Large-field Models Research Articles

An Analysis of Relationship Quality and Loyalty Between Farmers and Agribusiness Companies in the Rice Industry: Using Multi-Group Analysis

Rice is an important agricultural product in Vietnam; however, the rice industry faces several challenges, particularly weak linkages between farmers and enterprises. The Vietnamese government has introduced the Large Field Model (LFM) program to improve cooperation between farmers and agribusiness companies. Despite these efforts, its implementation remains limited, and contract violations are common. This study investigated the factors affecting relationship quality (RQ) and loyalty (LO) between farmers and agricultural companies in the LFM, focusing on comparing cooperative and non-cooperative participating farmers. Using the Partial Least Squares–Multi-Group Analysis (PLS-MGA) method, this study assessed the different effects of factors such as price satisfaction (PS), payment terms (PTs), and support policies (SPs) on RQ and LO among two groups. The findings indicated that RQ has a stronger influence on LO in farmers with cooperative participation than those who exhibit non-cooperative participation. PS was the most significant factor influencing RQ in both groups, whereas PT was influential only for cooperative participating farmers. SP did not significantly affect RQ in either group. Finally, agricultural companies and policymakers should strengthen partnership management in agricultural supply chains by addressing gaps in support policies, developing appropriate pricing strategies, being flexible in negotiating payment terms, and improving the legal framework related to contract enforcement.

KSW criterion in large field models

KSW criterion in large field models

Almost relevant corrections for direct measurements of electron’s g factor

We revisit the observable used for the direct measurements of the electron's $g$ factor. This is done by considering the sub-leading effects of the large magnetic background field and virtual Standard Model processes. We find substantial corrections to the Landau levels of the electron. Implications for the observed magnetic moment and the tension between direct and indirect measurement are discussed.

Analytic correlation of inflationary potential to power spectrum shape: limits of validity, and `no-go' for small field model analytics

The primordial power spectrum informs the possible inflationary histories of our universe. Given a power spectrum, the ensuing cosmic microwave background is calculated and compared to the observed one. Thus, one focus of modern cosmology is building well-motivated inflationary models that predict the primordial power spectrum observables. The common practice uses analytic terms for the scalar spectral index ns and the index running α, forgoing the effort required to evaluate the model numerically. However, the validity of these terms has never been rigorously probed and relies on perturbative methods, which may lose their efficacy for large perturbations. The requirement for more accurate theoretical predictions becomes crucial with the advent of highly sensitive measuring instruments. This paper probes the limits of the perturbative treatment that connects inflationary potential parameters to primordial power spectrum observables. We show that the validity of analytic approximations of the scalar index roughly respects the large-field/small-field dichotomy. We supply an easily calculated measure for relative perturbation amplitude and show that, for large field models, the validity of analytical terms extends to ∼ 3% perturbation relative to a power-law inflation model.Conversely, the analytical treatment loses its validity for small field models with as little as 0.1% perturbation relative to the small-field test-case. By employing the most general artificial neural networks and multinomial functions up to the twentieth degree and demonstrating their shortcomings, we show that no reasonable and universal analytic expressions correlating small field models to the observables they yield exists.Finally, we discuss the possible implications of this work and supply the validity heuristic for large and small field models.

Sustainable farming techniques and farm size for rice smallholders in the Vietnamese Mekong Delta: A slack-based technical efficiency approach

