By implementing an error function on a Machine Learning algorithm we look for minimal conditions to construct stable Anti de Sitter and de Sitter vacua from dimensional type IIB String theory ...compactification on Kähler manifolds with torsion. This allows to have contributions to the scalar potential from the five-form flux and from D-branes wrapping torsional cycles, interpreted as non-BPS states. The former implies the possibility to construct stable AdS vacua while the latter constitutes a mechanism to uplift AdS to dS vacua. Particularly we consider
D
5
^
non-BPS states to uplift the stable AdS vacua to an (apparently) stable dS minimum. Both results – the generation of an AdS vacuum and the corresponding uplifting to a dS one – are restricted to a certain type of configurations, specifically with the number of
O
3 orientifolds bounded from below by the number of
D
3-branes and fluxes. Under these conditions, we report over 170 dS (classical) stable vacua. In all of them, the uplifted effective potential becomes very flat indicating the presence of possible sources of instabilities. We comment on their relationship with the Swampland Conjectures.
Testing swampland conjectures with machine learning Bizet, Nana Cabo; Damian, Cesar; Loaiza-Brito, Oscar ...
The European physical journal. C, Particles and fields,
08/2020, Letnik:
80, Številka:
8
Journal Article
Recenzirano
Odprti dostop
We consider Type IIB compactifications on an isotropic torus
T
6
threaded by geometric and non geometric fluxes. For this particular setup we apply supervised machine learning techniques, namely an ...artificial neural network coupled to a genetic algorithm, in order to obtain more than sixty thousand flux configurations yielding to a scalar potential with at least one critical point. We observe that both stable AdS vacua with large moduli masses and small vacuum energy as well as unstable dS vacua with small tachyonic mass and large energy are absent, in accordance to the refined de Sitter conjecture. Moreover, by considering a hierarchy among fluxes, we observe that perturbative solutions with small values for the vacuum energy and moduli masses are favored, as well as scenarios in which the lightest modulus mass is much smaller than the corresponding AdS vacuum scale. Finally we apply some results on random matrix theory to conclude that the most probable mass spectrum derived from this string setup is that satisfying the Refined de Sitter and AdS scale conjectures.
Based on the flux‐scaling scenario we study a model consisting on Type IIB string theory compactified on a Calabi‐Yau manifold with a frozen complex structure in the presence of generic fluxes. The ...model contains (meta)stable Minkowski and de Sitter vacua as well as inflationary directions driven by two independent linear combination of axions. Due to a numerical control by fluxes, we show that cosmological parameters as the spectral index, tensor‐to‐scalar ratio and non‐Gaussianities can be kept within observed bounds while preserving the desired hierarchies on physical scales. Moreover we compute the deviation of the inflationary trajectories from geodesics on field space in terms of the fluxes showing that for some regions, they fulfill the recent proposed swampland criterion for multi‐field scenarios.
Based on the flux‐scaling scenario a model is studied consisting on Type IIB string theory compactified on a Calabi‐Yau manifold with a frozen complex structure in the presence of generic fluxes. The model contains (meta)stable Minkowski and de Sitter vacua as well as inflationary directions driven by two independent linear combination of axions. Due to a numerical control by fluxes, the authors show that cosmological parameters as the spectral index, tensor‐to‐scalar ratio and non‐Gaussianities can be kept within observed bounds while preserving the desired hierarchies on physical scales. Moreover The deviation of the inflationary trajectories from geodesics on field space is computed in terms of the fluxes. It is shown that for some regions, they fulfill the recent proposed swampland criterion for multi‐field scenarios.
Meromorphic flux compactification Damian, Cesar; Loaiza-Brito, Oscar
The journal of high energy physics,
04/2017, Letnik:
2017, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A
bstract
We present exact solutions of four-dimensional Einstein’s equations related to Minkoswki vacuum constructed from Type IIB string theory with non-trivial fluxes. Following
1
,
2
we study a ...non-trivial flux compactification on a fibered product by a four-dimensional torus and a two-dimensional sphere punctured by 5- and 7-branes. By considering only 3-form fluxes and the dilaton, as functions on the internal sphere coordinates, we show that these solutions correspond to a family of supersymmetric solutions constructed by the use of G-theory. Meromorphicity on functions constructed in terms of fluxes and warping factors guarantees that flux and 5-brane contributions to the scalar curvature vanish while fulfilling stringent constraints as tadpole cancelation and Bianchi identities. Different Einstein’s solutions are shown to be related by U-dualities. We present three supersymmetric non-trivial Minkowski vacuum solutions and compute the corresponding soft terms. We also construct a non-supersymmetric solution and study its stability.
A
bstract
We study a Type IIB isotropic toroidal compactification with non-geometric fluxes. Under the assumption of a hierarchy on the moduli, an effective scalar potential is constructed showing a ...runaway direction on the real part of the Kähler modulus while the rest of the moduli are stabilized. For the effective model to be consistent it is required that displacements in the field space are finite. Infinite distances in field space would imply a breakdown in the hierarchy assumption on the moduli. In this context, the Swamp-land Distance Conjecture is satisfied suggesting the possibility of leaving or entering the Swampland by a parametric control of the fluxes. This is achieved upon allowing the non-geometric fluxes to take fractional values. In the process we are able to compute the cut-off scale below which the theory is valid, completely depending on the flux configuration. We also report on the appearance of a discrete spectrum of values for the string coupling at the level of the effective theory.
