Last updated: Jan 1, 2019 at 09:11

Name OHTA Nobuyoshi Kindai University Faculty of Science and Engineering　Department of Science Associate Professor (BLANK)(The University of Tokyo), (BLANK)(The University of Tokyo)

## Research Areas

Apr 2006
-
Today
Professor, Faculty of Science and Engineering, Kindai University

Apr 1994
-
Mar 2006
Associate Professor, Faculty of Science, Osaka University

Dec 1990
-
Mar 1994
Associate Professor, College of general Education, Osaka University

Apr 1988
-
Nov 1990
Lecturer, College of general Education, Osaka University

Oct 1983
-
Mar 1988
Assistant Professor, College of general Education, Osaka University

## Published Papers

G. P. De Brito, N. Ohta, A. D. Pereira, A. A. Tomaz and M. Yamada
Physical Review D   98(2) 026027-1-026027-25   Jul 2018   [Refereed]
N. Ohta, R. Percacci and A. D. Pereira
Physical Review D   97(2) 026007-1-026007-11   Apr 2018   [Refereed]
PTEP   2018(3) 033B02 (13pp)   Mar 2018   [Refereed]
R. de León Ardón, N. Ohta and R. Percacci
Physical Review D   97(2) 026007   Jan 2018   [Refereed]
Progress of Theoretical and Experimantal Physics   2017 033E02   Mar 2017   [Refereed]
Nobuyoshi Ohta, Roberto Percacci and Antonio D. Pereira
European Physcal Jounal C   77(9) 611   Oct 2016   [Refereed]
Phys. Rev. D   94(8,Pt.A) 20   Oct 2016   [Refereed]
Nobuyoshi Ohta, Roberto Percacci and Antonio D. Pereira
JHEP   06 115   Jun 2016   [Refereed]
Nobuyoshi Ohta, Roberto Percacci and Gian Paolo Vacca
European Physical Journal C   76(2) 1-18   Jan 2016   [Refereed]
Classical and Quantum Gravity   33(3)    Jan 2016   [Refereed]
We study the beta functions for four-dimensional conformal gravity using two different parametrizations of metric fluctuation, linear split and exponential parametrization. We find that after imposing the traceless conditions, the beta functions a...
Nobuyoshi Ohta, Roberto Percacci and Gian Paolo Vacca
Phys. Rev. D   92(6,Pt.A) 1-61501   Sep 2015   [Refereed]
JPS Conf. Proc.   7 010007-1-010007-5   2015   [Refereed][Invited]
Jour. High Energy Phys.   2014(6)    Jun 2014   [Refereed]
Prog. Theor. Exp. Phys.   2014(4) 043B04   Apr 2014   [Refereed]
Class. Quant. Grav.   31 015024   Jan 2014   [Refereed]
We derive the one-loop beta functions for a theory of gravity with generic action containing up to four derivatives. The calculation is done in arbitrary dimension and on an arbitrary background. The special cases of three, four, near four, five a...
Phys. Rev. D   88 064002   Jul 2013   [Refereed]
We study charged black hole solutions in Einstein-Maxwell-Gauss-Bonnet theory
with the dilaton field which is the low-energy effective theory of the
heterotic string. The spacetime is -dimensional and assumed to be static and
plane symmetric wi...
Phys. Lett. B   725 495-499   Jun 2013   [Refereed]
It has been suggested that higher-derivative gravity theories coupled to a
scalar field with shift symmetry may be an important candidate for a quantum
gravity. We show that this class of gravity theories are renormalizable in D =
3 and 4 dimensions.
Phys.Rev. D   86(10,Pt.A) 104016   Aug 2012   [Refereed]
We study charged black hole solutions in Einstein-Gauss-Bonnet theory with
the dilaton field which is the low-energy effective theory of the heterotic
string. The spacetime is D-dimensional and assumed to be static and spherically
symmetric with t...
Class.Quant.Grav.   29 205012   May 2012   [Refereed]
We study the quantum properties of the three-dimensional higher derivative
gravity. In particular we calculate the running of the gravitational and
cosmological constants. The flow of these couplings shows that there exist both
Gaussian and nontri...
Phys.Rev. D   85(10,Pt.A) 101501   Jan 2012   [Refereed]
It has been suggested that new massive gravity with higher order terms in the
curvature may be renormalizable and thus a candidate for renormalizable quantum
gravity. We show that three-dimensional gravity that contains quadratic scalar
curvature ...
Eur.Phys.J. C   72 1858   Nov 2011   [Refereed]
We study the Hawking radiation in a new class of black hole solutions in the
Einstein-Gauss-Bonnet theory. The black hole has been argued to have vanishing
