scholarly journals Nonlocal inflationThis paper was prsented at the Theory CANADA 4 conference, held at the Centre de Recherches Mathématiques at the Université de Montréal, Québec, Canada on 4–7 June 2008.

2009 ◽  
Vol 87 (3) ◽  
pp. 189-194 ◽  
Author(s):  
Neil Barnaby
Keyword(s):  
Field Theory ◽  
Cosmic Microwave Background ◽  
String Field Theory ◽  
Initial Value Problem ◽  
High Derivative ◽  
Field Theories ◽  
Microwave Background ◽  
Initial Value ◽  
Nonlocal Field

We consider the possibility of realizing inflation in nonlocal field theories containing infinitely many derivatives. Such constructions arise naturally in string field theory and also in a number of toy models, such as the p-adic string. After reviewing the complications (ghosts and instabilities) that arise when working with high-derivative theories, we discuss the the initial value problem and perturbative stability of theories with infinitely many derivatives. Next, we examine the inflationary dynamics and phenomenology of such theories. Nonlocal inflation can proceed even when the potential is naively too steep and generically predicts large non-Gaussianity in the cosmic microwave background.

scholarly journals Mapping between Witten and lightcone string field theories

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Theodore Erler ◽  
Hiroaki Matsunaga
Keyword(s):  
Field Theory ◽  
String Field Theory ◽  
Bosonic String ◽  
Field Theories

Abstract We propose a transformation between the off-shell field variables of Witten’s open bosonic string field theory and the traditional lightcone string field theory of Kaku and Kikkawa, based on Mandelstam’s interacting string picture. This is accomplished by deforming the Witten vertex into lightcone cubic and quartic vertices, followed by integrating out the ghost and lightcone oscillator excitations from the string field. Surprisingly, the last step does not alter the cubic and quartic interactions and does not generate effective vertices, and leads precisely to Kaku and Kikkawa’s lightcone string field theory.

scholarly journals Cosmic Microwave Background from Effective Field Theory †

Universe ◽  
2019 ◽  
Vol 5 (6) ◽  
pp. 155
Author(s):  
Sayantan Choudhury
Keyword(s):  
Field Theory ◽  
Cosmic Microwave Background ◽  
Effective Field Theory ◽  
Vacuum State ◽  
Effective Field ◽  
De Sitter ◽  
Microwave Background ◽  
Slow Roll ◽  
Point Correlation ◽  
Single Field

In this work, we study the key role of generic Effective Field Theory (EFT) framework to quantify the correlation functions in a quasi de Sitter background for an arbitrary initial choice of the quantum vacuum state. We perform the computation in unitary gauge, in which we apply the St u ¨ ckelberg trick in lowest dimensional EFT operators which are broken under time diffeomorphism. In particular, using this non-linear realization of broken time diffeomorphism and truncating the action by considering the contribution from two derivative terms in the metric, we compute the two-point and three-point correlations from scalar perturbations and two-point correlation from tensor perturbations to quantify the quantum fluctuations observed in the Cosmic Microwave Background (CMB) map. We also use equilateral limit and squeezed limit configurations for the scalar three-point correlations in Fourier space. To give future predictions from EFT setup and to check the consistency of our derived results for correlations, we use the results obtained from all classes of the canonical single-field and general single-field P ( X , ϕ ) model. This analysis helps us to fix the coefficients of the relevant operators in EFT in terms of the slow-roll parameters and effective sound speed. Finally, using CMB observations from Planck we constrain all these coefficients of EFT operators for the single-field slow-roll inflationary paradigm.

scholarly journals PHYSICAL DEGREES OF FREEDOM IN 2D STRING FIELD THEORIES

1992 ◽  
Vol 07 (37) ◽  
pp. 3479-3486
Author(s):  
NORISUKE SAKAI ◽  
YOSHIAKI TANII
Keyword(s):  
Field Theory ◽  
Master Equation ◽  
String Field Theory ◽  
Degrees Of Freedom ◽  
Field Theories ◽  
Relative Cohomology ◽  
Component Decomposition ◽  
The Absolute

States in the absolute (semi-relative) cohomology but not in the relative cohomology are examined through the component decomposition of the string field theory action for the 2D string. It is found that they are auxiliary fields without kinetic terms, but are important for instance in the master equation for the Ward-Takahashi identities. The ghost structure is analyzed in the Siegel gauge, but it is noted that the absolute (semi-relative) cohomology states are lost.