Small farm size and fragmented land are considered constraining agricultural development. This study uses the Vietnam Household Living Standard Survey 2016 (VHLSS 2016) dataset to measure the technical efficiency of rice smallholders and its determinants, including farm size, in the Mekong Delta. Data envelopment analysis was employed to examine efficiency scores in the first stage based on data of 506 paddy farms. The overall efficiency calculated through slack-based measure was low at 0.59 and the input slacks were quite large. This indicated that local farmers have not been using their resources efficiently in producing paddy. Further, farms smaller than 2 ha faced low overall efficiency at 54% and higher slacks in terms of all input types. The second-stage Tobit result showed that all types of efficiency could be improved if farmers expanded their farm size and reduced the over-use of inputs. Thus, enabling small farms to achieve economies of scale through collective farming in the Large Field Model (LFM) will be critical for upgrading production efficiency and reducing slacks as labor costs rise and natural resources are constrained. It is recommended that farmers should follow strictly eco-friendly farming packages in order to reduce their current excessive usage of seed cost by 28 USD/ha, pesticides by 61 USD/ha, and fertilizers by 155 kg/ha to reach efficient production frontier. The government needs to take measures to replicate and closely monitor climate smart agriculture programs in large-scale production to improve the overall efficiency of paddy sector, in addition to the important goal of protecting the environment and natural resources of the region. Availability of data and materialsThe VHLSS 2016 questionnaire section and dataset analyzed in this study are available from the corresponding author on reasonable request.

Small free field inflation in higher curvature gravity

Within General Relativity, a minimally coupled scalar field governed by a quadratic potential is able to produce an accelerated expansion of the universe provided its value and excursion are larger than the Planck scale. This is an archetypical example of the so called large field inflation models. We show that by including higher curvature corrections to the gravitational action in the form of the Geometric Inflation models, it is possible to obtain accelerated expansion with a free scalar field whose values are well below the Planck scale, thereby turning a traditional large field model into a small field one. We provide the conditions the theory has to satisfy in order for this mechanism to operate, and we present two explicit models illustrating it. Finally, we present some open questions raised by this scenario in which inflation takes place completely in a higher curvature dominated regime, such as those concerning the study of perturbations.

Modulations in Spectra of Galactic Gamma-ray sources as a result of photon-ALPs mixing.

Axion like particles (ALPs) are fundamental pseudo scalar particles with properties similar to Axions which are a well-known extensions of the standard model to solve the strong CP problem in Quantum Chromodynamics. ALPs can oscillate into photons and vice versa in the presence of an external tranversal magnetic field. This oscillation of photon and ALPs could have important implications for astronomical observations, i.e. a characteristic energy dependent attenuation in Gamma ray spectra for astrophysical sources. Here we have revisited the opportunity to search Photon-ALPs coupling in the disappearance channel. We use eight years of Fermi Pass 8 data of a selection of promising galactic Gamma-ray source candidates and study the modulation in the spectra in accordance with Photon-ALPs mixing and estimate best fit values of the parameters i.e. Photon-ALPs coupling constant (gʱγγ) and ALPs mass(mα). For the magnetic field we use large scale galactic magnetic field models based on Faraday rotation measurements and we have also studied the survival probability of photons in the Galactic plane.

Onset of inflation amid backreaction from inhomogeneities

We analyze the onset of inflation for a simple single-field model when the system begins with significant inhomogeneities on length-scales shorter than the initial Hubble radius. We incorporate certain nonlinear interactions among the coupled degrees of freedom by using the nonperturbative Hartree approximation. Consistent with recent, more computationally intensive numerical-relativity studies, we find inflation to be robust for large-field models, even when the system begins with significant structure on sub-Hubble scales. We consider the space of initial conditions $(\varphi (t_0), \dot{\varphi} (t_0))$, where $\varphi$ is the vacuum expectation value of the quantized field that drives inflation. Although some regions of $(\varphi (t_0), \dot{\varphi} (t_0))$ that would have yielded sufficient inflation in the absence of inhomogeneities fail to do so when backreaction from inhomogeneities is incorporated, an equal volume of such regions succeeds in producing sufficient inflation which did not do so in the absence of inhomogeneities. For large-field models, in other words, the total volume of the space of initial conditions $(\varphi (t_0), \dot{\varphi} (t_0))$ that yields sufficient inflation is {\it conserved} when we incorporate nonlinear backreaction from inhomogeneities, compared to the case in which inhomogeneities are neglected.

