165 research outputs found
The Modal Logic of Stepwise Removal
We investigate the modal logic of stepwise removal of objects, both for its
intrinsic interest as a logic of quantification without replacement, and as a
pilot study to better understand the complexity jumps between dynamic epistemic
logics of model transformations and logics of freely chosen graph changes that
get registered in a growing memory. After introducing this logic
() and its corresponding removal modality, we analyze its
expressive power and prove a bisimulation characterization theorem. We then
provide a complete Hilbert-style axiomatization for the logic of stepwise
removal in a hybrid language enriched with nominals and public announcement
operators. Next, we show that model-checking for is
PSPACE-complete, while its satisfiability problem is undecidable. Lastly, we
consider an issue of fine-structure: the expressive power gained by adding the
stepwise removal modality to fragments of first-order logic
Matrix geometries and Matrix Models
We study a two parameter single trace 3-matrix model with SO(3) global
symmetry. The model has two phases, a fuzzy sphere phase and a matrix phase.
Configurations in the matrix phase are consistent with fluctuations around a
background of commuting matrices whose eigenvalues are confined to the interior
of a ball of radius R=2.0. We study the co-existence curve of the model and
find evidence that it has two distinct portions one with a discontinuous
internal energy yet critical fluctuations of the specific heat but only on the
low temperature side of the transition and the other portion has a continuous
internal energy with a discontinuous specific heat of finite jump. We study in
detail the eigenvalue distributions of different observables.Comment: 20 page
Probing the fuzzy sphere regularisation in simulations of the 3d \lambda \phi^4 model
We regularise the 3d \lambda \phi^4 model by discretising the Euclidean time
and representing the spatial part on a fuzzy sphere. The latter involves a
truncated expansion of the field in spherical harmonics. This yields a
numerically tractable formulation, which constitutes an unconventional
alternative to the lattice. In contrast to the 2d version, the radius R plays
an independent r\^{o}le. We explore the phase diagram in terms of R and the
cutoff, as well as the parameters m^2 and \lambda. Thus we identify the phases
of disorder, uniform order and non-uniform order. We compare the result to the
phase diagrams of the 3d model on a non-commutative torus, and of the 2d model
on a fuzzy sphere. Our data at strong coupling reproduce accurately the
behaviour of a matrix chain, which corresponds to the c=1-model in string
theory. This observation enables a conjecture about the thermodynamic limit.Comment: 31 pages, 15 figure
Quantum effective potential for U(1) fields on S^2_L X S^2_L
We compute the one-loop effective potential for noncommutative U(1) gauge
fields on S^2_L X S^2_L. We show the existence of a novel phase transition in
the model from the 4-dimensional space S^2_L X S^2_L to a matrix phase where
the spheres collapse under the effect of quantum fluctuations. It is also shown
that the transition to the matrix phase occurs at infinite value of the gauge
coupling constant when the mass of the two normal components of the gauge field
on S^2_L X S^2_L is sent to infinity.Comment: 13 pages. one figur
Covariant Field Equations, Gauge Fields and Conservation Laws from Yang-Mills Matrix Models
The effective geometry and the gravitational coupling of nonabelian gauge and
scalar fields on generic NC branes in Yang-Mills matrix models is determined.
Covariant field equations are derived from the basic matrix equations of
motions, known as Yang-Mills algebra. Remarkably, the equations of motion for
the Poisson structure and for the nonabelian gauge fields follow from a matrix
Noether theorem, and are therefore protected from quantum corrections. This
provides a transparent derivation and generalization of the effective action
governing the SU(n) gauge fields obtained in [1], including the would-be
topological term. In particular, the IKKT matrix model is capable of describing
4-dimensional NC space-times with a general effective metric. Metric
deformations of flat Moyal-Weyl space are briefly discussed.Comment: 31 pages. V2: minor corrections, references adde
Towards Noncommutative Fuzzy QED
We study in one-loop perturbation theory noncommutative fuzzy quenched QED_4.