mass and entropy, but finite Hawking temperature. To check if it really emits
Kei-ichi Maeda, Nobuyoshi Ohta, Ryo Wakebe
Eur.Phys.J. C   72 1949   Nov 2011   [Refereed]
We study cosmological solutions in the effective heterotic string theory with
-correction terms in string frame. It is pointed out that the
effective theory has an ambiguity via field redefinition and we analyze
generalized effective theo...
Class.Quant.Grav.   29 015002   Sep 2011   [Refereed]
We study the condition that the theory is unitary and stable in
three-dimensional gravity with most general quadratic curvature,
Lorentz-Chern-Simons and cosmological terms. We provide the complete
classification of the unitary theories around fla...
Li-Ming Cao, Oleg Evnin, Nobuyoshi Ohta
JHEP 1106:062,2011      Apr 2011   [Refereed]
We consider intersecting black branes with strong gravitational waves
propagating along their worldvolume in the context of supergravity theories.
Both near-horizon and space-filling gravitational wave modes are included in
our ansatz. The equatio...
Li-Ming Cao, Oleg Evnin, Nobuyoshi Ohta
JHEP 1104:105,2011      Jan 2011
We describe a large class of solutions in pure gravity, dilaton gravity and
supergravity corresponding to extended higher-dimensional black holes with
strong (non-linear) gravitational waves propagating along their worldvolume.
For pure gravity, t...
Kei-ichi Maeda, Nobuyoshi Ohta, Yukinori Sasagawa
Phys.Rev.D83:044051,2011      Dec 2010
We find that AdS spacetime with a non-trivial linear dilaton field is an
exact solution in the effective action of string theory, which is described by
gravity with the Gauss-Bonnet curvature terms coupled to a dilaton field in the
string frame. T...
Phys. Lett. B695:41-44,2011      Oct 2010
It has been suggested that the dark energy that explains the observed
accelerating expansion of the universe may arise due to the contribution to the
vacuum energy of the QCD ghost in a time-dependent background. The argument
uses a four-dimension...
Masato Minamitsuji, Nobuyoshi Ohta, Kunihito Uzawa
Phys.Rev.D82:086002,2010      Jul 2010
The recent discovery of an explicit dynamical description of p-branes makes
it possible to investigate the existence of intersection of such objects. We
generalize the solutions depending on the overall transverse space coordinates
and time to tho...
Kei-ichi Maeda, Masato Minamitsuji, Nobuyoshi Ohta, Kunihito Uzawa
Phys.Rev.D82:046007,2010      Jun 2010
We present a class of dynamical solutions in a D-dimensional gravitational
theory coupled to a dilaton, a form field strength, and a cosmological
constant. We find that for any D due to the presence of a cosmological
constant, the metric of soluti...
Prog.Theor.Phys.124:207-225,2010      Apr 2010
We study global structures of black hole solutions in Einstein gravity with
Gauss-Bonnet term coupled to dilaton in various dimensions. In particular we
focus on the problem whether the singularity is weakened due to the
Gauss-Bonnet term and dila...
Masato Minamitsuji, Nobuyoshi Ohta, Kunihito Uzawa
Mar 2010
We investigate the dynamical 3-form flux compactifications and their
implications for cosmology in our brane world in the six-dimensional
Nishino-Salam-Sezgin model, which is usually referred to as the Salam-Sezgin
model. We take the background of...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
Phys.Rev.D81:084012,2010      Feb 2010
In a recent paper [arXiv:1001.0785], Verlinde has shown that the Newton
gravity appears as an entropy force. In this paper we show how gravity appears
as entropy force in Einstein's equation of gravitational field in a general
spherically symmetri...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
Phys. Rev. D 81, 061501(R) (2010)      Jan 2010
In this note by use of the holographic principle together with the
equipartition law of energy and the Unruh temperature, we derive the Friedmann
equations of a Friedmann-Robertson-Walker universe.
Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabe, Ryo Wakebe
JHEP 1004:013,2010      Jan 2010
We construct a general family of supersymmetric solutions in time- and
space-dependent wave backgrounds in general supergravity theories describing
