159 research outputs found
RG flows from Spin(7), CY 4-fold and HK manifolds to AdS, Penrose limits and pp waves
We obtain explicit realizations of holographic renormalization group (RG)
flows from M-theory, from E^{2,1} \times Spin(7) at UV to AdS_4 \times
\tilde{S^7} (squashed S^7) at IR, from E^{2,1} \times CY4 at UV to AdS_4 \times
Q^{1,1,1} at IR, and from E^{2,1} \times HK (hyperKahler) at UV to AdS_4 \times
N^{0,1,0} at IR. The dual type IIA string theory configurations correspond to
D2-D6 brane systems where D6 branes wrap supersymmetric four-cycles. We also
study the Penrose limits and obtain the pp-wave backgrounds for the above
configurations. Besides, we study some examples of non-supersymmetric and
supersymmetric flows in five-dimensional gauge theories.Comment: 42 pages, 6 eps figures, typos and misprints correcte
A Massive Renormalizable Abelian Gauge Theory in 2+1 Dimensions
The standard formulation of a massive Abelian vector field in
dimensions involves a Maxwell kinetic term plus a Chern-Simons mass term; in
its place we consider a Chern-Simons kinetic term plus a Stuekelberg mass term.
In this latter model, we still have a massive vector field, but now the
interaction with a charged spinor field is renormalizable (as opposed to super
renormalizable). By choosing an appropriate gauge fixing term, the Stuekelberg
auxiliary scalar field decouples from the vector field. The one-loop spinor
self energy is computed using operator regularization, a technique which
respects the three dimensional character of the antisymmetric tensor
. This method is used to evaluate the vector self
energy to two-loop order; it is found to vanish showing that the beta function
is zero to two-loop order. The canonical structure of the model is examined
using the Dirac constraint formalism.Comment: LaTeX, 17 pages, expanded reference list and discussion of
relationship to previous wor
D-branes on AdS flux compactifications
We study D-branes in N=1 flux compactifications to AdS_4. We derive their
supersymmetry conditions and express them in terms of background generalized
calibrations. Basically because AdS has a boundary, the analysis of stability
is more subtle and qualitatively different from the usual case of Minkowski
compactifications. For instance, stable D-branes filling AdS_4 may wrap trivial
internal cycles. Our analysis gives a geometric realization of the
four-dimensional field theory approach of Freedman and collaborators.
Furthermore, the one-to-one correspondence between the supersymmetry conditions
of the background and the existence of generalized calibrations for D-branes is
clarified and extended to any supersymmetric flux background that admits a
time-like Killing vector and for which all fields are time-independent with
respect to the associated time. As explicit examples, we discuss supersymmetric
D-branes on IIA nearly Kaehler AdS_4 flux compactifications.Comment: 43 pages, 2 pictures, 1 table; v2: added references, color to figure
and corrected typo in (6.21b
Jack superpolynomials with negative fractional parameter: clustering properties and super-Virasoro ideals
The Jack polynomials P_\lambda^{(\alpha)} at \alpha=-(k+1)/(r-1) indexed by
certain (k,r,N)-admissible partitions are known to span an ideal I^{(k,r)}_N of
the space of symmetric functions in N variables. The ideal I^{(k,r)}_N is
invariant under the action of certain differential operators which include half
the Virasoro algebra. Moreover, the Jack polynomials in I^{(k,r)}_N admit
clusters of size at most k: they vanish when k+1 of their variables are
identified, and they do not vanish when only k of them are identified. We
generalize most of these properties to superspace using orthogonal
eigenfunctions of the supersymmetric extension of the trigonometric
Calogero-Moser-Sutherland model known as Jack superpolynomials. In particular,
we show that the Jack superpolynomials P_{\Lambda}^{(\alpha)} at
\alpha=-(k+1)/(r-1) indexed by certain (k,r,N)-admissible superpartitions span
an ideal {\mathcal I}^{(k,r)}_N of the space of symmetric polynomials in N
commuting variables and N anticommuting variables. We prove that the ideal
{\mathcal I}^{(k,r)}_N is stable with respect to the action of the
negative-half of the super-Virasoro algebra. In addition, we show that the Jack
superpolynomials in {\mathcal I}^{(k,r)}_N vanish when k+1 of their commuting
variables are equal, and conjecture that they do not vanish when only k of them
are identified. This allows us to conclude that the standard Jack polynomials
with prescribed symmetry should satisfy similar clustering properties. Finally,
we conjecture that the elements of {\mathcal I}^{(k,2)}_N provide a basis for
the subspace of symmetric superpolynomials in N variables that vanish when k+1
commuting variables are set equal to each other.Comment: 36 pages; the main changes in v2 are : 1) in the introduction, we
present exceptions to an often made statement concerning the clustering
property of the ordinary Jack polynomials for (k,r,N)-admissible partitions
(see Footnote 2); 2) Conjecture 14 is substantiated with the extensive
computational evidence presented in the new appendix C; 3) the various tests
supporting Conjecture 16 are reporte
Graft immaturity and safety concerns in transplanted human kidney organoids
