Brane Potential Research Articles

Note on warped compactification. Finite brane potentials and non-Hermiticity

We study radius stabilization in the Randall-Sundrum model without assuming any unnaturally large stabilizing scalar potential parameter at the boundary branes (γ) by the frequently used superpotential method. Employing a perturbative expansion in 1/γ2 and the backreaction parameter, we obtain approximate analytical expressions for the radion mass and wavefunction. We validate them through a dedicated numerical analysis, which solves the linearized coupled scalar and metric field equations exactly. It is observed that the radion mass decreases with decreasing γ. Below a critical value of γ, the radion becomes tachyonic, suggesting destabilization of the extra dimension. We also address the issue of non-Hermiticity of the differential operator that determines the radion and Kaluza-Klein (KK) mode wavefunctions in the finite γ limit. It is accomplished by finding an explicit form of the general scalar product that re-establishes the orthogonality in the KK decomposition.

The Role of Mitochondria in the Development of Nervous System Diseases and Mental Disorders

The review analyzed articles from the Pub- Med database mainly from the last 10 years, indicating the role of mitochondria in the development of diseases of the central nervous system and mental disorders. Mu- tations in mitochondrial/nuclear DNA genes, oxidative stress, impaired redox mechanisms, and regulation of mitochondrial dynamics have been found to cause mito- chondrial dysfunction. At the same time, the permeabil- ity of mitochondrial membranes changes, the influx of calcium ions increases, as a result of which the mem- brane potential shifts, oxidation processes become more intense, a large number of reactive oxygen species are formed, oxidative phosphorylation is disrupted, and the process of neuronal apoptosis starts. Mitochondrial dys- function is a common pathogenetic mechanism of Alz- heimer's and Parkinson's diseases, amyotrophic lateral sclerosis, Huntington's chorea, epilepsy, schizophrenia, etc. Discoveries and advances in molecular genetics have increased our understanding of the early pathology of mitochondrial disorders, enabled disease modeling, and provided entirely new perspectives on molecular pathogenesis. It is necessary that this research continues and then, in the near future, it will help develop the search for possible ways to treat the diseases that people suffer from.

Holographic duals of the mathcal{N} = 1* gauge theory

We use the long-wavelength effective theory of black branes (blackfold approach) to perturbatively construct holographic duals of the vacua of the mathcal{N} = 1* supersymmetric gauge theory. Employing the mechanism of Polchinski and Strassler, we consider wrapped black five-brane probes with D3-brane charge moving in the perturbative supergravity back-grounds corresponding to the high- and low-temperature phases of the gauge theory. Our approach recovers the results for the brane potentials and equilibrium configurations known in the literature in the extremal limit, while away from extremality we find metastable black D3-NS5 configurations with horizon topology ℝ3 × \U0001d54a2 × \U0001d54a3 in certain regimes of parameter space, which cloak potential brane singularities. We uncover novel features of the phase diagram of the mathcal{N} = 1* gauge theory in different ensembles and provide further evidence for the appearance of metastable states in holographic backgrounds dual to confining gauge theories.

Gupta–Feynman-based quantum theory of gravity and the compressed space

In this work, we develop the quantum theory of gravity in the gravitational compressed space. The equivalence of spatial compression to the Lorentz contraction of special relativity, supported by the relative gravitational red-shift using the black hole clock, leads to the brane potential and gives the minimum length at which the extra dimensions become dominant, comparable to that of the Schwarzschild radius. For Planck mass the minimum length is almost Planck’s length. When doing the quantization of the theory, we find that those responsible for the evolution of time for luminous matter, graviton and for dark matter, the axion, have the property that in compressed gravitational space, naked and dressed propagators are equal and coincide with the corresponding naked propagators.