single and intersecting p-branes embedded into time-dependent dilaton-gravity
plane waves of an arb...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
JHEP 1004:082,2010      Nov 2009
We present a class of exact analytic and static, spherically symmetric black
hole solutions in the semi-classical Einstein equations with Weyl anomaly. The
solutions have two branches, one is asymptotically flat and the other
asymptotically de Sit...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
Phys.Rev.D81:024018,2010      Nov 2009
We present a class of new black hole solutions in -dimensional Lovelock
gravity theory. The solutions have a form of direct product , where , is a negative constant
curvature space, a...
Chiang-Mei Chen, Dmitri V. Gal'tsov, Nobuyoshi Ohta, Dmitry G. Orlov
Oct 2009
Small black holes in heterotic string theory have vanishing horizon area at
the supergravity level, but the horizon is stretched to the finite radius
geometry once higher curvature corrections are turned
on. This has been de...
Phys. Rev. D 81, 084061 (2010)      Oct 2009
We explore the relationship between the first law of thermodynamics and
gravitational field equation at a static, spherically symmetric black hole
horizon in Ho\v{r}ava-Lifshtiz theory with/without detailed balance. It turns
out that as in the cas...
Rong-Gen Cai, Li-Ming Cao, Ya-Peng Hu, Nobuyoshi Ohta
Phys.Rev.D80:104016,2009      Oct 2009
We study generalized Misner-Sharp energy in gravity in a spherically
symmetric spacetime. We find that unlike the cases of Einstein gravity and
Gauss-Bonnet gravity, the existence of the generalized Misner-Sharp energy
depends on a constrai...
Kei-ichi Maeda, Nobuyoshi Ohta, Yukinori Sasagawa
Phys.Rev.D80:104032,2009      Aug 2009
We present the black hole solutions and analyse their properties in the
superstring effective field theory with the Gauss-Bonnet curvature correction
terms. We find qualitative differences in our results from those obtained in
the truncated model ...
Prog.Theor.Phys.122:1477-1500,2010      Aug 2009
We study black hole solutions in the Einstein gravity with Gauss-Bonnet term,
the dilaton and a positive "cosmological constant" in various dimensions.
Physically meaningful black holes with a positive cosmological term are
obtained only for those...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
Phys.Lett.B679:504-509,2009      May 2009
By using the canonical Hamiltonian method, we obtain the mass and entropy of
the black holes with general dynamical coupling constant in Ho\v{r}
ava-Lifshitz Gravity. Regardless of whether the horizon is sphere, plane or
hyperboloid, we ...
Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
Phys.Rev.D80:024003,2009      Apr 2009
We find topological (charged) black holes whose horizon has an arbitrary
constant scalar curvature in Ho\v{r}ava-Lifshitz theory. Without loss of
generality, one may take and -1. The black hole solution is
Kei-ichi Maeda, Nobuyoshi Ohta, Kunihito Uzawa
JHEP 0906:051,2009      Mar 2009
We present dynamical intersecting brane solutions in higher-dimensional
gravitational theory coupled to dilaton and several forms. Assuming the forms
of metric, form fields, and dilaton field, we give a complete classification of
dynamical interse...
Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabe, Ryo Wakebe
JHEP 0906:036,2009      Mar 2009
We construct a fairy general family of supersymmetric solutions in time- and
space-dependent backgrounds in general supergravity theories. One class of the
solutions are intersecting brane solutions with factorized form of time- and
space-dependen...
Prog.Theor.Phys.121:959-981,2009      Feb 2009
We study black hole solutions in the Einstein-Gauss-Bonnet gravity with the
dilaton and a negative cosmological constant''. We derive the field equations
for the static spherically symmetric () and hyperbolically symmetric
() spacetim...
Rong-Gen Cai, Zhang-Yu Nie, Nobuyoshi Ohta, Ya-Wen Sun
Phys.Rev.D79:066004,2009      Jan 2009
We calculate the shear viscosity of field theories with gravity duals of
Gauss-Bonnet gravity with a non-trivial dilaton using AdS/CFT. We find that the
dilaton filed has a non-trivial contribution to the ratio of shear viscosity
