Searcharxiv⌕ Search

arXiv subjects

Shin Sasaki

Publications and source records attributed to Shin Sasaki.

At least 73 records · Page 4Linked to original sources
arXiv2014

BPS States in Supersymmetric Chiral Models with Higher Derivative Terms

We study the higher derivative chiral models with four supercharges and BPS states in these models. The off-shell Lagrangian generically includes higher powers of the auxiliary fields F which causes distinct on-shell branches associated with the solutions to the auxiliary fields equation. We point out that the model admits a supersymmetric completion of arbitrary higher derivative bosonic models of a single complex scalar field and an arbitrary scalar potential can be introduced even without superpotentials. As an example, we present a supersymmetric extension of the Faddeev-Skyrme model without four time derivatives, in contrast to the previously proposed supersymmetric Faddeev-Skyrme-like model containing four time derivatives. In general, higher derivative terms together with a superpotential result in deformed scalar potentials. We find that higher derivative corrections to 1/2 BPS domain walls and 1/2 BPS lumps are exactly canceled out while the 1/4 BPS lumps (as compact baby Skyrmions) depend on a characteristic feature of the higher derivative models. We also find a new 1/4 BPS condition for domain wall junctions which generically receives higher derivative corrections.

hep-th↗
arXiv2014

Non-Abelian Chern-Simons Actions in Three-dimensional Projective Superspaces

We construct an action for the superconformal Chern-Simons theory with non-Abelian gauge groups in three-dimensional N=3 projective superspace. We propose a Lagrangian given by the product of the function of the tropical multiplet, that represents the N=3 vector multiplet, and the O(-1,1) multiplet. We show how the tropical multiplet is embedded into the O(-1,1) multiplet by comparing our Lagrangian with the Chern- Simons Lagrangian in the N=2 superspace. We also discuss N=4 generalization of the action.

hep-th↗
arXiv2014

Worldsheet Description of Exotic Five-brane with Two Gauged Isometries

We study the string worldsheet description of the background geometry of the exotic $5^2_2$-brane where two isometries are gauged. This is an extension of the gauged linear sigma model (GLSM) for the exotic $5^2_2$-brane with a single gauged isometry. The new GLSM with two gauged isometries has only ${\mathcal N}=(2,2)$ supersymmetry rather than ${\mathcal N}=(4,4)$ supersymmetry of the original GLSM. This is caused by a conflict between two different $SU(2)_R$ associated with the two gauge symmetries. However, if we take a certain limit, we can find the genuine string sigma model of the background geometry of the exotic $5^2_2$-brane with ${\mathcal N}=(4,4)$ supersymmetry. We also investigate the worldsheet instanton corrections to the background geometry of the exotic $5^2_2$-brane. The worldsheet instanton corrections to the string sigma model can be traced in terms of the two gauge fields in the new GLSM. This new GLSM gives rise to a different feature of the quantum corrections from the one in the GLSM with the single gauged isometry.

hep-th↗
arXiv2014

Gauged Linear Sigma Model for Exotic Five-brane

We study an N=(4,4) supersymmetric gauged linear sigma model which gives rise to the nonlinear sigma model for multi-centered KK-monopoles. We find a new T-duality transformation of the model even in the presence of F-terms. Performing T-duality, we find the gauged linear sigma model whose IR limit describes the exotic 522-brane with B-field.

hep-th↗
arXiv2013

A Thermal Field Theory with Non-uniform Chemical Potential

We investigate thermal one-loop effective potentials in multi-flavor models with chemical potentials. We study four-dimensional models in which each flavor have different global U(1) charges. Accordingly they have different chemical potentials. We call these "non-uniform chemical potentials," which are organized into a diagonal matrix μ. The mass matrix at a vacuum does not commute with μ. We find that the effective potential is divided into three parts. The first part is the Coleman-Weinberg potential. The UV divergence resides only in this part. The second is the correction to the Coleman-Weinberg potential that is independent of temperature, and the third depends on both temperature and μ. Our result is a generalization of the thermal potentials in previous studies for models with single and multi-flavors with (uniform) chemical potentials and reproduces all the known results correctly.

