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...

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...

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...

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...

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 ...

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
radiation, we...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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.

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...

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...

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...

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...

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...

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 ...

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...

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 ...

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
asymptotically AdS with a no...

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...

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...

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...

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...

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...

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 ...

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...

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...

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...

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...

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...

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...

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...

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 ...

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...

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...

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...

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...

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...

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,...

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...

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...

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 ...

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...

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...

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, ...

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...

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...

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...

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 ...

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...

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 ...

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...

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...

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...

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 ...

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...

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...

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...

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...

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...

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...

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...

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 $...

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 ...

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...

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...

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...

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

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...

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

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...