arXiv subjects

S. Matsumoto

Publications and source records attributed to S. Matsumoto.

At least 19 recordsLinked to original sources

arXiv2023

No-Go Theorems for Hairy Black Holes in Scalar- or Vector-Tensor-Gauss-Bonnet Theory

In this paper, we show a no-go theorem for static spherically symmetric black holes with vector hair in Einstein-$Λ$-Vector-Tensor-Gauss-Bonnet theory where a complex vector field non-minimally couples with Gauss-Bonnet invariant. For this purpose, we expand metric functions and radial functions of a vector field around the event horizon, and substitute the expansions into equations of motion. Demanding that the equations of motion are satisfied in each order, we show that the complex vector field vanishes on the event horizon. Moreover, when the event horizon is degenerated, it is also implied that the complex vector field vanishes on and outside the horizon.

gr-qc↗

arXiv2023

Kepler K2 Campaign 9: II. First space-based discovery of an exoplanet using microlensing

We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens--source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass--position--velocity degeneracy and measure the planet's mass directly. We find a host mass of $0.58\pm0.04 ~{\rm M}_\odot$ and a planetary mass of $1.1\pm0.1 ~{\rm M_J}$. The system lies at a distance of $5.2\pm0.2~$kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be $4.2\pm0.3~$au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}~$au and orbital period $P = 13^{+9}_{-2}~$yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models.

astro-ph.EP↗

arXiv2022

Precision measurement of a brown dwarf mass in a binary system in the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035

Context. Brown dwarfs are poorly understood transition objects between stars and planets, with several competing mechanisms having been proposed for their formation. Mass measurements are generally difficult for isolated objects but also for brown dwarfs orbiting low-mass stars, which are often too faint for spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here we present the analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is due to a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including parallax, source radius and orbital motion of the binary lens. Results. After accurate modeling, we find that the lens is composed of a red dwarf with mass $M_1 = 0.149 \pm 0.010M_\odot$ and a brown dwarf with mass $M_2 = 0.0463 \pm 0.0031M_\odot$, at a projected separation of $a_\perp = 0.585$ au. The system has a peculiar velocity that is typical of old metal-poor populations in the thick disk. Percent precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become common with the Roman space telescope.

astro-ph.SR↗

arXiv2022

Differential cross sections and photon beam asymmetries of $η$ photoproduction on the proton at $E_γ$ = 1.3-2.4 GeV

We have carried out exclusive measurements for the photoproduction of an $η$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $γp \to ηp$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0 < \cos{θ^η_{\mathrm{c.m.}}} < 0.6$. The reaction is identified by selecting a proton and two $γ$'s produced by an $η$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $η$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $η$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.

nucl-ex↗

arXiv2015

Physics at the e+ e- Linear Collider

A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well.

hep-ph↗

arXiv2012

Quantification of group chasing and escaping process

We study a simple group chase and escape model by introducing new parameters with which configurations of chasing and escaping in groups are classified into three characteristic patterns. In particular, the parameters distinguish two essential configurations: a one-directional formation of chasers and escapees, and an escapee surrounded by chasers. In addition, pincer movements and aggregating processes of chasers and escapees are also quantified. Appearance of these configurations highlights efficiency of hunting during chasing and escaping.

physics.comp-ph↗

arXiv2011

A Simple Method of Calculating Effective Operators

It is important to obtain effective operators by integrating out high energy degrees of freedom in physics. We suggest a general method of calculating accurate irrelevant operators in a scattering process without use of equation of motions. By using this method, for example, we will represent a complete set of dimension six operators in QCD, which are induced from physics beyond the standard model, supersymmetry and universal extra dimension. We will also show an example of effective anomalous 4-Fermi interactions induced from a little Higgs model.

hep-ph↗

arXiv2011

Baryogenesis from Dark Sector

We propose a novel mechanism to generate a suitable baryon asymmetry from dark (hidden) sector. This is a Baryogenesis through a reverse pathway of the "asymmetric dark matter" scenario. In the mechanism, the asymmetry of dark matter is generated at first, and it is partially transferred into a baryon asymmetry in the standard model sector. This mechanism enables us not only to realize the generation of the baryon asymmetry but also to account for the correct amount of dark matter density in the present universe within a simple framework.