The Continuum Linear Dilaton

Continuum spectra can be a way out to alleviate the tension generated by the elusiveness of narrow resonances of new physics in direct experimental searches. Motivated by the latter, we consider the linear dilaton model with a continuum spectrum of KK modes. It is provided by a critical exponential bulk potential for the scalar field stabilizing the distance, between the UV boundary at $y=0$ and a naked (good) singularity at $y=y_s$, in proper coordinates, which corresponds in conformal coordinates to $z_s\to\infty$. The cutoff $M_s$ in this theory is an intermediate scale $M_s\simeq 10^{-5}M_{\rm Pl}$ and the warped factor solves the hierarchy between $M_s$ and the TeV, while the hierarchy between $M_{\rm Pl}$ and $M_s$ has to be solved by a (Little) String Theory with coupling $g_s\simeq 10^{-5}$. The Standard Model is localized on a 4D IR brane. The graviton and radion Green's and spectral functions have a continuum of states with a TeV mass gap, and isolated poles consisting on the 4D graviton and the light radion/dilaton. We construct the effective field theory below the mass gap where the continua of KK modes are integrated out, generating a set of dimension eight operators which contribute to low energy electroweak precision observables, and high energy violation of unitarity in vector boson scattering processes. The radion mass depends on the stabilizing UV brane potential and its wave function is localized toward the IR which enhances its coupling with the SM fields.

Ziziphora clinopodioides flavonoids based on network pharmacology attenuates atherosclerosis in rats induced by high-fat emulsion combined with vitamin D3 by down-regulating VEGF/AKT/NF-κB signaling pathway

Ziziphora clinopodioides flavonoids (ZCF) is a major bioactive total flavonoids compound isolated from Ziziphora clinopodioides Lam. It has been long used as an anti-atherosclerosis (AS) in clinics. However, anti-AS effects of ZCF have not been fully investigated. The objective of this study is to further investigate the anti-AS activities and mechanisms of ZCF in vivo. The main chemical components, action targets and signal pathways of Ziziphora clinopodioides Lam were predicted and analyzed by network pharmacology technology. The main bioactive components of Ziziphora clinopodioides Lam were identified using high performance liquid chromatography-mass spectrometry (HPLC-MS). In vivo experiments, atherosclerosis in rats induced by high-fat emulsion combined with vitamin D3 and treated with simvastatin (0.45 mg/kg/d), ZCF (6.25, 12.5, 25 g/kg/d) for 7 weeks.We found that ZCF significantly reduced blood lipid levels (TG, TC, and LDL-C), and decreased lipid deposition in the aorta and atherosclerotic lesion size, inhibited mitochondrial mem- brane potential (MMP2/9/12/13) impairment. Meanwhile, ZCF may down-regulated the levels of VEGF, AKT, NF-κB, ICAM-1 and VCAM-1 proteins, indicating ZCF may play an anti-atherosclerotic role by down-regulating the VEGF/AKT/NF-κB signaling pathway.Results from this study demonstrated that ZCF have an anti-AS ability to lower lipid concentrations and protect endothelial function, antioxidant and anti-inflammatory activity, and suggested that ZCF might be a potential therapeutic drug in the prevention of AS.

Gapped continuum Kaluza-Klein spectrum

We consider a warped five-dimensional model with an ultraviolet (UV) brane and, on top of the Standard Model isolated modes, continua of KK modes with different mass gaps for all particles: gauge bosons, fermions, graviton, radion and Higgs boson. The model can be considered as a modelization in five dimensions of gapped unparticles. The five dimensional metric has a singularity, at a finite (infinite) value of the proper (conformal) coordinate, which is admissible as it supports finite temperature in the form of a black hole horizon. An infrared (IR) brane, with particular jumping conditions, is introduced to trigger correct electroweak breaking. The gravitational metric is AdS5 near the UV brane, to solve the hierarchy problem with a fundamental Planck scale, and linear, in conformal coordinates, near the IR, as in the linear dilaton and five-dimensional clockwork models. The branes, and singularity, distances are fixed, à la Goldberger-Wise, by a bulk scalar field with brane potentials explicitly breaking the conformal symmetry. The bosonic continuum of KK modes with the smallest mass gap are those of gauge bosons, and so they are the most likely produced at the LHC. Mass gaps of the continuum of KK fermions do depend on their localization in the extra dimension. We have computed the spectral functions, and arbitrary Green’s functions, and shown how they can modify some Standard Model processes.