over entropy dens...
Zong-Kuan Guo, Nobuyoshi Ohta, Takashi Torii
Prog.Theor.Phys.121:253-273,2009      Nov 2008
We study asymptotically AdS topological black hole solutions with k=0 (plane
symmetric) in the Einstein gravity with Gauss-Bonnet term, the dilaton and a
"cosmological constant" in various dimensions. We derive the field equations
for suitable ans...
Zong-Kuan Guo, Nobuyoshi Ohta, Takashi Torii
Prog.Theor.Phys.120:581-607,2008      Jun 2008
We study spherically symmetric, asymptotically flat black hole solutions in
the low-energy effective heterotic string theory, which is the Einstein gravity
with Gauss-Bonnet term and the dilaton, in various dimensions. We derive the
field equation...
Kazuharu Bamba, Nobuyoshi Ohta, Shinji Tsujikawa
Phys.Rev.D78:043524,2008      May 2008
We estimate the strength of large-scale magnetic fields produced during
inflation in the framework of Dirac-Born-Infeld (DBI) theories. This analysis
is sufficiently general in the sense that it covers most of conformal symmetry
breaking theories ...
JCAP0804:035,2008      Mar 2008
We investigate the cosmological evolution of the system of a
Dirac-Born-Infeld field plus a perfect fluid. We analyze the existence and
stability of scaling solutions for the AdS throat and the quadratic potential.
We find that the scaling solutio...
Rong-Gen Cai, Chiang-Mei Chen, Kei-ichi Maeda, Nobuyoshi Ohta, Da-Wei Pang
Phys.Rev.D77:064030,2008      Dec 2007
We discuss the entropy-area relation for the small black holes with higher
curvature corrections by using the entropy function formalism and field
redefinition method. We show that the entropy of small black hole is
proportional to its ho...
Kazuharu Bamba, Zong-Kuan Guo, Nobuyoshi Ohta
Prog.Theor.Phys.118:879-892,2007      Jul 2007
We study cosmological solutions in the low-energy effective heterotic string
theory, which is the Einstein gravity with Gauss-Bonnet term and the dilaton.
We show that the field equations are cast into an autonomous system for flat
internal and ex...
Phys.Rev.D76:106001,2007      Jul 2007
We study the confinement/deconfinement phase transition of holographic
AdS/QCD models by using Ricci flat black holes up to , which corresponds to the expansion correction in the
dual field theory to $\lambda... Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa Phys.Rev.D76:023508,2007 Feb 2007 We place observational constraints on a coupling between dark energy and dark matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the five-year Supernova Legacy Survey (SNLS), the cosmic microwave background (CMB) shift parameter... Dongsu Bak, Nobuyoshi Ohta, Paul K. Townsend JHEP 0703:013,2007 Dec 2006 We present new supersymmetric solutions of the Dirac-Born-Infeld equations for time-independent D2-branes, including a 1/2 supersymmetric dyonic' D2-brane and various 1/4 supersymmetric configurations that include twisted' supertubes, superfunne... Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa Phys.Rev.D75:023520,2007 Nov 2006 We discuss the realization of inflation and resulting cosmological perturbations in the low-energy effective string theory. In order to obtain nearly scale-invariant spectra of density perturbations and a suppressed tensor-to-scalar ratio, it is g... Nobuyoshi Ohta, Kamal L. Panigrahi Phys.Rev.D74:126003,2006 Oct 2006 We construct a family of supersymmetric solutions in time-dependent backgrounds in supergravity theories. One class of the solutions are intersecting brane solutions and another class are brane solutions in pp-wave backgrounds, and their intersect... Chiang-Mei Chen, Pei-Ming Ho, Ishwaree P. Neupane, Nobuyoshi Ohta, John E. Wang JHEP0611:044,2006 Sep 2006 In our earlier paper [JHEP 0310 (2003) 058], we considered higher dimensional cosmological models with hyperbolic spaces. In particular the eternal accelerating expansion was obtained by studying small perturbation around the critical non-accelera... Kazuyuki Furuuchi, Nobuyoshi Ohta Prog.Theor.Phys. 116 (2006) 601-604 Jul 2006 We give a simple proof of the no-ghost theorem in the critical bosonic string theory by using a similarity transformation. Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabe Phys.Rev. D74 (2006) 104002 Jul 2006 We construct a supersymmetric rotating black hole with asymptotically flat four-dimensional spacetime times a circle, by superposing an infinite number of BMPV black hole solutions at the same distance in one direction. The near horizon structure ... Hideo Kodama, Nobuyoshi Ohta Prog.Theor.Phys.116:295-318,2006 May 2006 We show that the diagonal light-like solution with 16 supersymmetries in eleven-dimensional supergravity derived in our previous paper (hep-th/0509173) can be generalised to non-diagonal solutions preserving the same number of supersymmetries. Thi... Rong-Gen Cai, Nobuyoshi Ohta Phys.Rev. D74 (2006) 064001 Apr 2006 The Lovelock gravity is a fascinating extension of general relativity, whose action consists of the dimensionally extended Euler densities. Compared to other higher order derivative gravity theories, the Lovelock gravity is attractive since it has... Takayuki Ishino, Nobuyoshi Ohta Phys.Lett.B638:105-109,2006 Mar 2006 A large class of time-dependent solutions with 1/2 supersymmetry were found previously. These solutions involve cosmic singularities at early time. In this paper, we study if matrix string description of the singularities in these solutions with b... Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta Phys.Lett.B639:354-361,2006 Mar 2006 Recently a five-dimensional Kaluza-Klein black hole solution with squashed horizon has been found in hep-th/0510094. The black hole spacetime is asymptotically locally flat and has a spatial infinity . By using "boundary... Zong-Kuan Guo, Nobuyoshi Ohta, Yuan-Zhong Zhang Mod.Phys.Lett.A22:883-890,2007 Mar 2006 We develop a theoretical method of constructing the scalar (quintessence or phantom) potential directly from the dimensionless dark energy function X(z), the dark energy density in units of its present value. We apply our method to two parametriza... Kenta Akune, Kei-ichi Maeda, Nobuyoshi Ohta Phys.Rev.D73:103506,2006 Feb 2006 We present a detailed study of inflationary solutions in M-theory with higher order quantum corrections. We first exhaust all exact and asymptotic solutions of exponential and power-law expansions in this theory with quartic curvature corrections,... Rong-Gen Cai, Nobuyoshi Ohta Phys.Rev.D73:106009,2006 Jan 2006 Recently,in a paper hep-th/0511197, it was found that non-commutative super Yang-Mills (NCSYM) theory with space-dependent noncommutativity can be formulated as a decoupling limit of open strings ending on D3-branes wrapping a Melvin universe supp... Dongsu Bak, Kyungyu Kim, Nobuyoshi Ohta JHEP0601:072,2006 Nov 2005 Using the covariant M5-brane action, we construct configurations corresponding to supertubes with three and four charges. We derive the BPS equations and study the full structure of the solutions. In particular, we find new solutions involving arb... Takayuki Ishino, Hideo Kodama, Nobuyoshi Ohta Phys.Lett.B631:68-73,2005 Sep 2005 Imposing the condition that there should be a null Killing spinor with all the metrics and background field strengths being functions of the light-cone coordinates, we find general 1/2 BPS solutions in D=11 supergravity, and discuss several exampl... Chiang-Mei Chen, Dmitri V. Gal'tsov, Nobuyoshi Ohta Phys.Rev. D72 (2005) 044029 Jun 2005 We construct the general static solution to the supergravity action containing gravity, the dilaton and a set of antisymmetric forms describing the intersecting branes delocalized in the relative transverse dimensions. The solution is obtained by ... Zong-Kuan Guo, Nobuyoshi Ohta, Yuan-Zhong Zhang Phys.Rev.D72:023504,2005 May 2005 We develop a theoretical method of constructing the quintessence potential directly from the effective equation of state function , which describes the properties of the dark energy. We apply our method to four parametrizations of equation o... Nobuyoshi Ohta Int.J.Mod.Phys. A20 (2005) 1-40 Nov 2004 We review the recent developments in obtaining accelerating cosmologies and/or inflation from higher-dimensional gravitational theories, in particular superstring theories in ten dimensions and M-theory in eleven dimensions. We first discuss why i... Kei-ichi Maeda, Nobuyoshi