hep-ph↗

arXiv2010

Identification of new physics and general WIMP search at the ILC

We investigate the possibility of the identification of TeV physics models including WIMP dark matter at the International Linear Collider. Many TeV physics models contain a WIMP dark matter (chi^0) and charged new particle (chi^{pm}) which interacts with the WIMP dark matter via the vertex chi^{pm} chi^0 W^{mp}. Through Monte Carlo simulations, we study the process, e^+e^- to chi^+ chi^- to chi^0 chi^0 W^+ W^-, because the signal contains the fruitful information of the model. We show that, in particular, the distribution of the chi^{pm} production angle is the powerful probe in the TeV physics model search.

hep-ph↗

arXiv2010

Simulation Study of W Boson + Dark Matter Signatures for Identification of New Physics

Identification of beyond-standard-models including WIMP dark matter is studied in four particle final state with a W boson pair and a WIMP pair at the International Linear Collider. Models with different spin structures give distinguishable production angle distributions. After the mass determination in each model, the production angle is reconstructed using the four momentum of W bosons with a back-to-back constraint. Three models of Inert Higgs, Supersymmetry and Little Higgs are considered. Discrimination power at 200 fb and 40 fb signal cross section with 500 fb-1 luminosity at sqrt(s) = 500 GeV is obtained.

hep-ex↗

arXiv2007

Compensation of the Crossing Angle with Crab Cavities at KEKB

Crab cavities have been installed in the KEKB B--Factory rings to compensate the crossing angle at the collision point and thus increase luminosity. The beam operation with crab crossing has been done since February 2007. This is the first experience with such cavities in colliders or storage rings. The crab cavities have been working without serious issues. While higher specific luminosity than the geometrical gain has been achieved, further study is necessary and under way to reach the prediction of simulation.

physics.ins-det↗

arXiv2004

Multiple finite Riemann zeta functions

Observing a multiple version of the divisor function we introduce a new zeta function which we call a multiple finite Riemann zeta function. We utilize some $q$-series identity for proving the zeta function has an Euler product and then, describe the location of zeros. We study further multi-variable and multi-parameter versions of the multiple finite Riemann zeta functions and their infinite counterparts in connection with symmetric polynomials and some arithmetic quantities called powerful numbers.

math.NT↗

arXiv2000

Vacuum Structure of Twisted Scalar Field Theories on M^{D-1} \otimes S^1

We study scalar field theories on M^{D-1} \otimes S^1, which allow to impose twisted boundary conditions for the S^1 direction, in detail and report several interesting properties overlooked so far. One of characteristic features is the appearance of critical radii of the circle S^1. A phase transition can occur at the classical level or can be caused by quantum effects. Radiative corrections can restore broken symmetries or can break symmetries for small radius. A surprising feature is that the translational invariance for the S^1 direction can spontaneously be broken. A particular class of coordinate-dependent vacuum configurations is clarified and the O(N) ϕ^4 model on M^{D-1}\otimes S^1 is extensively studied, as an illustrative example.

hep-th↗

arXiv1996

One Loop Supersymmetric QCD Radiative Corrections to the top quark production in $p\bar{p}$ collisions

The purpose of this note is to give the one loop radiative corrections to the top quark pair production in the $p\bar{p}$ annihilation at the Fermilab Tevatron in the context of the Minimal Supersymmetric Model. We concentrate here on the supersymmetric QCD corrections and give the analytic expression for these corrections. Recently Li et. al. have reported the supersymmetric QCD corrections to this process we indicate clearly a comparison of their and our work. In particular, we find additional corrections [crossed box and gluon self-energy] at the one loop level which are not given by Li et. al.. Our numerical results disagree with the original claim of Li et. al. The numerical values given by them in a recent erratum do agree with the general trend of our numerical results however the actual values still disagree. We find that the percentage corrections at the hadronic corrections changes from $22\%$ to $-0.5\%$ as the squark mass is changed from 100 GeV to 600 GeV, for a gluino mass of 200 GeV. For a gluino mass of 150 GeV the squark-mass dependence is less abrupt; they change from $-5.3\%$ to $1\%$ as the squark mass is varied between 100 GeV and 600 GeV. We also present numerical results for differential cross section at the hadronic level, and percentage corrections at the parton level. PACS number(s): 14.80Dq; 12.38Bx; 14.80. Gt

hep-ph↗

arXiv1995

Supersymmetric contribution to the quark-lepton universality violation in charged currents

