scholarly journals Scalar-tensor theories within Asymptotic Safety

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Cristobal Laporte ◽  
Antonio D. Pereira ◽  
Frank Saueressig ◽  
Jian Wang
Keyword(s):  
Fixed Point ◽  
Background Field ◽  
High Energy ◽  
Field Method ◽  
Kinetic Term ◽  
Asymptotic Safety ◽  
Spacetime Curvature ◽  
Average Action ◽  
Initial Idea ◽  
First Time

Abstract Asymptotic Safety provides an elegant mechanism for obtaining a consistent high-energy completion of gravity and gravity-matter systems. Following the initial idea by Steven Weinberg, the construction builds on an interacting fixed point of the theories renormalization group (RG) flow. In this work we use the Wetterich equation for the effective average action to investigate the RG flow of gravity supplemented by a real scalar field. We give a non-perturbative proof that the subspace of interactions respecting the global shift-symmetry of the scalar kinetic term is closed under RG transformations. Subsequently, we compute the beta functions in an approximation comprising the Einstein-Hilbert action supplemented by the shift-symmetric quartic scalar self-interaction and the two lowest order shift-symmetric interactions coupling scalar-bilinears to the spacetime curvature. The computation utilizes the background field method with an arbitrary background, demonstrating that the results are manifestly background independent. Our beta functions exhibit an interacting fixed point suitable for Asymptotic Safety, where all matter interactions are non-vanishing. The presence of this fixed point is rooted in the interplay of the matter couplings which our work tracks for the first time. The relation of our findings with previous results in the literature is discussed in detail and we conclude with a brief outlook on potential phenomenological applications.

scholarly journals Asymptotically Safe Gravity-Fermion Systems on Curved Backgrounds

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 306
Author(s):  
Jesse Daas ◽  
Wouter Oosters ◽  
Frank Saueressig ◽  
Jian Wang
Keyword(s):  
Fixed Point ◽  
Fixed Points ◽  
Chiral Symmetry ◽  
Chiral Symmetry Breaking ◽  
Background Field ◽  
High Energy ◽  
Dirac Fermions ◽  
Dynamical Mechanism ◽  
Asymptotic Safety ◽  
Set Up

We set up a consistent background field formalism for studying the renormalization group (RG) flow of gravity coupled to Nf Dirac fermions on maximally symmetric backgrounds. Based on Wetterich’s equation, we perform a detailed study of the resulting fixed point structure in a projection including the Einstein–Hilbert action, the fermion anomalous dimension, and a specific coupling of the fermion bilinears to the spacetime curvature. The latter constitutes a mass-type term that breaks chiral symmetry explicitly. Our analysis identified two infinite families of interacting RG fixed points, which are viable candidates to provide a high-energy completion through the asymptotic safety mechanism. The fixed points exist for all values of Nf outside of a small window situated at low values Nf and become weakly coupled in the large Nf-limit. Symmetry-wise, they correspond to “quasi-chiral” and “non-chiral” fixed points. The former come with enhanced predictive power, fixing one of the couplings via the asymptotic safety condition. Moreover, the interplay of the fixed points allows for cross-overs from the non-chiral to the chiral fixed point, giving a dynamical mechanism for restoring the symmetry approximately at intermediate scales. Our discussion of chiral symmetry breaking effects provides strong indications that the topology of spacetime plays a crucial role when analyzing whether quantum gravity admits light chiral fermions.

scholarly journals SUPERGRAVITY IN 2+∊ DIMENSIONS

1994 ◽  
Vol 09 (31) ◽  
pp. 5415-5444 ◽  
Author(s):  
SHIN-ICHI KOJIMA ◽  
NORISUKE SAKAI ◽  
YOSHIAKI TANII
Keyword(s):  
Fixed Point ◽  
Dimensional Reduction ◽  
Background Field ◽  
Field Method ◽  
Three Dimensions ◽  
Supergravity Theory ◽  
Anomalous Dimensions ◽  
Gauge Fixing ◽  
Background Field Method

Supergravity theory in 2+∊ dimensions is studied. It is invariant under supertransformations in two and three dimensions. One-loop divergence is explicitly computed by the background field method and a nontrivial fixed point is found. In quantizing the supergravity, a gauge-fixing condition is devised which explicitly isolates conformal and superconformal modes. The renormalization of the gravitationally dressed operators is studied and their anomalous dimensions are computed. Problems in using the dimensional reduction are also examined.

scholarly journals GAUGE FIXING IDENTITY IN THE BACKGROUND FIELD METHOD OF QCD IN PURE GAUGE

2010 ◽  
Vol 25 (20) ◽  
pp. 3885-3898
Author(s):  
GOURANGA C. NAYAK
Keyword(s):  
Background Field ◽  
Heavy Ion ◽  
High Energy ◽  
Field Method ◽  
Coulomb Gauge ◽  
Factorization Theorem ◽  
Pure Gauge ◽  
Gauge Fixing ◽  
Covariant Gauge ◽  
Background Field Method

In this paper we derive a gauge fixing identity by varying the covariant gauge fixing term in [Formula: see text] in the background field method of QCD in pure gauge. Using this gauge fixing identity, we establish a relation between [Formula: see text] in QCD and [Formula: see text] in background field method of QCD in pure gauge. We show the validity of this gauge fixing identity, in general noncovariant and general Coulomb gauge fixings respectively. This gauge fixing identity is used to prove factorization theorem in QCD at high energy colliders and in nonequilibrium QCD at high energy heavy-ion colliders.

