scholarly journals Well-tempered Minkowski solutions in teleparallel Horndeski theory

2021 ◽  
Author(s):  
Reginald Christian Bernardo ◽  
Jackson Said ◽  
Maria Caruana ◽  
Stephen Appleby
Keyword(s):  
Particle Physics ◽  
Vacuum Energy ◽  
Vacuum State ◽  
Low Energy ◽  
Phase Portraits ◽  
Late Time ◽  
Field Equations ◽  
Linear Perturbations ◽  
Unique Method ◽  
Set Up

Abstract Well-tempering stands among the few classical methods of screening vacuum energy to deliver a late-time, low energy vacuum state. We build on the class of Horndeski models that admit a Minkowski vacuum state despite the presence of an arbitrarily large vacuum energy to obtain a much larger family of models in teleparallel Horndeski theory. We set up the routine for obtaining these models and present a variety of cases, all of which are able to screen a natural particle physics scale vacuum energy using degeneracy in the field equations. We establish that well-tempering is the unique method of utilizing degeneracy in Horndeski scalar-tensor gravity – and its teleparallel generalisation – that can accommodate self-tuned flat Minkowski solutions, when the explicit scalar field dependence in the action is minimal (a tadpole and a conformal coupling to the Ricci scalar). Finally, we study the dynamics of the well-tempered teleparallel Galileon. We generate its phase portraits and assess the attractor nature of the Minkowski vacuum under linear perturbations and through a phase transition of vacuum energy.

scholarly journals GRAVITY, COSMOLOGY AND PARTICLE PHYSICS WITHOUT THE COSMOLOGICAL CONSTANT PROBLEM

1998 ◽  
Vol 13 (19) ◽  
pp. 1583-1586 ◽  
Author(s):  
E. I. GUENDELMAN ◽  
A. B. KAGANOVICH
Keyword(s):  
Cosmological Constant ◽  
Particle Physics ◽  
Vacuum Energy ◽  
Vacuum State ◽  
Scalar Fields ◽  
Fine Tuning ◽  
Gauge Fields ◽  
Hierarchy Problem ◽  
Cosmological Constant Problem ◽  
First Order

This letter elucidates recent achievements of the "nongravitating vacuum energy (NGVE) theory" which has the feature that a shift of the Lagrangian density by a constant does not affect dynamics. In the first-order formalism, a constraint appears that enforces the vanishing of the cosmological constant Λ. Standard dynamics of gauge unified theories (including fermions) and their SSB appear if a four-index field strength condensate is present. At the vacuum state, there is exact balance (to zero) of the gauge fields condensate and the original scalar fields potential. As a result it is possible to combine the solution of the Λ problem with inflation and transition to a Λ=0 phase without fine tuning after a reheating period. The model opens new possibilities for a solution of the hierarchy problem.

scholarly journals The Swampland Conjectures: A Bridge from Quantum Gravity to Particle Physics

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 273
Author(s):  
Mariana Graña ◽  
Alvaro Herráez
Keyword(s):  
Effective Field Theories ◽  
Quantum Gravity ◽  
Particle Physics ◽  
Effective Field ◽  
Low Energy ◽  
Field Theories ◽  
Neutrino Masses ◽  
Higgs Potential ◽  
Photon Mass ◽  
Effective Theories

The swampland is the set of seemingly consistent low-energy effective field theories that cannot be consistently coupled to quantum gravity. In this review we cover some of the conjectural properties that effective theories should possess in order not to fall in the swampland, and we give an overview of their main applications to particle physics. The latter include predictions on neutrino masses, bounds on the cosmological constant, the electroweak and QCD scales, the photon mass, the Higgs potential and some insights about supersymmetry.

scholarly journals Growth and structure of multiphase gas in the cloud-crushing problem with cooling

2020 ◽  
Vol 501 (1) ◽  
pp. 1143-1159
Author(s):  
Vijit Kanjilal ◽  
Alankar Dutta ◽  
Prateek Sharma
Keyword(s):  
Mixing Layer ◽  
Cooling Time ◽  
Radiative Cooling ◽  
Late Time ◽  
Dense Gas ◽  
Mixed Gas ◽  
Continuous Growth ◽  
Dense Cloud ◽  
Set Up ◽  
Background Gas