We write down the effective action on fuzzy S**2 x S**2 and show the existence
of a gauge-invariant UV-IR mixing in the model in the large N planar limit. We
also give a derivation of the beta function and comment on the limit of large
mass of the normal scalar fields. We also discuss topology change in this 4
fuzzy dimensions arising from the interaction of fields (matrices) with
spacetime through its noncommutativity.Comment: 33 page
A projective Dirac operator on CP^2 within fuzzy geometry
We propose an ansatz for the commutative canonical spin_c Dirac operator on
CP^2 in a global geometric approach using the right invariant (left action-)
induced vector fields from SU(3). This ansatz is suitable for noncommutative
generalisation within the framework of fuzzy geometry. Along the way we
identify the physical spinors and construct the canonical spin_c bundle in this
formulation. The chirality operator is also given in two equivalent forms.
Finally, using representation theory we obtain the eigenspinors and calculate
the full spectrum. We use an argument from the fuzzy complex projective space
CP^2_F based on the fuzzy analogue of the unprojected spin_c bundle to show
that our commutative projected spin_c bundle has the correct
SU(3)-representation content.Comment: reduced to 27 pages, minor corrections, minor improvements, typos
correcte
Protein Kinase C Epsilon Cooperates with PTEN Loss for Prostate Tumorigenesis through the CXCL13-CXCR5 Pathway
PKCε, an oncogenic member of the PKC family, is aberrantly overexpressed in epithelial cancers. To date, little is known about functional interactions of PKCε with other genetic alterations, as well as the effectors contributing to its tumorigenic and metastatic phenotype. Here, we demonstrate that PKCε cooperates with the loss of the tumor suppressor Pten for the development of prostate cancer in a mouse model. Mechanistic analysis revealed that PKCε overexpression and Pten loss individually and synergistically upregulate the production of the chemokine CXCL13, which involves the transcriptional activation of the CXCL13 gene via the non-canonical nuclear factor κB (NF-κB) pathway. Notably, targeted disruption of CXCL13 or its receptor, CXCR5, in prostate cancer cells impaired their migratory and tumorigenic properties. In addition to providing evidence for an autonomous vicious cycle driven by PKCε, our studies identified a compelling rationale for targeting the CXCL13-CXCR5 axis for prostate cancer treatment.Centro de Investigaciones Inmunológicas Básicas y Aplicada
Matrix Models, Gauge Theory and Emergent Geometry
We present, theoretical predictions and Monte Carlo simulations, for a simple
three matrix model that exhibits an exotic phase transition. The nature of the
transition is very different if approached from the high or low temperature
side. The high temperature phase is described by three self interacting random
matrices with no background spacetime geometry. As the system cools there is a
phase transition in which a classical two-sphere condenses to form the
background geometry. The transition has an entropy jump or latent heat, yet the
specific heat diverges as the transition is approached from low temperatures.
We find no divergence or evidence of critical fluctuations when the transition
is approached from the high temperature phase. At sufficiently low temperatures
the system is described by small fluctuations, on a background classical
two-sphere, of a U(1) gauge field coupled to a massive scalar field. The
critical temperature is pushed upwards as the scalar field mass is increased.
Once the geometrical phase is well established the specific heat takes the
value 1 with the gauge and scalar fields each contributing 1/2.Comment: 41 pages,23 figures,two references added,typos corrected, extra
comments include
Numerical simulations of a non-commutative theory: the scalar model on the fuzzy sphere
We address a detailed non-perturbative numerical study of the scalar theory
on the fuzzy sphere. We use a novel algorithm which strongly reduces the
correlation problems in the matrix update process, and allows the investigation
of different regimes of the model in a precise and reliable way. We study the
modes associated to different momenta and the role they play in the ``striped
phase'', pointing out a consistent interpretation which is corroborated by our
data, and which sheds further light on the results obtained in some previous
works. Next, we test a quantitative, non-trivial theoretical prediction for
this model, which has been formulated in the literature: The existence of an
eigenvalue sector characterised by a precise probability density, and the
emergence of the phase transition associated with the opening of a gap around
the origin in the eigenvalue distribution. The theoretical predictions are
confirmed by our numerical results. Finally, we propose a possible method to
detect numerically the non-commutative anomaly predicted in a one-loop
perturbative analysis of the model, which is expected to induce a distortion of
the dispersion relation on the fuzzy sphere.Comment: 1+36 pages, 18 figures; v2: 1+55 pages, 38 figures: added the study
of the eigenvalue distribution, added figures, tables and references, typos
corrected; v3: 1+20 pages, 10 eps figures, new results, plots and references
added, technical details about the tests at small matrix size skipped,
version published in JHE
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