scholarly journals Tree-level S-matrix of superstring field theory with homotopy algebra structure

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Hiroshi Kunitomo
Keyword(s):  
Field Theory ◽  
String Field Theory ◽  
Heterotic String ◽  
Field Theories ◽  
Tree Level ◽  
Algebra Structure ◽  
Type Ii ◽  
S Matrix ◽  
Homotopy Algebra

Abstract We show that the tree-level S-matrices of the superstring field theories based on the homotopy-algebra structure agree with those obtained in the first-quantized formulation. The proof is given in detail for the heterotic string field theory. The extensions to the type II and open superstring field theories are straightforward.

scholarly journals PAIR PRODUCTION IN A STRONG ELECTRIC FIELD: AN INITIAL VALUE PROBLEM IN QUANTUM FIELD THEORY

1993 ◽  
Vol 02 (02) ◽  
pp. 333-380 ◽  
Author(s):  
Y. KLUGER ◽  
J.M. EISENBERG ◽  
B. SVETITSKY
Keyword(s):  
Field Theory ◽  
Electric Field ◽  
Initial Value Problem ◽  
Particle Creation ◽  
Mean Field Approximation ◽  
Time Behavior ◽  
Initial Value ◽  
Plasma Oscillations ◽  
Physical Features ◽  
Creation Rate

We review recent achievements in the solution of the initial-value problem for quantum backreaction in scalar and spinor QED. The problem is formulated and solved in the semiclassical mean-field approximation for a homogeneous, time-dependent electric field. Our primary motivation in examining backreaction has to do with applications to theoretical models of production of the quark-gluon plasma though we here address practicable solutions for backreaction in general. We review the application of the method of adiabatic regularization to the Klein-Gordon and Dirac fields in order to renormalize the expectation value of the current and derive a finite coupled set of ordinary differential equations for the time evolution of the system. Three time scales are involved in the problem and therefore caution is needed to achieve numerical stability for this system. Several physical features like plasma oscillations and plateaus in the current appear in the solution. From the plateau of the electric current one can estimate the number of pairs before the onset of plasma oscillations, while the plasma oscillations themselves yield the number of particles from the plasma frequency. We compare the field-theory solution to a simple model based on a relativistic Boltzmann-Vlasov equation with a particle production source term inferred from the Schwinger particle creation rate and a Pauli-blocking (or Bose-enhancement) factor. This model reproduces very well the time behavior of the electric field and the creation rate of charged pairs of the semiclassical calculation. It therefore provides a simple intuitive understanding of the nature of the solution since nearly all the physical features can be expressed in terms of the classical distribution function.

scholarly journals RECENT DEVELOPMENTS IN D=2 STRING FIELD THEORY

1994 ◽  
Vol 09 (18) ◽  
pp. 3103-3141 ◽  
Author(s):  
MICHIO KAKU
Keyword(s):  
Field Theory ◽  
String Field Theory ◽  
Correlation Functions ◽  
Two Dimensions ◽  
Field Theories ◽  
Fermion Field ◽  
Free Fermion ◽  
Temporal Gauge ◽  
Recent Developments ◽  
The Relationship

We review the recent developments in the construction of string field theory in two dimensions. We analyze the bewildering number of string field theories that have been proposed, all of which correctly reproduce the correlation functions of two-dimensional string theory. These include (1) free fermion field theory, (2) collective string field theory, (3) temporal gauge string field theory and (4) nonpolynomial string field theory. We will analyze discrete states, the ω(∞) symmetry, and correlation functions in terms of these different string field theories. We will also comment on the relationship between these field theories, which is still not well understood.

LOOP CALCULATIONS IN TWO-DIMENSIONAL NONLOCAL FIELD THEORIES

1992 ◽  
Vol 07 (23) ◽  
pp. 5891-5915 ◽  
Author(s):  
M.T. GRISARU ◽  
P. VAN NIEUWENHUIZEN
Keyword(s):  
Field Theory ◽  
Local Field ◽  
Momentum Space ◽  
Field Theories ◽  
Two Dimensional ◽  
Local Field Theory ◽  
Nonlocal Action ◽  
Nonlocal Field

We perform one-loop calculations in chiral induced W3 gravity in momentum space. Unlike a previous one-loop calculation in x space, which reduced the problem to one in local field theory, we work directly with the nonlocal action. We use Polyakov’s exponential regularization, and obtain agreement with the x-space calculation. We discuss the extension of our methods to higher-loop calculations in more-general chiral nonlocal field theories.

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