Phase structures of the black Dp-D(p + 4)-brane system in various ensembles II: electrical and thermodynamic stability

By incorporating the electrical stability condition into the discussion, we continue the study on the thermodynamic phase structures of the Dp-D(p + 4) black brane in GG, GC, CG, CC ensembles defined in our previous paper [27]. We find that including the electrical stability conditions in addition to the thermal stability conditions does not modify the phase structure of the GG ensemble but puts more constraints on the parameter space where black branes can stably exist in GC, CG, CC ensembles. In particular, the van der Waals-like phase structure which was supposed to be present in these ensembles when only thermal stability condition is considered would no longer be visible, since the phase of the small black brane is unstable under electrical fluctuations. However, the symmetry of the phase structure by interchanging the two kinds of brane charges and potentials is still preserved, which is argued to be the result of T-duality.

SPINFLATION WITH BACKREACTION

We study brane inflation in flux compactifications at the nonlinear level, solving the D3-brane DBI-equations of motion including backreaction from the D3–D7 brane potential and from perturbations of the warp factor. We first numerically compute the exact functional form of the Kähler modulus valid on the entire supergravity background and obtain a two-field potential along radial and harmonic directions. We find that a valid perturbative expansion on the entire supergravity background with the Kähler modulus integrated out adiabatically in DBI inflation requires hierarchies of scales that determine compactification parameters different from those typical in slow-roll models. Our numerical results then show that the DBI inflationary solutions are quite robust against these nonlinear corrections.

Slow-walking inflation

We propose a new model of slow-roll inflation in string cosmology, based on warped throat supergravity solutions displaying 'walking' dynamics, i.e. the coupling constant of the dual gauge theory slowly varies over a range of energy scales. The features of the throat geometry are sourced by a rich field content, given by the dilaton and RR and NS fluxes. By considering the motion of a D3-brane probe in this geometry, we are able to analytically calculate the brane potential in a physically interesting regime. This potential has an inflection point: in its proximity we realize a model of inflation lasting sixty e-foldings, and whose robust predictions are in agreement with current observations. We are also able to interpret some of the most interesting aspects of this scenario in terms of the properties of the QFT dual theory.

Warped radion inflation

We show that the radion in a warped geometry bounded by two branes can have a potential suitable for inflation. Our construction is based upon a solution known in string theory as the linear dilaton, in which the back-reaction from a bulk scalar \Phi is exactly accounted for. The radion, stabilized by \Phi, is much heavier than the TeV scale and its couplings to the standard model are much more suppressed than in the usual Randall-Sundrum solution. We present a new formalism for obtaining approximate time-dependent solutions, based on perturbing the exact solution to the coupled Einstein and scalar field equations in the bulk. It allows the radion potential to be computed directly in terms of the brane potentials for \Phi. We show that simple exponential potentials on the branes can lead to a 4D radion potential with a flattened hilltop form, yielding inflation with a spectral index of typically n_s=0.96 and no higher than 0.99. With more complicated brane potentials, the descent from the hilltop can be a linear potential, giving a tensor-to-scalar ratio as large as r=0.07 with n_s=0.974. The couplings of the radion to the standard model particles are dictated by general covariance, so the details of reheating are explicitly calculable, leading to a reheat temperature of at least 10^7 GeV. The quantum corrections to the inflaton potential from its couplings to matter are also calculable and are shown to be small, so that the prediction for the shape of the potential is under theoretical control, even with superPlanckian field excursions.

Static brane solutions stabilized by nonlinear bulk scalar dynamics

We study a nonlinear sigma-model-like theory of a bulk scalar field coupled to the five-dimensional Einstein gravity with a negative cosmological constant. We determine the structure of the non-factorizable spacetime which our Minkowskian brane bounds, when the pressure in the extra dimension is proportional to the energy density of the scalar field as with a constant ω5. With these static solutions clarified by the parameter ω5, we fix the size of the extra dimension in terms of the bulk and brane potentials of the scalar field, imposing the stability condition in the cases of the 2-branes. The hierarchy problem is discussed in their Randall–Sundrum-like limit, and one of the static solutions obtained in the case of a strong bulk potential ω5 < 0 is interpreted as a thick 1-brane model.