Small field models of inflation that predict a tensor-to-scalar ratio r=0.03

Future observations of the cosmic microwave background (CMB) polarization are expected to set an improved upper bound on the tensor-to-scalar ratio of $r\lesssim 0.03$. Recently, we showed that small field models of inflation can produce a significant primordial gravitational wave signal. We constructed viable small field models that predict a value of $r$ as high as $0.01$. Models that predict higher values of $r$ are more tightly constrained and lead to larger field excursions. This leads to an increase in tuning of the potential parameters and requires higher levels of error control in the numerical analysis. Here, we present viable small field models which predict $r=0.03$. We further find the most likely candidate among these models which fit the most recent Planck data while predicting $r= 0.03$. We thus demonstrate that this class of small field models is an alternative to the class of large field models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected to provide experimental evidence to support or refute our predictions.

Geometrical destabilization, premature end of inflation and Bayesian model selection

By means of Bayesian techniques, we study how a premature ending of inflation, motivated by geometrical destabilization, affects the observational evidences of typical inflationary models. Large-field models are worsened, and inflection point potentials are drastically improved for a specific range of the field-space curvature characterizing the geometrical destabilization. For other models we observe shifts in the preferred values of the model parameters. For quartic hilltop models for instance, contrary to the standard case, we find preference for theoretically natural sub-Planckian hill widths. Eventually, the Bayesian ranking of models becomes substantially reordered with a premature end of inflation. Such a phenomenon also modifies the constraints on the reheating expansion history, which has to be properly accounted for since it determines the position of the observational window with respect to the end of inflation. Our results demonstrate how the interpretation of cosmological data in terms of fundamental physics is considerably modified in the presence of premature end of inflation mechanisms.

Initial conditions for inflation — A short review

I give a brief review of the status of research on the nature of initial conditions required to obtain a period of cosmological inflation. It is shown that there is good evidence that in the case of large field models, the inflationary slow-roll trajectory is a local attractor in initial condition space, whereas it is not in the case of small field models.

Hemispherical anomaly from asymmetric initial states

We investigate if the hemispherical asymmetry in the CMB is produced from "asymmetric" excited initial condition. We show that in the limit where the deviations from the Bunch-Davies vacuum is large and the scale of new physics is maximally separated from the inflationary Hubble parameter, the primordial power spectrum is modulated only by position dependent dipole and quadrupole terms. Requiring the dipole contribution in the power spectrum to account for the observed power asymmetry, $A=0.07\pm0.022$, we show that the amount of quadrupole terms is roughly equal to $A^2$. The {\it mean} local bispectrum, which gets enhanced for the excited initial state, is within the $1\sigma$ bound of Planck 2015 results for a large field model, $f_{\rm NL}\simeq 4.17$, but is reachable by future CMB experiments. The amplitude of the local non-gaussianity modulates around this mean value, depending on the angle that the correlated patches on the 2d CMB surface make with the preferred direction. The amount of variation minimizes for the configuration in which the short and long wavelengths modes are around the preferred pole and $|\vec k_3|\approx |\vec k_{l\approx10}|\ll |\vec k_1|\approx |\vec k_2|\approx |\vec k_{l\approx2500}|$ with $f_{\rm NL}^{\rm min}\approx 3.64 $. The maximum occurs when these modes are at the antipode of the preferred pole, $f_{\rm NL}^{\rm max}\approx 4.81$ . The difference of non-gaussianity between these two configurations is as large as $\simeq 1.17$ which can be used to distinguish this scenario from other scenarios that try to explain the observed hemispherical asymmetry.

Modular invariant inflation

Modular invariance is a striking symmetry in string theory, which may keep stringy corrections under control. In this paper, we investigate a phenomenological consequence of the modular invariance, assuming that this symmetry is preserved as well as in a four dimensional (4D) low energy effective field theory. As a concrete setup, we consider a modulus field T whose contribution in the 4D effective field theory remains invariant under the modular transformation and study inflation drived by T. The modular invariance restricts a possible form of the scalar potenntial. As a result, large field models of inflation are hardly realized. Meanwhile, a small field model of inflation can be still accomodated in this restricted setup. The scalar potential traced during the slow-roll inflation mimics the hilltop potential Vht, but it also has a non-negligible deviation from Vht. Detecting the primordial gravitational waves predicted in this model is rather challenging. Yet, we argue that it may be still possible to falsify this model by combining the information in the reheating process which can be determined self-completely in this setup.