scholarly journals Mechanochemical Synthesis and Nitrogenation of the Nd1.1Fe10CoTi Alloy for Permanent Magnet

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3854
Author(s):  
Hugo Martínez Sánchez ◽  
George Hadjipanayis ◽  
Germán Antonio Pérez Alcázar ◽  
Ligia Edith Zamora Alfonso ◽  
Juan Sebastián Trujillo Hernández
Keyword(s):  
Mechanochemical Synthesis ◽  
Applied Field ◽  
Volume Fraction ◽  
Synthesis Method ◽  
High Energy ◽  
Direction Parallel ◽  
Best Value ◽  
Heat Treated ◽  
Bcc Phase ◽  
First Time

In this work, the mechanochemical synthesis method was used for the first time to produce powders of the nanocrystalline Nd1.1Fe10CoTi compound from Nd2O3, Fe2O3, Co and TiO2. High-energy-milled powders were heat treated at 1000 °C for 10 min to obtain the ThMn12-type structure. Volume fraction of the 1:12 phase was found to be as high as 95.7% with 4.3% of a bcc phase also present. The nitrogenation process of the sample was carried out at 350 °C during 3, 6, 9 and 12 h using a static pressure of 80 kPa of N2. The magnetic properties Mr, µ0Hc, and (BH)max were enhanced after nitrogenation, despite finding some residual nitrogen-free 1:12 phase. The magnetic values of a nitrogenated sample after 3 h were Mr = 75 Am2 kg–1, µ0Hc = 0.500 T and (BH)max = 58 kJ·m–3. Samples were aligned under an applied field of 2 T after washing and were measured in a direction parallel to the applied field. The best value of (BH)max~114 kJ·m–3 was obtained for 3 h and the highest µ0Hc = 0.518 T for 6 h nitrogenation. SEM characterization revealed that the particles have a mean particle size around 360 nm and a rounded shape.

scholarly journals Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanming Cai ◽  
Jiaju Fu ◽  
Yang Zhou ◽  
Yu-Chung Chang ◽  
Qianhao Min ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Active Sites ◽  
Theoretical Calculations ◽  
High Energy ◽  
Single Atom ◽  
Faradaic Efficiency ◽  
High Energy Barrier ◽  
Catalytic Sites ◽  
Electron Reduction ◽  
First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

scholarly journals Extraction new results of common fixed point theorems for $({T}, {\alpha }_{{s}}, {F})$-contraction of six mappings in a tripled b-metric space with an application of integral equations

2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Ghorban Khalilzadeh Ranjbar ◽  
Mohammad Esmael Samei
Keyword(s):  
Fixed Point ◽  
Common Fixed Point ◽  
Integral Equations ◽  
Metric Space ◽  
Fixed Point Theorems ◽  
Metric Spaces ◽  
Common Solution ◽  
Type Integral ◽  
First Time ◽  
Common Fixed Point Theorems

Abstract The aim of this work is to usher in tripled b-metric spaces, triple weakly $\alpha _{s}$ α s -admissible, triangular partially triple weakly $\alpha _{s}$ α s -admissible and their properties for the first time. Also, we prove some theorems about coincidence and common fixed point for six self-mappings. On the other hand, we present a new model, talk over an application of our results to establish the existence of common solution of the system of Volterra-type integral equations in a triple b-metric space. Also, we give some example to illustrate our theorems in the section of main results. Finally, we show an application of primary results.

scholarly journals NONCOMMUTATIVITY AND NON-ANTICOMMUTATIVITY PERTURBATIVE QUANTUM GRAVITY

2012 ◽  
Vol 27 (13) ◽  
pp. 1250075 ◽  
Author(s):  
MIR FAIZAL
Keyword(s):  
Quantum Gravity ◽  
Lagrangian Density ◽  
Background Field ◽  
Field Method ◽  
Gauge Fixing ◽  
Perturbative Quantum ◽  
Background Field Method

In this paper, we will study perturbative quantum gravity on supermanifolds with both noncommutativity and non-anticommutativity of spacetime coordinates. We shall first analyze the BRST and the anti-BRST symmetries of this theory. Then we will also analyze the effect of shifting all the fields of this theory in background field method. We will construct a Lagrangian density which apart from being invariant under the extended BRST transformations is also invariant under on-shell extended anti-BRST transformations. This will be done by using the Batalin–Vilkovisky (BV) formalism. Finally, we will show that the sum of the gauge-fixing term and the ghost term for this theory can be elegantly written down in superspace with a two Grassmann parameter.

OBSERVATIONAL CONSTRAINTS ON STRONG GRAVITY

2011 ◽  
Vol 20 (14) ◽  
pp. 2755-2760
Author(s):  
CHRIS DONE
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Field ◽  
Field Tests ◽  
High Energy ◽  
Observational Constraints ◽  
Tests Of General Relativity ◽  
Strong Gravity ◽  
Accretion Flows ◽  
Spacetime Curvature

Accretion onto a black hole transforms the darkest objects in the universe to the brightest. The high energy radiation emitted from the accretion flow before it disappears forever below the event horizon lights up the regions of strong spacetime curvature close to the black hole, enabling strong field tests of General Relativity. I review the observational constraints on strong gravity from such accretion flows, and show how the data strongly support the existence of such fundamental General Relativistic features of a last stable orbit and the event horizon. However, these successes also imply that gravity does not differ significantly from Einstein's predictions above the event horizon, so any new theory of quantum gravity will be very difficult to test.

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