hep-th↗
arXiv2013

Exploring Hot Gas at Junctions of Galaxy Filaments with Suzaku

We performed five pointing observations with Suzaku to search for hot gases associated with the junctions of galaxy filaments where no significant diffuse X-ray sources were detected so far. We discovered X-ray sources successfully in all five regions and analyzed two bright sources in each field. Spectral analysis indicates that three sources originate from X-ray diffuse halos associated with optically bright galaxies or groups of galaxies with kT~0.6-0.8 keV. Other three sources are possibly group- and cluster-scale X-ray halos with temperatures of ~1 keV and ~4 keV, respectively while the others are compact object origins such as AGNs. All the three observed intracluster media within the junctions of the galaxy filaments previously found are involved in ongoing mergers. Thus, we demonstrate that deep X-ray observations at the filament junctions identified by galaxy surveys are a powerful mean to explore growing halos in a hierarchical structure undetected so far.

astro-ph.CO↗
arXiv2013

Twisted N=4 Super Yang-Mills Theory in Omega-background

We study the twisted N=4 super Yang-Mills theories in the Omega-background with the constant R-symmetry Wilson line gauge field. Based on the classification of topological twists of N=4 supersymmetry (the half, the Vafa-Witten and the Marcus twists), we construct the deformed off-shell supersymmetry associated with the scalar supercharges for these twists. We find that the Omega-deformed action is written in the exact form with respect to the scalar supercharges as in the undeformed case.

hep-th↗
arXiv2013

Worldsheet Instanton Corrections to 522-brane Geometry

We study worldsheet instanton corrections to the exotic 522-brane geometry in type II string theory. The BPS vortices in the N=(4,4) gauged linear sigma model modify the geometry of the 522-brane. We find that the modification of the geometry is understood by the localization in the T-dualized winding direction.

hep-th↗
arXiv2013

Non-Abelian Gauge Groups and Hypermultiplets in Projective Superspaces

We construct off-shell superconformal actions of hypermultiplets coupled with non-Abelian gauge multiplets in three-dimensional N = 3 and N = 4 projective superspaces. We establish the explicit embeddings of the N = 2 vector and adjoint chiral superfields, that constitute the N = 4 gauge multiplets, into the tropical multiplets. We also construct the action in the four-dimensional N = 2 projective superspace.

hep-th↗
arXiv2013

Validity of Hydrostatic Equilibrium in Galaxy Clusters from Cosmological Hydrodynamical Simulations

We examine the validity of the hydrostatic equilibrium (HSE) assumption for galaxy clusters using one of the highest-resolution cosmological hydrodynamical simulations. We define and evaluate several effective mass terms corresponding to the Euler equations of the gas dynamics, and quantify the degree of the validity of HSE in terms of the mass estimate. We find that the mass estimated under the HSE assumption (the HSE mass) deviates from the true mass by up to ~ 30 %. This level of departure from HSE is consistent with the previous claims, but our physical interpretation is rather different. We demonstrate that the inertial term in the Euler equations makes a negligible contribution to the total mass, and the overall gravity of the cluster is balanced by the thermal gas pressure gradient and the gas acceleration term. Indeed the deviation from the HSE mass is well explained by the acceleration term at almost all radii. We also clarify the confusion of previous work due to the inappropriate application of the Jeans equations in considering the validity of HSE from the gas dynamics extracted from cosmological hydrodynamical simulations.

astro-ph.CO↗
arXiv2012

Torsion and Supersymmetry in Omega-background

We study the dimensional reduction of ten-dimensional super Yang-Mills theory in curved backgrounds with torsion. We examine the parallel spinor conditions and the constraints for the torsion parameters which preserve supersymmetry and gauge symmetry in four dimensions. In particular we examine the ten-dimensional Omega-background with the torsion which is identified with the R-symmetry Wilson line gauge fields. After the dimensional reduction, we obtain the Omega-deformed N=4 super Yang-Mills theory. Solving the parallel spinor conditions and the torsion constraints, we classify the deformed supersymmetry associated with the topological twist of N=4 supersymmetry. We also study deformed supersymmetries in the Nekrasov-Shatashvili limit.