On the validity of the perturbative description of axions during inflation

Axions play a central role in many realizations of large field models of inflation and in recent alternative mechanisms for generating primordial tensor modes in small field models. If these axions couple to gauge fields, the coupling produces a tachyonic instability that leads to an exponential enhancement of the gauge fields, which in turn can decay into observable scalar or tensor curvature perturbations. Thus, a fully self-consistent treatment of axions during inflation is important, and in this work we discuss the perturbative constraints on axions coupled to gauge fields. We show how the recent proposal of generating tensor modes through these alternative mechanisms is in tension with perturbation theory in the in-in formalism. Interestingly, we point out that the constraints are parametrically weaker than one would estimate based on naive power counting of propagators of the gauge field. In the case of non-Abelian gauge fields, we derive new constraints on the size of the gauge coupling, which apply also in certain models of natural large field inflation, such as alignment mechanisms.

Constraining brane inflationary magnetic field from cosmoparticle physics after Planck

In this article, I have studied the cosmological and particle physics constraints on a generic class of large field ($|\Delta\phi|>M_{p}$) and small field ($|\Delta\phi<M_{p}$) models of brane inflationary magnetic field from: (1) tensor-to-scalar ratio ($r$), (2) reheating, (3) leptogenesis and (4) baryogenesis in case of Randall-Sundrum single braneworld gravity (RSII) framework. I also establish a direct connection between the magnetic field at the present epoch ($B_{0}$) and primordial gravity waves ($r$), which give a precise estimate of non-vanishing CP asymmetry ($\epsilon_{CP}$) in leptogenesis and baryon asymmetry ($\eta_{B}$) in baryogenesis scenario respectively. Further assuming the conformal invariance to be restored after inflation in the framework of RSII, I have explicitly shown that the requirement of the sub-dominant feature of large scale coherent magnetic field after inflation gives two fold non-trivial characteristic constraints- on equation of state parameter ($w$) and the corresponding energy scale during reheating ($\rho^{1/4}_{rh}$) epoch. Hence giving the proposal for avoiding the contribution of back-reaction from the magnetic field I have established a bound on the generic reheating characteristic parameter ($R_{rh}$) and its rescaled version ($R_{sc}$), to achieve large scale magnetic field within the prescribed setup and further apply the CMB constraints as obtained from recently observed Planck 2015 data and Planck+BICEP2+Keck Array joint constraints. Using all these derived results I have shown that it is possible to put further stringent constraints on various classes of large and small field inflationary models to break the degeneracy between various cosmological parameters within the framework of RSII. Finally, I have studied the consequences from two specific models of brane inflation- monomial and hilltop.

String cosmology — Large-field inflation in string theory

This is a short review of string cosmology. We wish to connect string-scale physics as closely as possible to observables accessible to current or near-future experiments. Our possible best hope to do so is a description of inflation in string theory. The energy scale of inflation can be as high as that of Grand Unification (GUT). If this is the case, this is the closest we can possibly get in energy scales to string-scale physics. Hence, GUT-scale inflation may be our best candidate phenomenon to preserve traces of string-scale dynamics. Our chance to look for such traces is the primordial gravitational wave, or tensor mode signal produced during inflation. For GUT-scale inflation this is strong enough to be potentially visible as a B-mode polarization of the cosmic microwave background (CMB). Moreover, a GUT-scale inflation model has a trans-Planckian excursion of the inflaton scalar field during the observable amount of inflation. Such large-field models of inflation have a clear need for symmetry protection against quantum corrections. This makes them ideal candidates for a description in a candidate fundamental theory like string theory. At the same time the need of large-field inflation models for UV completion makes them particularly susceptible to preserve imprints of their string-scale dynamics in the inflationary observables, the spectral index ns and the fractional tensor mode power r. Hence, we will focus this review on axion monodromy inflation as a mechanism of large-field inflation in string theory.