ABSTRACT We revisit the problem of the growth of dense/cold gas in the cloud-crushing set-up with radiative cooling. The relative motion between the dense cloud and the diffuse medium produces a turbulent boundary layer of mixed gas with a short cooling time. This mixed gas may explain the ubiquity of the range of absorption/emission lines observed in various sources such as the circumgalactic medium and galactic/stellar/active galactic nucleus outflows. Recently, Gronke & Oh showed that the efficient radiative cooling of the mixed gas can lead to continuous growth of the dense cloud. They presented a threshold cloud size for the growth of dense gas that was contradicted by the more recent works of Li et al. & Sparre et al. These thresholds are qualitatively different as the former is based on the cooling time of the mixed gas whereas the latter is based on the cooling time of the hot gas. Our simulations agree with the threshold based on the cooling time of the mixed gas. We argue that the radiative cloud-crushing simulations should be run long enough to allow for the late-time growth of the dense gas due to cooling of the mixed gas but not so long that the background gas cools catastrophically. Moreover, the simulation domain should be large enough that the mixed gas is not lost through the boundaries. While the mixing layer is roughly isobaric, the emissivity of the gas at different temperatures is fundamentally different from an isobaric single-phase steady cooling flow.

scholarly journals REVIEW OF THE PHENOMENOLOGY OF NONCOMMUTATIVE GEOMETRY

2004 ◽  
Vol 19 (02) ◽  
pp. 179-204 ◽  
Author(s):  
I. HINCHLIFFE ◽  
N. KERSTING ◽  
Y. L. MA
Keyword(s):  
Electric Dipole ◽  
Particle Physics ◽  
Extra Dimensions ◽  
Linear Collider ◽  
Dipole Moments ◽  
High Energy ◽  
Low Energy ◽  
Electric Dipole Moments ◽  
The Status ◽  
High Energy Scattering

We present a pedagogical review of particle physics models that are based on the noncommutativity of space–time, [Formula: see text], with specific attention to the phenomenology these models predict in particle experiments either in existence or under development. We summarize results obtained for high energy scattering such as would occur, for example, in a future e+e-linear collider with [Formula: see text], as well as low energy experiments such as those pertaining to elementary electric dipole moments and other CP violating observables, and finally comment on the status of phenomenological work in cosmology and extra dimensions.

Hypersurface-homogeneous cosmological models with dynamical equation of state parameter in Lyra geometry

2015 ◽  
Vol 93 (10) ◽  
pp. 1100-1105 ◽  
Author(s):  
Shri Ram ◽  
S. Chandel ◽  
M.K. Verma
Keyword(s):  
Dynamical Equation ◽  
State Parameter ◽  
Lyra Geometry ◽  
Cosmological Models ◽  
Anisotropic Fluid ◽  
Late Time ◽  
Field Equations ◽  
Homogeneous Cosmological Models ◽  
Negative Constant ◽  
Equation Of State Parameter

The hypersurface homogeneous cosmological models are investigated in the presence of an anisotropic fluid in the framework of Lyra geometry. Exact solutions of field equations are obtained by applying a special law of variation for mean Hubble parameter that gives a negative constant value of the deceleration parameter. These solutions correspond to anisotropic accelerated expanding cosmological models that isotropize for late time even in the presence of anisotropic fluid. The anisotropy of the fluid also isotropizes at late time. Some physical and kinematical properties of the model are also discussed.

scholarly journals RADION POTENTIAL AND BRANE DYNAMICS

2001 ◽  
Vol 16 (24) ◽  
pp. 1583-1595 ◽  
Author(s):  
L. MERSINI
Keyword(s):  
Inflation Rate ◽  
Vacuum Energy ◽  
Density Perturbation ◽  
Scalar Fields ◽  
Fine Tuning ◽  
Late Time ◽  
Frw Universe ◽  
Strong Suppression ◽  
Dynamic Setting ◽  
The Universe