Five dimensional cosmology in Horava-Witten M theory

The cosmology in the Hubble expansion era of the Horava-Witten M theory compactified on a Calabi-Yau threefold is studied in the reduction to five-dimensions where the effects of the Calabi-Yau manifold are summarized by the volume modulus, and all perturbative potentials are included. Matter on the branes are treated as first order perturbations of the static vacuum solution, and all equations in the bulk and all boundary conditions on both end branes are imposed. It is found that for a static volume modulus and a static fifth dimension, $y$, one can recover the four-dimensional Robertson Friedmann Walker cosmology for relativistic matter on the branes, but not for nonrelativistic matter. In this case, the Hubble parameter $H$ becomes independent of $y$ to first order in matter density. This result holds also when an arbitrary number of 5-branes are included in the bulk. The five-dimensional Horava-Witten model is compared with the Randall-Sundrum phenomenology with a scalar field in the bulk where a bulk and brane potential are used so that the vacuum solutions can be rigorously obtained. (In the Appendix, the difficulty of obtaining approximate vacuum solutions for other potentials is discussed.) In this case nonrelativistic matter is accommodated by allowing the distance between the branes to vary. It is suggested that nonperturbative potentials for the vacuum solution of Horava-Witten theory are needed to remove the inconsistency that nonrelativistic matter creates.

Second order perturbations in the radius stabilized Randall-Sundrum two branes model. II. Effect of relaxing strong coupling approximation

We discuss gravitational perturbations in the Randall-Sundrum two branes model with radius stabilization. Following the idea by Goldberger and Wise for the radius stabilization, we introduce a scalar field which has potentials localized on the branes in addition to a bulk potential. In our previous paper we discussed gravitational perturbations induced by static, spherically symmetric and nonrelativistic matter distribution on the branes under the condition that the values of the scalar field on the respective branes cannot fluctuate due to its extremely narrow brane potentials. We call this case the strong coupling limit. Our concern in this paper is to generalize our previous analysis relaxing the limitation of taking the strong coupling limit. We find that new corrections in metric perturbations due to relaxing the strong coupling limit enhance the deviation from the 4D Einstein gravity only in some exceptional cases. In the case that matter fields reside on the negative tension brane, the stabilized radion mass becomes very small when the new correction becomes large.

Warped geometry of brane worlds

We study the dynamical equations for extra-dimensional dependence of a warp factor and a bulk scalar in 5D brane world scenarios with induced brane metric of constant curvature. These equations are similar to those for the time dependence of the scale factor and a scalar field in 4D cosmology, but with the sign of the scalar field potential reversed. Based on this analogy, we introduce novel methods for studying the warped geometry. We construct the full phase portraits of the warp factor/scalar system for several examples of the bulk potential. This allows us to view the global properties of the warped geometry. For flat branes, the phase portrait is two dimensional. Moving along typical phase trajectories, the warp factor is initially increasing and finally decreasing. All trajectories have timelike gradient-dominated singularities at one or both of their ends, which are reachable in a finite distance and must be screened by the branes. For curved branes, the phase portrait is three dimensional. However, as the warp factor increases the phase trajectories tend towards the two-dimensional surface corresponding to flat branes. We discuss this property as a mechanism that may stretch the curved brane to be almost flat, with a small cosmological constant. Finally, we describe the embedding of branes in the 5D bulk using the phase space geometric methods developed here. In this language the boundary conditions at the branes can be described as a 1D curve in the phase space. We discuss the naturalness of tuning the brane potential to stabilize the brane world system.

Pyrotechnic universe

One of the central points of the ekpyrotic cosmological scenario based on Horava-Witten theory is that we live on a negative tension brane. However, the tension of the visible brane is positive in the usual HW phenomenology with stronger coupling on the hidden brane, both for standard and non-standard embedding. To make ekpyrotic scenario realistic one must solve the problem of the negative cosmological constant on the visible brane and fine-tune the bulk brane potential with an accuracy of $10^{-50}$. In terms of a canonically normalized scalar field $\phi$ describing the position of the brane, this potential must take a very unusual form $V(\phi)\sim e^{-{5000 \phi\over M_p}}$. We describe the problems which appear when one attempts to obtain this potential in string theory. The mechanism for the generation of density perturbations in this scenario is not brane-specific; it is a particular limiting case of the mechanism of tachyonic preheating. Unlike inflation, this mechanism exponentially amplifies not only quantum fluctuations, but also initial inhomogeneities. As a result, to solve the homogeneity problem in this scenario, one would need the branes to be parallel to each other with an accuracy better than $10^{-60}$ on a scale $10^{30}$ times greater than the distance between the branes. Thus, at present, inflation remains the only robust mechanism that produces density perturbations with a flat spectrum and simultaneously solves all major cosmological problems.

