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Tonguç Rador

Publications and source records attributed to Tonguç Rador.

13 recordsLinked to original sources
arXiv2017

Two-Agent Games on Graphs

We study the dynamics of evolution of points of agents placed in the vertices of a graph within the rules of two-agent units of competition where an edge is randomly chosen and the agent with higher points gets a new point with a probability $p$. The model is closely connected to generalized vertex models and anti-ferromagnetic Potts models at zero temperature. After studying the most general properties for generic graphs we confine the study to discrete d-dimensional tori. We mainly focus on the ring and torus graphs.

cond-mat.stat-mech↗
arXiv2011

Extra Dimensions, Dilaton and Dark Energy

In view of the recent observations showing that the universe is accelerating we discuss dilaton and radion stabilization from a phenomenological perspective using perfect fluid sources. One general conclusion we present is that the pressure coefficient along extra dimensions should be -2 if that of the observed dimensions is -1, the latter mimicking a cosmological constant compatible with experimental data. The conditions on the dilaton coupling are similarly strong: we find that if the coupling of the dilaton $ϕ$ to fields other than gravity is of the form $\sqrt{-g}\;e^{(a-2)ϕ}\;\mathcal{L}$ where $\mathcal{L}$ representing all other fields yielding the mentioned fluid, $a$ must be -2 if space-time dimensionality is 10. Within our approach these conditions result taking constant radion and dilaton at the level of the equations of motion. To ameliorate this we also discuss how dynamical stabilization may be achieved with a simple variant in which a dilaton potential is added in the picture where the mentioned constraints are shown to remain.

hep-th↗
arXiv2009

Chiral Vacuum Alignment and Spontaneous CP Violation by Four-Fermi Operators

In models where there is a global chiral symmetry which spontaneously breaks to its vectorial subgroup, the introduction of an explicit symmetry breaking perturbation will define the true vacuum of the theory. This true vacuum is found via the minimization of the expectation value of the perturbing hamiltonian between different vacua as prescribed by Dashen. The procedure of finding the correct vacuum of the theory may result in the spontaneous breaking of CP symmetry even if one initially demands CP invariance on the perturbation. In this work we study in detail models where the perturbation is provided by four-Fermi operators. We present exact treatment for models with two fermion flavors and study the three flavor case in depth numerically. We show that after Dashen procedure is applied the solutions for the true vacuum fall in three classes with different CP breaking patterns. Critical transitions is possible between these classes as one varies the parameters of the perturbation. We rigorously show that at these transitions a pseudo-Goldstone boson mass vanishes. We also advocate, and substantiate with numerical statistical analysis for various types of models, that if one imposes CP invariance on the perturbation before solving the vacuum alignment, the resulting vacuum structure will have a sizable probability for a light pseudo-Goldstone boson mass. That is a statistical variant of Peccei-Quinn mechanism can be speculated to operate.

hep-ph↗
arXiv2007

f(R) Gravities à la Brans-Dicke

We extend f(R) theories via the addition of a fundamental scalar field. The approach is reminiscent of the dilaton field of string theory and the Brans-Dicke model. f(R) theories attracted much attention recently in view of their potential to explain the acceleration of the universe. Extending f(R) models to theories with scalars can be motivated from the low energy effective action of string theory. There, a fundamental scalar (the dilaton), has a non-minimal coupling to the Ricci scalar. Furthermore beyond tree level actions will contain terms having higher (or lower) powers of R compared to the canonical Einstein-Hilbert term. Theories with f(R) will contain an extra scalar degree on top of the ad-hoc dilaton and mixing of these two modes around a stable solution is a concern. In this work we show that no mixing condition mandates the form $V_{1}(ϕ)f(R)+V_{2}(ϕ)R^{2}$ for the action.

hep-th↗
arXiv2007

T and S dualities and The cosmological evolution of the dilaton and the scale factors

Cosmologically stabilizing radion along with the dilaton is one of the major concerns of low energy string theory. One can hope that T and S dualities can provide a plausible answer. In this work we study the impact of S and T duality invariances on dilaton gravity. We have shown various instances where physically interesting models arise as a result of imposing the mentioned invariances. In particular S duality has a very privileged effect in that the dilaton equations partially decouple from the evolution of the scale factors. This makes it easy to understand the general rules for the stabilization of the dilaton. We also show that certain T duality invariant actions become S duality invariance compatible. That is they mimic S duality when extra dimensions stabilize.

hep-th↗
arXiv2007

Acceleration of the Universe via f(R) Gravities and The Stability of Extra Dimensions