This paper presents a three-dimensional numerical modeling of a PEM fuel cell with tree-like flow field channels. Four different tree-like configurations are considered for the study based on a ...statistical analysis of the veins of the leaves of different trees. The number of bifurcations of the vein and their inclination are considered as parameters for the characterization. Four different configurations are the most recurrent, corresponding to one level of bifurcation at 37° and 74° and two levels of bifurcation at 37° and 74°. The model considers a complete solution of the mass, momentum, energy, and electrochemical equations. An entropy generation analysis is developed as a post processing once the solution of the models is obtained. Because new geometries for the channel configuration in the bipolar plates are introduced, special attention is considered for the entropy generation due to mass flow. Results indicate that the configuration with two levels of bifurcation at 37° is efficient at removing water from the cathode channels, resulting in a good current density production. In addition, a better performance of the PEM fuel cell (higher current density production and lower entropy production) is obtained by increasing the number of bifurcations.
•Four different tree-like flow field channel configurations are proposed for PEMFCs.•Configurations are based on analyses of the veins of the leaves of different trees.•An entropy generation analysis is developed for all the configurations proposed.•Increasing the number of bifurcations results in a better performance of the PEMFC.
In the present work, a spatio-temporal study of arsenic (As) concentration in groundwater and its impact in barley uptake is presented. The impact of As on barley is studied through the determination ...of its bioaccumulation in the soil-plant system, As uptake, as well as a correlation between As concentration in water and its temperature in the groundwater. For the groundwater, spatial and temporal variability of As concentration in central Mexico was determined through a geostatistical analysis using ordinary kriging. The results show that the variability of As in the ground water is correlated with its temperature (
R
2
> 0.83). The As accumulation in the structures of plant follows the order root > leaf > ear in concentration. The bioaccumulation factor BAF
T
suggests that As is mobilized to the aerial parts of the barely for both As concentrations used in the irrigation water. However, for As concentration lower than 25 μg L
−1
, the BAF
T
is lower than 0.57, suggesting that the amount of As in root is the same as that contained in the aerial parts; whereas, for higher As concentrations (from 170 to 250 μg L
−1
), the BAF
T
is around 0.92, indicating that the As is mainly contained in root. The spatial distribution of As concentration trend in groundwaters along the time is the same, which means high As concentration areas remain in the same groundwaters and these areas are presenting the highest water temperature. These results shall contribute to understand the bioaccumulation of As in barley and the As spatial variability in central Mexico.
The economic emission dispatch (EED) is a highly constrained nonlinear multiobjective optimization problem with a convex (or nonconvex) solution space. These characteristics and constraints make the ...EED a difficult problem to solve. Several approaches for a solution have been proposed, such as deterministic techniques, stochastic techniques, or a combination of both. This work presents the use of an algebraic (deterministic) technique, the numerical polynomial homotopy continuation (NPHC) method, to solve the EED problem. A comparison with the sequential quadratic programming (SQP) algorithm and the nondominated sorting genetic algorithm II (NSGA-II) is also presented. Results show that the NPHC algorithm finds all the roots (solutions) of the problem starting from any initial point and assures an accurate solution with a good convergence time. In addition, the NPHC algorithm provides a more accurate solution than the SQP algorithm and the NSGA-II.
We present a proposal to relate the de Sitter conjecture (dSC) with the time dependence of fluxes via the covariant entropy bound (CEB). By assuming an early phase of accelerated expansion where the ...CEB is satisfied, we take into account a contribution from time-dependent flux compactification to the four-dimensional entropy which establishes a bound on the usual slow-roll parameters ηH and ϵH. We also show an explicit calculation of entropy from a toroidal flux compactification, from a transition amplitude of time-dependent fluxes which allows us to determine the conditions on which the bounds on the slow-roll parameters are in agreement to the dSC.
Water contamination around the world is an increasing problem due to the presence of contaminants such as arsenic, fluoride, and chromium. The presence of such contaminants is related to either ...natural or anthropogenic processes. The above-mentioned problem has motivated the search for strategies to explore and develop technologies to remove these contaminants in water. Adsorption is a common process employed for such proposals due to its versatility, high adsorption capacity, and lower cost. In particular, graphene oxide is a material that is of special interest due to its physical and chemical properties such as surface area, porosity, pore size as well as removal efficiency for several contaminants. This review shows the advances, development, and perspectives of materials based on GO employed for the adsorption of contaminants such as arsenite, arsenate, fluoride, and hexavalent chromium. We provided a detailed discussion of the synthesis techniques and their relationship with the adsorption capacities and other physical properties as well as pH ranges employed to remove the contaminants. It is concluded that the adsorption capacity is not proportional to the surface area in all the cases; instead, the synthesis method, as well as the functional groups, play an important role. In particular, the sol-gel synthesis method shows better adsorption capacities.
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