Ohta Phys.Rev. D71 (2005) 063520 Nov 2004 We study time-dependent solutions in M and superstring theories with higher order corrections. We first present general field equations for theories of Lovelock type with stringy corrections in arbitrary dimensions. We then exhaust all exact and a... Dongsu Bak, Yoshifumi Hyakutake, Seok Kim, Nobuyoshi Ohta Nucl.Phys. B712 (2005) 115-138 Jul 2004 We give a geometric interpretation of the entropy of the supertubes with fixed conserved charges and angular momenta in two different approaches using the DBI action and the supermembrane theory. By counting the geometrically allowed microstates, ... Kei-ichi Maeda, Nobuyoshi Ohta Phys.Lett. B597 (2004) 400-407 May 2004 We study inflationary solutions in the M-theory. Including the fourth-order curvature correction terms, we find three generalized de Sitter solutions, in which our 3-space expands exponentially. Taking one of the solutions, we propose an inflation... Dongsu Bak, Yoshifumi Hyakutake, Nobuyoshi Ohta Nucl.Phys. B696 (2004) 251-262 Apr 2004 We study possible deformations of BPS supertubes keeping their conserved charges fixed. We show that there is no flat direction to closed supertubes of circular cross section with uniform electric and magnetic fields, and also to open planar super... Yan-Gang Miao, Nobuyoshi Ohta Phys.Lett. B594 (2004) 218-226 Apr 2004 We give general intersecting brane solutions without assuming any restriction on the metric in supergravity coupled to a dilaton and antisymmetric tensor fields in arbitrary dimensions . The result is a general class of intersecting brane solut... Dongsu Bak, Michael Gutperle, Shinji Hirano, Nobuyoshi Ohta Phys.Rev. D70 (2004) 086004 Mar 2004 We study a class of dilatonic deformations of asymptotically AdS_5 X S^5 geometry analytically and numerically. The spacetime is non-supersymmetric and suffers from a naked singularity. We propose that the causality bound may serve as a criterion ... Chiang-Mei Chen, Pei-Ming Ho, Ishwaree P. Neupane, Nobuyoshi Ohta, John E. Wang JHEP 0310:058,2003 Jun 2003 We present a systematic study of accelerating cosmologies obtained from M/string theory compactifications of hyperbolic spaces with time-varying volume. A set of vacuum solutions where the internal space is a product of hyperbolic manifolds is fou... Nobuyoshi Ohta, Kamal L. Panigrahi, Sanjay Nucl.Phys. B674 (2003) 306-328; Erratum-ibid. B748 (2006) 309-332 Jun 2003 We derive intersecting brane solutions in pp-wave spacetime by solving the supergravity field equations explicitly. The general intersection rules are presented. We also generalize the construction to the non-extremal solutions. Both the extremal ... Nobuyoshi Ohta, Makoto Sakaguchi Phys.Rev. D69 (2004) 066006 May 2003 We examine Killing spinor equations of the general eleven-dimensional pp-wave backgrounds, which contain a scalar H(x^m,x^-) in the metric and a three-form \xi(x^m,x^-) in the flux. Considering non-harmonic extra Killing spinors, we show that if t... Nobuyoshi Ohta Prog.Theor.Phys.110:269-283,2003 Apr 2003 We study aspects of the accelerating cosmologies obtained from the compactification of vacuum solution and S2-branes of superstring/M theories. Parameter dependence of the resulting expansion of our universe and internal space is examined for all ... Nobuyoshi Ohta Phys.Rev.Lett.91:061303,2003 Mar 2003 We point out that the recently proposed model of a flat 4-dimensional universe with accelerated expansion in string/M-theory is a special case of time-dependent solutions that the author found under the name of S-branes.'' We also show that simi... Nobuyoshi Ohta Phys.Lett. B559 (2003) 270-278 Feb 2003 We find a new class of time-dependent brane solutions in supergravities in arbitrary dimensions . These are general intersecting light-like branes (null-branes), and their superposition and intersection rules are obtained. This is achieved by d... Yan-Gang Miao, Nobuyoshi Ohta JHEP 0304:010,2003 Jan 2003 By using the systematic approach of parent action method, we derive one Weyl-noninvariant and two Weyl-invariant actions of bosonic -branes () starting from the Nambu-Goto action, and establish the duality symmetries