We discuss the possibility of obtaining the present acceleration of the universe via f(R) gravity theories which recently attracted much attention. It is known that f(R) theories generally have room for this. In this work we stress that the requirement for the stabilization of extra dimensions is naturally incorporated in such a generalization of Einstein gravity under rather orthodox assumptions. We have restricted our study to pure f(R) gravity without additional matter sources partially in view of the fact that if the acceleration is to continue indefinitely any ordinary matter term is to redshift to irrelevancy and mostly for economy in understanding. The general conditions we find is that the manifold of the extra dimensional space is to have negative internal curvature and that the Ricci scalar of the full space-time manifold is also negative. The positive curvature case for extra dimensional manifold is actually the most generic case. However this necessitates a fine tuning between the Hubble constant and the size of extra dimensions in the absence of matter sources.

hep-th↗
arXiv2006

Stabilization of Extra Dimensions and The Dimensionality of the Observed Space

We present a simple model for the late time stabilization of extra dimensions. The basic idea is that brane solutions wrapped around extra dimensions, which is allowed by string theory, will resist expansion due to their winding mode. The momentum modes in principle work in the opposite way. It is this interplay that leads to dynamical stabilization. We use the idea of democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of extra dimensions, all possible winding cases are considered. To simplify the study further we assumed a symmetric decimation in which the total number of extra dimensions is taken to be $Np$ where N can be called the order of the decimation. We also assumed that extra dimensions all have the topology of tori. We show that with these rather conservative assumptions, there exists solutions to the field equations in which the extra dimensions are stabilized and that the conditions do not depend on $p$. This fact means that there exists at least one solution to the asymmetric decimation case. If we denote the number of observed space dimensions (excluding time) by $m$, the condition for stabilization is $m\geq 3$ for pure Einstein gravity and $m\leq 3$ for dilaton gravity massaged by string theory parameters.

hep-th↗
arXiv2005

Random Walk with Shrinking Steps: First Passage Characteristics

We study the mean first passage time of a one-dimensional random walker with step sizes decaying exponentially in discrete time. That is step sizes go like $λ^{n}$ with $λ\leq1$ . We also present, for pedagogical purposes, a continuum system with a diffusion constant decaying exponentially in continuous time. Qualitatively both systems are alike in their global properties. However, the discrete case shows very rich mathematical structure, depending on the value of the shrinking parameter, such as self-repetitive and fractal-like structure for the first passage characteristics. The results we present show that the most important quantitative behavior of the discrete case is that the support of the distribution function evolves in time in a rather complicated way in contrast to the time independent lattice structure of the ordinary random walker. We also show that there are critical values of $λ$ defined by the equation $λ^{K}+2λ^{P}-2=0$ with $\{K,N\}\in{\mathcal N}$ where the mean first passage time undergo transitions.

cond-mat.stat-mech↗
arXiv2005

Vibrating Winding Branes, Wrapping Democracy and Stabilization of Extra Dimensions in Dilaton Gravity

We show that, in the context of dilaton gravity, a recently proposed democratic principle for intersection possibilities of branes winding around extra dimensions yield stabilization, even with the inclusion of momentum modes of the wrapped branes on top of the winding modes. The constraints for stabilization massaged by string theory inputs forces the number of observed dimensions to be three. We also discuss consequences of adding ordinary matter living in the observed dimensions.

hep-th↗
arXiv2005

Intersection Democracy for Winding Branes and Stabilization of Extra Dimensions

We show that, in the context of pure Einstein gravity, a democratic principle for intersection possibilities of branes winding around extra dimensions in a given partitioning yield stabilization, while what the observed space follows is matter-like dust evolution . Here democracy is used in the sense that, in a given decimation of extra dimensions, all possible wrappings and hence all possible intersections are allowed. Generally, the necessary and sufficient condition for this is that the dimensionality $m$ of the observed space dimensions obey $3\leqm \le N$ where $N$ is the decimation order of the extra dimensions.

hep-th↗
arXiv2003

Flavor Democracy: On which basis?

I argue that flavor democracy should not be considered as a "mere" assumption, but rather a fact that is inherent where there is hierarchy of quark masses. Briefly the crux of the argument is the ambiguity of defining a basis when one introduces a mass matrix. That is there is a degree of freedom of also defining a basis other than the weak eigenbasis with respect to which one can write down mass matrices. Since the ultimate aim is to diagonalize to the mass eigenbasis this is physically equivalent. But not necessarily so for the human eye.

hep-ph↗
arXiv2002

Inflation via Black Holes with Quantized Area Spectrum

I present a very simplistic toy model for the inflationary paradigm where the size of the universe undergoes a period of exponential growth. The basic assumption I make use of is that black holes might have a quantized area (mass) spectrum with a stable ground state and that the universe has started with a tightly packed collection of these objects alone.

hep-th↗