We examine the cosmology of Randall–Sundrum model in a dynamic setting where scalar fields are present in the bulk as well as the branes. This generates a mechanism similar to that of Goldberger–Wise for radion stabilization and the recovery of late-time cosmology features on the branes. Due to the induced radion dynamics, the inflating branes roll towards the minimum of the radion potential, thereby exiting inflation and reheating the universe. In the slow roll part of the potential, the TeV branes have maximum inflation rate and energy as their coupling to the radion and bulk modes have minimum suppression. Hence, when rolling down the steep end of the potential towards the stable point, the radion field (which appears as the inflaton of the effective 4-D theory in the branes) decays very fast and reheats the universe. This process results in a decrease of the brane's canonical vacuum energy, Λ4. However, at the minimum of the potential Λ4 is small but not necessarily zero and the fine-tuning issue remains. Density perturbation constraints introduce an upper bound on Λ4. Due to the large radion mass and strong suppression to the bulk modes, moduli problems and bulk reheating do not occur. The reheat temperature and a sufficient number of e-folding constraints for the brane-universe are also satisfied. The model therefore recovers the radiation dominated FRW universe.

scholarly journals On f(R) Theories in Two-Dimensional Spacetime

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
M. A. Ahmed
Keyword(s):  
Exact Solutions ◽  
Ricci Scalar ◽  
Two Dimensional ◽  
Field Equations ◽  
Dimensional Spacetime ◽  
Set Up

In recent years, theories in which the Einstein-Hilbert Lagrangian is replaced by a function f(R) of the Ricci Scalar have been extensively studied in four-dimensional spacetime. In this paper we carry out an analysis of such theories in two-dimensional spacetime with focus on cosmological implications. Solutions to the cosmological field equations are obtained and their properties are analysed. Inflationary solutions are also obtained and discussed. Quantization is then carried out, the Wheeler-DeWitt equation is set up, and its exact solutions are obtained.

scholarly journals Matching and running sensitivity in non-renormalizable inflationary models

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Jacopo Fumagalli ◽  
Marieke Postma ◽  
Melvin van den Bout
Keyword(s):  
Particle Physics ◽  
Higgs Field ◽  
Effective Field ◽  
Large Field ◽  
Tree Level ◽  
Planck Data ◽  
The Standard Model ◽  
Set Up ◽  
The One ◽  
Inflationary Models

Abstract Most of the inflationary models that are in agreement with the Planck data rely on the presence of non-renormalizable operators. If the connection to low energy particle physics is made, the renormalization group (RG) introduces a sensitivity to ultraviolet (UV) physics that can be crucial in determining the inflationary predictions. We analyse this effect for the Standard Model (SM) augmented with non-minimal derivative couplings to gravity. Our set-up reduces to the SM for small values of the Higgs field, and allows for inflation in the opposite large field regime. The one-loop beta functions in the inflationary region are calculated using a covariant approach that properly accounts for the non-trivial structure of the field space manifold. We run the SM parameters from the electroweak to the inflationary scale, matching the couplings of the different effective field theories at the boundary between the two regimes, where we also include threshold corrections that parametrize effects from UV physics. We then compute the spectral index and tensor-to-scalar ratio and find that RG flow corrections can be determinant: a scenario that is ruled out at tree level can be resurrected and vice versa.

scholarly journals Cosmological dynamics of f(R) models in dynamical system analysis

2020 ◽  
Vol 35 (22) ◽  
pp. 2050124
Author(s):  
Parth Shah ◽  
Gauranga C. Samanta
Keyword(s):  
Dynamical System ◽  
Asymptotic Behavior ◽  
Critical Points ◽  
System Analysis ◽  
Late Time ◽  
Field Equations ◽  
Acceleration Phase ◽  
First Case ◽  
Acceleration Of The Universe ◽  
The Universe

In this work we try to understand the late-time acceleration of the universe by assuming some modification in the geometry of the space and using dynamical system analysis. This technique allows to understand the behavior of the universe without analytically solving the field equations. We study the acceleration phase of the universe and stability properties of the critical points which could be compared with observational results. We consider an asymptotic behavior of two particular models [Formula: see text] and [Formula: see text] with [Formula: see text], [Formula: see text], [Formula: see text] for the study. As a first case we fix the value of [Formula: see text] and analyze for all [Formula: see text]. Later as second case, we fix the value of [Formula: see text] and calculation are done for all [Formula: see text]. At the end all the calculations for the generalized case have been shown and results have been discussed in detail.

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