in this set of fou... Nobuyoshi Ohta Phys.Lett. B558 (2003) 213-220 Jan 2003 We give a model-independent derivation of general intersecting rules for spacelike branes (S-branes) in arbitrary dimensions . This is achieved by directly solving bosonic field equations for supergravity coupled to a dilaton and antisymmetric ... Rong-Gen Cai, Jian-Xin Lu, Nobuyoshi Ohta Phys.Lett.B551:178-186,2003 Oct 2002 We study noncommutative open string (NCOS) theories realized in string theory with time-dependent backgrounds. Starting from a noncommutative Yang-Mills theory (NCYM) with a constant space-space noncommutativity but in a time-dependent background ... Dongsu Bak, Nobuyoshi Ohta, Mohammad M. Sheikh-Jabbari JHEP 0209:048,2002 May 2002 After reviewing the supertubes and super brane-antibrane systems in the context of matrix model, we look for more general higher-dimensional configurations. For D3-bar{D3}, we find a non-trivial configuration with E cdot B not equal to 0 and descr... Yoshifumi Hyakutake, Nobuyoshi Ohta Phys.Lett. B539 (2002) 153-161 Apr 2002 We construct 1/4 BPS configurations, M-ribbons', in M-theory on T^2, which give the supertubes and supercurves in type IIA theory upon dimensional reduction. These M-ribbons are generalized so as to be consistent with the SL(2,Z) modular transfor... Masashi Hamanaka, Yasuyuki Imaizumi, Nobuyoshi Ohta Phys.Lett. B529 (2002) 163-170 Dec 2001 We study the moduli space of the D0-brane system on Dp-branes realized in the noncommutative super Yang-Mills theory. By examining the fluctuations around the solitonic solutions generated by solution generating technique, we confirm the interpret... Dongsu Bak, Nobuyoshi Ohta Phys.Lett. B527 (2002) 131-141 Dec 2001 We consider the flat supersymmetric D2 and anti-D2 system, which follows from ordinary noncommutative D2 anti-D2 branes by turning on an appropriate worldvolume electric field describing dissolved fundamental strings. We study the strings stretche... R. -G. Cai, I. Mitra, N. Ohta, S. Roy JHEP 0112:029,2001 Nov 2001 It is well-known that (, ) 5-branes of type IIB supergravity form a non-threshold bound state with (, ) strings called the (F, D1, NS5, D5) bound state where the strings lie along one of the spatial directions of the 5-branes (hep-th... Akira Fujii, Yasuyuki Imaizumi, Nobuyoshi Ohta Nucl.Phys. B615 (2001) 61-81 May 2001 It has been shown that D0-D systems can be BPS in the presence of -field even if they are not otherwise. We review the number of remaining supersymmetries, the open string ground state spectrum and the construction of the D0... Rong-Gen Cai, Yun Soo Myung, Nobuyoshi Ohta Class.Quant.Grav. 18 (2001) 5429-5440 May 2001 We obtain a Bekenstein entropy bound for the charged objects in arbitrary dimensions () using the D-bound recently proposed by Bousso. With the help of thermodynamics of CFTs corresponding to AdS Reissner-Norström (RN) black holes, we di... OM Theory and V-duality Journal of High Energy Physics 0102 024 2001 E. Bergshoeff, R-G. Cai, N. Ohta, P. K. Townsend Phys.Lett. B495 (2000) 201-206 Sep 2000 We obtain the M5-M2-MW bound state solutions of 11-dimensional supergravity corresponding to the 1/2 supersymmetric vacua of the M5-brane equations with constant background fields. In the near-horizon' case the solution interpolates between the$...
Prog.Theor.Phys. 105 (2001) 287-299      Sep 2000
We study D=3 field theories on the D3-branes stretched between two NS5-branes
with NS B-field background. The theory is a noncommutative gauge theory. The
mirror symmetry and S-duality of the theory are discussed. A new feature is
that the mirror ...
JHEP 0010 (2000) 036      Aug 2000
We show that combining the spatial noncommutative SYM limit and Lorentz
transformation, one can obtain a well-behaved light-like noncommutative SYM
limit. The light-like noncommutative SYM is unitary. When the boost velocity is
finite, the resulti...
Prog.Theor.Phys. 104 (2000) 1073-1087      Jul 2000
We discuss the properties of the bound state (F1, D1, D3) in IIB supergravity
in three different scaling limits and the transformation of the
resulting theories. In the simple decoupling limit with finite electric and
magnetic comp...