The supersymmetric one-loop contribution to the quark-lepton universality violation in the low-energy charged current weak interactions is studied. It is shown that the recent experimental data with the 1-$σ$ deviation from the universality may be explained by the existence of the light sleptons ($<220$GeV) and relatively light chargino and neutralinos ($<600$GeV) with significant gaugino components. The sign of the universality violation is briefly discussed.

hep-ph↗

arXiv1995

Constraints on New Physics in the Electroweak Bosonic Sector from Current Data and Future Experiments

Extensions of the Standard Model which involve a new scale, $Λ$, may, for energies sufficiently small compared to this new scale, be expressed in terms of operators with energy dimension greater than four. The coefficients of just four SU(2)$\times$U(1)-gauge-invariant energy-dimension-six operators are sufficient to parameterize the contributions of new physics in the electroweak bosonic sector to electroweak precision measurements. In this letter we update constraints on the coefficients of these four operators due to recent precision measurements of electroweak observables. We further demonstrate how such constraints may be improved by experiments at TRISTAN, LEP2 and at a future linear $e^+e^-$ collider. The relationship of these operators to the oblique parameters $S$, $T$ and $U$ is examined. Two of the operators contribute to a non-standard running of the electroweak charge form-factors $\overlineα(q^2)$, $\overline{s}^2(q^2)$, $\overline{g}_Z^2(q^2)$ and $\overline{g}_W^2(q^2)$; in the special case where the coefficients of these two vanish the operator analysis reduces to an analysis in terms of $S$, $T$ and $U$ with $U = 0$.

hep-ph↗

arXiv1994

Novel Approach to Confront Electroweak Data and Theory

A novel approach to study electroweak physics at one-loop level in generic ${\rm SU(2)_L \times U(1)_Y}$ theories is introduced. It separates the 1-loop corrections into two pieces: process specific ones from vertex and box contributions, and universal ones from contributions to the gauge boson propagators. The latter are parametrized in terms of four effective form factors $\bar{e}^2(q^2)$, $\bar{s}^2(q^2)$, $\bar{g}_Z^2(q^2)$ and $\bar{g}_W^2 (q^2)$ corresponding to the $γγ$, $γZ$, $ZZ$ and $WW$ propagators. Under the assumption that only the Standard Model contributes to the process specific corrections, the magnitudes of the four form factors are determined at $q^2=0$ and at $q^2=\mmz$ by fitting to all available precision experiments. These values are then compared systematically with predictions of ${\rm SU(2)_L \times U(1)_Y}$ theories. In all fits $α_s(\mz)$ and $\barα(\mmz)$ are treated as external parameters in order to keep the interpretation as flexible as possible. The treatment of the electroweak data is presented in detail together with the relevant theoretical formulae used to interpret the data. No deviation from the Standard Model has been identified. Ranges of the top quark and Higgs boson masses are derived as functions of $α_s(\mz)$ and $\barα(\mmz)$. Also discussed are consequences of the recent precision measurement of the left-right asymmetry at SLC as well as the impact of a top quark mass and an improved $W$ mass measurement.

hep-ph↗

arXiv1993

Electroweak Radiative Corrections

A new framework to study electroweak physics at one-loop level in general ${\rm SU(2)_L \times U(1)_Y}$ theories is introduced. It separates the 1-loop corrections into two pieces: process specific ones from vertex and box contributions and the universal ones due to contributions to the gauge boson propagators. The latter are parametrized in terms of four effective form factors, $\bar{e}^2(q^2)$, $\bar{s}^2(q^2)$, $\bar{g}_Z^2(q^2)$, and $\bar{g}_W^2(q^2)$, correspondingly to $γγ$, $γZ$, $ZZ$, and $WW$ propagators. By assuming only the standard model contributions to the process specific corrections, the magnitudes of the four form factors are determined at $q^2=0$ and at $q^2=m_Z^2$ from all available precision experiments. These values are then compared systematically with the predictions of the ${\rm SU(2)_L \times U(1)_Y}$ theories. No deviation from the standard model has been identified. Plausible range of the top quark mass is then obtained for a given Higgs boson mass and $α_s$ .

hep-ph↗