Brane-world cosmology of modulus stabilization with a bulk scalar field

We point out that the potential of Goldberger and Wise for stabilizing the distance between two 3-branes, separated from each other along an extra dimension with a warp factor, has a metastable minimum when the branes are infinitely separated. The classical evolution of the radion (brane separation) will place it in this false minimum for generic initial conditions. In particular, inflation could do this if the expansion rate is sufficiently large. We present a simplified version of the Goldberger-Wise mechanism in which the radion potential can be computed exactly, and we calculate the rate of thermal transitions to the true minimum, showing that model parameters can be chosen to ensure that the universe reaches the desired final state. Finiteness of bulk scalar field brane potentials can have an important impact on the nucleation rate, and it can also significantly increase the predicted mass of the radion.

Brane world scenario with m-form field: stabilisation of radion modulus and self-tuning solutions

We consider ( n+ m+1)-dimensional bulk spacetime, containing flat ( n+ m−1)-dimensional parallel branes, with topology R n−1× T m . We assume that the graviton and an m-form field are the only bulk fields and that the m-form field has nonvanishing components along the T m directions only. We then find that the m-form field, with suitable bulk and brane potentials, can stabilise the radion modulus at the required value with no fine tuning. We find self-tuning solutions also.

Periodic Current Injection (PCI) -A New Method to Image Steady-State Membrane Potential of Single Neurons in situ Using Extracellular Voltage-Sensitive Dyes

A new method is described which allows to image the steady-state distribution of membrane potential of single neurons in situ. The method consists of staining the tissue with an extracellular voltage-sensitive dye (Di-4-ANEPPS) and impaling a single neuron with a microelectrode. After focusing the imaging system onto the cell a large series of images are taken with a CCD camera at the appropriate excitation wavelength of the voltage-sensitive dye while the neuron's membrane potential is shifted by a periodic current injection (PCI). Afterwards two groups of images are averaged separately: those images while the cell was at rest and those images while the cell was hyperpolarized. After subtraction of these averaged images, the resulting difference image shows only the membrane potential of the cell which was altered periodically. The success of the method is demonstrated on leech cells in intact ganglia. If applied to cells with a basically two-dimensional arborization pattern, the decrease of activity in the difference image in areas further away from the injection site should relate to a decrease in membrane potential according to the passive electrotonic properties of the cell under study.

Structural elements involved in specific K+ channel functions.

K+ channels represent a diverse group of ion channels that have been found in most eukaryotic cells of the animal and plant kingdom. The functions of these channels, such as the regulation of neuronal excitability and hormone release, and movements of the stomatal pores in plants (12, 17, 36, 38, 42a, 75, 87), depend on the specific manner in which a particular K+ channel opens and closes, and its selective penneation by K+ ions. A wide range of these channel properties has been observed, which are probably crucial for subserv­ ing different physiological functions. For example, some K+ channels are activated or modulated by second messengers such as Ca2+, A TP, inositol triphosphate, and G proteins, while others are activated by changes in mem­ brane potential (11, 18, 51, 64, 81, 84, 96). Whereas some K+ channels, such as the inward rectifiers, are voltage-dependent because their pores are blocked in a voltage-dependent manner by certain cations (e.g. Mg2+) (61, 62), other channels appear to be intrinsically sensitive to voltage so that changes of membrane potential induce conformational changes in these chan­ nels that lead to channel opening (36). These voltage-gated K+ channels differ in the range over which changes in membrane potential produce channel activation and in the rates of transitions between the open (conducting) and various non-conducting states of the channel (36, 81, 84).