For chronic kidney disease, regeneration of lost nephrons with human kidney organoids derived from induced pluripotent stem (iPS) cells is proposed to be an attractive potential therapeutic option. It remains unclear, however, whether organoids transplanted into kidneys in vivo would be safe or functional. Here, we purified kidney organoids and transplanted them beneath the kidney capsules of immunodeficient mice to test their safety and maturity. Kidney organoid grafts survived for months after transplantation and became vascularized from host mouse endothelial cells. Nephron-like structures in grafts appeared more mature than kidney organoids in vitro, but remained immature compared with the neighboring mouse kidney tissue. Ultrastructural analysis revealed filtration barrier-like structures, capillary lumens, and tubules with brush border in the transplanted kidney organoids, which were more mature than those of the kidney organoids in vitro but not as organized as adult mammalian kidneys. Immaturity was a common feature of three separate differentiation protocols by immunofluorescence analysis and single cell RNA sequencing. Stroma of transplanted kidney organoid grafts were filled with vimentin-positive mesenchymal cells, and chondrogenesis, cystogenesis, and stromal expansion were observed in the long term. Transcription profiles showed that long-term maintenance after kidney organoid transplantation induced transcriptomic reprogramming with prominent suppression of cell-cycle-related genes and upregulation of extracellular matrix organization. Our data suggest that kidney organoids derived from iPS cells may be transplantable but strategies to improve nephron differentiation and purity are required before they can be applied in humans as a therapeutic option.11Ysciescopuskc
Comments on D-brane Interactions in PP-wave Backgrounds
We calculate the interaction potential between widely separated D-branes in
PP-wave backgrounds in string theory as well as in low-energy supergravity.
Timelike and spacelike orientations are qualitatively different but in both
cases the effective brane tensions and RR charges take the same values as in
Minkowski space in accordance with the expectations from the sigma model
perturbation theory.Comment: Latex, 22 pages. Typos corrected and a reference added, final versio
Holographic Uniformization
We derive and study supergravity BPS flow equations for M5 or D3 branes
wrapping a Riemann surface. They take the form of novel geometric flows
intrinsically defined on the surface. Their dual field-theoretic interpretation
suggests the existence of solutions interpolating between an arbitrary metric
in the UV and the constant-curvature metric in the IR. We confirm this
conjecture with a rigorous global existence proof.Comment: 52 pages, 3 figure
Superstrings with Intrinsic Torsion
We systematically analyse the necessary and sufficient conditions for the
preservation of supersymmetry for bosonic geometries of the form R^{1,9-d}
\times M_d, in the common NS-NS sector of type II string theory and also type
I/heterotic string theory. The results are phrased in terms of the intrinsic
torsion of G-structures and provide a comprehensive classification of static
supersymmetric backgrounds in these theories. Generalised calibrations
naturally appear since the geometries always admit NS or type I/heterotic
fivebranes wrapping calibrated cycles. Some new solutions are presented. In
particular we find d=6 examples with a fibred structure which preserve N=1,2,3
supersymmetry in type II and include compact type I/heterotic geometries.Comment: 58 pages, LaTeX; v2: New section on solutions including an example
with N=3 supersymmetry and discussion of heterotic compactifications. Details
on conventions and references added. v3: added an explicit example of
non-integrable product structure in Appendix C; some typos fixe
D3/D7 Inflationary Model and M-theory
A proposal is made for a cosmological D3/D7 model with a constant magnetic
flux along the D7 world-volume. It describes an N=2 gauge model with
Fayet-Iliopoulos terms and the potential of the hybrid P-term inflation. The
motion of the D3-brane towards D7 in a phase with spontaneously broken
supersymmetry provides a period of slow-roll inflation in the de Sitter valley,
the role of the inflaton being played by the distance between D3 and D7-branes.
After tachyon condensation a supersymmetric ground state is formed: a D3/D7
bound state corresponding to an Abelian non-linear (non-commutative) instanton.
In this model the existence of a non-vanishing cosmological constant is
associated with the resolution of the instanton singularity. We discuss a
possible embedding of this model into a compactified M-theory setup.Comment: 30 pages, 4 figures, LaTeX; v2, minor typos corrected, one reference
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Cosmological evolution of interacting dark energy in Lorentz violation
The cosmological evolution of an interacting scalar field model in which the
scalar field interacts with dark matter, radiation, and baryon via Lorentz
violation is investigated. We propose a model of interaction through the
effective coupling . Using dynamical system analysis, we study the
linear dynamics of an interacting model and show that the dynamics of critical
points are completely controlled by two parameters. Some results can be
mentioned as follows. Firstly, the sequence of radiation, the dark matter, and
the scalar field dark energy exist and baryons are sub dominant. Secondly, the
model also allows the possibility of having a universe in the phantom phase
with constant potential. Thirdly, the effective gravitational constant varies
with respect to time through . In particular, we consider a simple
case where has a quadratic form and has a good agreement with the
modified CDM and quintessence models. Finally, we also calculate the
first post--Newtonian parameters for our model.Comment: 14 pages, published versio
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