hep-th↗
arXiv2012

Supersymmetric DBI inflation

We discuss a supersymmetric version of DBI (Dirac-Born-Infeld) inflation, which is a typical inflation model in string cosmology. The supersymmetric DBI action together with a superpotential always leads to correction terms associated with the potential into the kinetic term, which drastically change the dynamics of DBI inflation. We find two significant features of supersymmetric DBI inflation. The first one is that ultra-relativistic motion is prohibited to cause inflation, which leads to order of unity sound velocity squared and hence small non-Gaussianities of primordial curvature perturbations. The second one is that the relation between the tensor-to-scalar ratio and the field variation is modified. Then, significant tensor-to-scalar ratio $r \gtrsim 0.01$ is possible even for sub-Planck variation of the field. These new features are in sharp contrast with those of the standard non-supersymmetric DBI inflation and hence have a lot of interest implications on upcoming observations of cosmic microwave background (CMB) anisotropies by the Planck satellite as well as direct detection experiments of gravitational waves like DECIGO and BBO.

hep-th↗
arXiv2012

Sigma Model BPS Lumps on Torus

We study doubly periodic Bogomol'nyi-Prasad-Sommerfield (BPS) lumps in supersymmetric CP^{N-1} non-linear sigma models on a torus T^2. Following the philosophy of the Harrington-Shepard construction of calorons in Yang-Mills theory, we obtain the n-lump solutions on compact spaces by suitably arranging the n-lumps on R^2 at equal intervals. We examine the modular invariance of the solutions and find that there are no modular invariant solutions for n=1,2 in this construction.

hep-th↗
arXiv2012

N=4 Instanton Calculus in Omega and R-R Backgrounds

We study the instanton calculus for N=4 super Yang-Mills theory in ten-dimensional Omega-background with the R-symmetry Wilson line gauge field. From the ADHM construction of instantons in the background, we obtain the deformed instanton effective action. For a certain case we get the effective action of N=2^* theory in the Omega-background. We also study the low-energy effective D(-1)-brane action for the D3/D(-1)-brane system in the R-R 3-form field strength backgrounds and find that the action agrees with the instanton effective action in the Omega-background.

hep-th↗
arXiv2012

Deformed BPS Monopole in Omega-background

We study the BPS condition in the $Ω$-deformed $\mathcal{N}=2$ super Yang-Mills theory when one of the $ε$-parameters of the background is zero. We obtain the deformed BPS equation for dyons and the formula for their central charge. In particular, we find that the deformed BPS monopole equation has axially-symmetric solution and is equivalent to the Ernst equation. The monopole charge is shown to be undeformed. We construct one-monopole solution explicitly and examine its profile.

hep-th↗
arXiv2012

R-symmetry Breaking and O'Raifeartaigh Model with Global Symmetries at Finite Temperature

We investigate finite temperature effects in O'Raifeartaigh models with global symmetries which exhibit supersymmetry breaking at a meta-stable vacuum accompanied by $U(1)_R$ breaking. The pseudo moduli field is stabilized at one-loop order at zero temperature within some coupling parameter region. We analyze the behavior of the parameter space according to non-zero temperatures and find that the parameter region which allows $U(1)_R$ breaking is considerably extended at sufficiently low temperature, even though it shrinks down at high temperature as expected. We also discuss the thermal history of the meta-stable supersymmetry breaking vacuum.

hep-th↗
arXiv2011

BPS Monopole Equation in Omega-background

We study deformed supersymmetries in N=2 super Yang-Mills theory in the Omega-backgrounds characterized by two complex parameters $ε_1, ε_2$. When one of the $ε$-parameters vanishes, the theory has extended supersymmetries. We compute the central charge of the algebra and obtain the deformed BPS monopole equation. We examine supersymmetries preserved by the equation.

hep-th↗