Dynamical fractional chaotic inflation

Chaotic inflation based on a simple monomial scalar potential, $V(\ensuremath{\phi})\ensuremath{\propto}{\ensuremath{\phi}}^{p}$, is an attractive large-field model of inflation capable of generating a sizable tensor-to-scalar ratio $r$. Therefore, assuming that future cosmic microwave background observations will confirm the large $r$ value reported by BICEP2, it is important to determine what kind of dynamical mechanism could possibly endow the inflaton field with such a simple effective potential. In this paper, we answer this question in the context of field theory, i.e. in the framework of dynamical chaotic inflation, where strongly interacting supersymmetric gauge dynamics around the scale of grand unification dynamically generate a fractional power-law potential via the quantum effect of dimensional transmutation. In constructing explicit models, we significantly extend our previous work, as we now consider a large variety of possible underlying gauge dynamics and relax our conditions on the field content of the model. This allows us to realize almost arbitrary rational values for the power $p$ in the inflaton potential. The present paper may hence be regarded as a first step toward a more complete theory of dynamical chaotic inflation.

How manye-folds should we expect from high-scale inflation?

We address the issue of how many $e$-folds we would naturally expect if inflation occurred at an energy scale of order $10^{16}$ GeV. We use the canonical measure on trajectories in classical phase space, specialized to the case of flat universes with a single scalar field. While there is no exact analytic expression for the measure, we are able to derive conditions that determine its behavior. For a quadratic potential $V(\phi)=m^{2}\phi^{2}/2$ with $m=2\times10^{13}$ GeV and cutoff at $M_{{\rm Pl}}=2.4\times10^{18}$ GeV, we find an expectation value of $2\times10^{10}$ $e$-folds on the set of Friedmann-Robertson-Walker trajectories. For cosine inflation $V(\phi)=\Lambda^{4}[1-\cos(\phi/f)]$ with $f=1.5\times10^{19}$ GeV, we find that the expected total number of $e$-folds is 50, which would just satisfy the observed requirements of our own Universe; if $f$ is larger, more than 50 $e$-folds are generically attained. We conclude that one should expect a large amount of inflation in large-field models and more limited inflation in small-field (hilltop) scenarios.

Consistency relations for large-field inflation

Consistency relations for chaotic inflation with a monomial potential and natural inflation and hilltop inflation are given which involve the scalar spectral index $n_s$, the tensor-to-scalar ratio $r$ and the running of the spectral index $\alpha$. The measurement of $\alpha$ with $O(10^{-3})$ and the improvement in the measurement of $n_s$ could discriminate monomial model from natural/hilltop inflation models. A consistency region for general large field models is also presented.

Compatibility of Planck and BICEP2 results in light of inflation

We investigate the implications for inflation of the detection of B-modes polarization in the Cosmic Microwave Background (CMB) by BICEP2. We show that the hypothesis of primordial origin of the measurement is only favored by the first four bandpowers, while the others would prefer unreasonably large values of the tensor-to-scalar ratio. Using only those four bandpowers, we carry out a complete analysis in the cosmological and inflationary slow-roll parameter space using the BICEP2 polarization measurements alone and extract the Bayesian evidences and complexities for all the Encyclopaedia Inflationaris models. This allows us to determine the most probable and simplest BICEP2 inflationary scenarios. Although this list contains the simplest monomial potentials, it also includes many other scenarios, suggesting that focusing model building efforts on large field models only is unjustified at this stage. We demonstrate that the sets of inflationary models preferred by Planck alone and BICEP2 alone are almost disjoint, indicating a clear tension between the two data sets. We address this tension with a Bayesian measure of compatibility between BICEP2 and Planck. We find that for models favored by Planck the two data sets tend to be incompatible, whereas there is a moderate evidence of compatibility for the BICEP2 preferred models. As a result, it would be premature to draw any conclusion on the best Planck models, such as Starobinsky and/or Kahler moduli inflation. For the subset of scenarios not exhibiting data sets incompatibility, we update the evidences and complexities using both data sets together.