## Misc

Butsuri   60(8) 616-623   Aug 2005
According to the standard cosmology, our universe is believed to have undergone huge expansion called inflation during its early evolution after Big Bang. This behavior must be explained within general relativity and particle physics, but there is...
Prog.Theor.Phys.Suppl.148:1-28,2003      May 2002
We review the recent developments in superstrings. We start with a brief
summary of various consistent superstring theories and discuss T-duality which
necessarily leads to the presence of D-branes. The properties of D-branes are
summarized and we...
A Universal String Theory
Progress of Theoretical Physics Supplement   123 411   1996
Towards A Universal String Theory
Proceedings of the XX International colloquium on Group Theoretical Methods in Physics   377   1995
S. P. de Alwis, N. Ohta
Dec 1994
We show that the partition function for a scalar field in a static spacetime
background can be expressed as a functional integral in the corresponding
optical space, and point out that the difference between this and the
functional integral in the...

## Books etc

 handbook of Particle PhysicsOHTA Nobuyoshi (Part:Contributor, Superstring Theories)Oct 2010
 Supersymmetric TheoriesOHTA Nobuyoshi (Part:Joint Work)Nov 2006
 Encyclopedia on PhysicsOHTA Nobuyoshi (Part:Contributor, Particle Physics)Asakura   Oct 2005
 Inflation from M-TheoryUniversal Academy Press   2004

## Conference Activities & Talks

Gauge and Measure in Quantum Gravity
The 2017 Autumn Meeting of the Phyiscal Soceity   13 Sep 2017
Gauge and Parametrization dependence in Renormalization group approach to Quantum Gravity
YITP Workshop Strings and Fields 2017   Aug 2017   Yukawa Institute, Kyoto University
The 2017 Annual meeting of the Division of Gravitation and Relativistic Astrophysics of the Chinese Physical Society / The Fifth Galileo-Xu Guangqai Meeting   Jun 2017   Division of Gravitation and Relativistic Astrophysics of the Chinese Physical Society
6th CST-MISC Joint Symposium on Particle Physics   Oct 2016   Kyoto Sangyo Univ. and Nihon Univ
International Workshop for String theory and Cosmology 2016   18 Aug 2016   APCTP

## Research Grants & Projects

JSPS: Grant-in-aid
Project Year: Apr 2010 - Mar 2014    Investigator(s): KODAMA Hideo
JSPS: Grant-in-aid
Project Year: Oct 2009 - Sep 2011    Investigator(s): OHTA Nobuyoshi
Ministry of Education, Culture, Sports, Science and Technology: Grants-in-Aid for Scientific Research(基盤研究(C))
Project Year: 2008 - 2011    Investigator(s): Nobuyoshi OHTA
(抄録なし)
JSPS: International Exchange Program
Project Year: Jun 2008 - Mar 2010    Investigator(s): MAEDA Kei-Ichi
Ministry of Education, Culture, Sports, Science and Technology: Grants-in-Aid for Scientific Research(基盤研究(C))
Project Year: 2004 - 2007    Investigator(s): Nobuyoshi OHTA
We have carried out research related to quantum gravity and its consequences, which is one of the greatest problems in elementary particle physics and gravity. Since the most promising candidate for such a theory, the superstring, is defined in hi...