. {\it DIOS}, hopefully launched in several years, promises to open a new window of detection and characterization of cosmic missing baryons, and to provide yet another important and complementary tool to trace the large-scale structure of the universe.

astro-ph↗

arXiv2003

Monte-Carlo Modeling of Non-Gravitational Heating Processes in Galaxy Clusters

We consider non-gravitational heating effects on galaxy clusters on the basis of the Monte-Carlo modeling of merging trees of dark matter halos combined with the thermal evolution of gas inside each halo. Under the assumption of hydrostatic equilibrium and the isothermal gas profiles, our model takes account of the metallicity evolution, metallicity-dependent cooling of gas, supernova energy feedback, and heating due to jets of radio galaxies in a consistent manner. The observed properties of galaxy clusters can be explained in models with higher non-gravitational heating efficiency than that in the conventional model. Possibilities include jet heating by the Fanaroff-Riley Type II radio galaxies, and the enhanced star formation efficiency and/or supernova energy feedback, especially at high redshifts.

astro-ph↗

arXiv2003

Mass-temperature relation of galaxy clusters: implications from the observed luminosity-temperature relation and X-ray temperature function

We derive constraints on the mass-temperature relation of galaxy clusters from their observed luminosity-temperature relation and X-ray temperature function. Adopting the isothermal gas in hydrostatic equilibrium embedded in the universal density profile of dark matter halos, we compute the X-ray luminosity for clusters as a function of their hosting halo mass. We find that in order to reproduce the two observational statistics, the mass-temperature relation is very tightly constrained as T_{gas} = (1.5~2.0)keV (M_{vir}/10^{14}h_{70}^{-1}M_\odot)^{0.5~0.55}, and a simple self-similar evolution model (T_{gas} \propto M_{vir}^{2/3}) is strongly disfavored. In the cosmological model that we assume (a ΛCDM universe with Ω_0=0.3, λ_0=0.7 and h_{70}=1), the derived mass-temperature relation suggests that the mass fluctuation amplitude σ_8 is 0.7--0.8.

astro-ph↗

arXiv2002

Reliability of merger tree realizations of dark halos in the Monte-Carlo modeling of galaxy formation

We examine the reliability of the merger trees generated for the Monte-Carlo modeling of galaxy formation. In particular we focus on the cold gas fraction predicted from the merger trees with different assumptions on the progenitor distribution function, the timestep, and the mass resolution. We show that the cold gas fraction is sensitive to the accuracy of the merger trees at small-mass scales of progenitors at high redshifts. One can reproduce the Press-Schechter prediction to a reasonable degree by adopting a fairly large number of redshift bins, N_{step} ~ 1000 in generating merger trees, which is a factor of ten larger than the canonical value used in previous literature.

astro-ph↗

arXiv2002

Scaling Relation to Understand Non-Detection of Cold Gas at the Cluster Center

Recent XMM-Newton observations of clusters of galaxies have indicated the soft X-ray spectra to be inconsistent with the simple isobaric cooling flow model. There is almost no feature of the cold gas expected from the model. This shows that we have not yet understood the physics of the hot gas in clusters of galaxies well. A quantitative evaluation of the behavior of gas cooling is important not only for understanding the clusters, themselves, but also for studying cosmology and galaxy formation. To clarify the problem of this reported discrepancy, we have studied scaling relations for clusters of galaxies based on the self-similarity assumption. We also propose an observational strategy to solve this problem.

astro-ph↗

arXiv2001

Heating of the Hot Intergalactic Medium by Powerful Radio Galaxies and Associated High Energy Gamma-Ray Emission

There is increasing evidence that some heating mechanism in addition to gravitational shock heating has been important for the hot gas inside clusters and groups of galaxies, as indicated by their observed X-ray scaling properties. While supernovae are the most obvious candidate heating sources, a number of recent studies have suggested that they may be energetically insufficient. Here we consider high-power, FRII radio galaxies and shock heating of the intracluster medium (ICM, including the case of the intergalactic medium prior to cluster formation) by their large-scale jets. Based on the observed statistics of radio galaxies in clusters and their evolution, along with the most reasonable assumptions, it is shown that they can provide the ICM with excess specific energies of 1--2 keV per particle, mainly during the redshift interval $z \sim 1-3$. This naturally meets the requirements of cluster evolution models with non-gravitational feedback in accounting for the observed deviations in the X-ray luminosity-temperature relation. In contrast to supernovae, such large-scale jets deposit their energy directly into the low density ICM outside galaxies, and are much less susceptible to radiative losses. As a clear and potentially decisive test of this scenario, we propose the observation of `prompt' high energy gamma-rays emitted by shock-accelerated, non-thermal electrons during the epoch of ICM heating by radio galaxies, which may be feasible with the {\it GLAST} satellite. Implications for recent detections of excess hard X-rays from groups are also discussed.

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