Comparing brane inflation to WMAP

Bean, Rachel; Shandera, Sarah; Tye, S.‐H. Henry; Xu, Jiajun

doi:10.1088/1475-7516/2007/05/004

Cited by 130 publications

(205 citation statements)

References 65 publications

(169 reference statements)

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“…While it is plausible that somewhat larger Lorentz factors could arise very near the tip of the throat, which was not directly studied in [240], the problem of backreaction becomes severe in this regime, as discussed below. The earlier analysis [708] worked with a simpler model of the potential, but arrived at compatible conclusions: 39 Identifying an alternative setting for DBI inflation in a string compactification would be very interesting, and would undoubtedly lead to modified microphysical constraints, but we are not aware of any complete example.…”

Section: Microphysical Constraintsmentioning

confidence: 82%

“…The precise functional forms of the warp factor e 4A(φ) and the potential V (φ) determine the details of the phenomenology of DBI inflation (see [668,708]). As a generalization of the AdS background (5.91), we will use Calabi-Yau cones that approximate finite warped throat regions attached to type IIB flux compactifications.…”

Section: Dirac-born-infeld Inflationmentioning

confidence: 99%

“…Analytical [38,40] and numerical [668,708] studies have shown that for suitable potentials V (φ), the DBI Lagrangian (5.92) can indeed support an inflationary phase in which the non-trivial kinetic term plays a crucial role. However, before describing the phenomenology of DBI inflation, one should first ask whether the DBI Lagrangian (5.92) gives an accurate and consistent representation of the physics of a relativistic D3-brane.…”

Section: Dirac-born-infeld Inflationmentioning

confidence: 99%

“…In extreme cases, this increased force can compel the D3-brane to be relativistic: [708] found that a DBI phase arose for Vol(X 5 ) 10 −17 . However, it is highly implausible that such a throat can be embedded in a consistent compactification, and moreover, even if this issue is overlooked, the examples of [708] are incompatible either with observations or with the microphysical bound of [243].…”

Section: Microphysical Constraintsmentioning

confidence: 99%

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Inflation and String Theory

2015

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Section: Microphysical Constraintsmentioning

confidence: 82%

Section: Dirac-born-infeld Inflationmentioning

confidence: 99%

Section: Dirac-born-infeld Inflationmentioning

confidence: 99%

Section: Microphysical Constraintsmentioning

confidence: 99%

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Inflation and String Theory

2015

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“…However, since f NL is roughly the ratio of the 3-point function with respect to the square of the power spectrum, one sees that f NL is now reduced by the factor 1 T 2 RS . The so-called UV model of DBI inflation is under strong observational pressure because it generates a high level of non-Gaussianities that exceed the experimental bound [18,19]. We stress that their reduction by multiple-field effects may be very important for model building.…”

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confidence: 94%

Primordial Fluctuations and Non-Gaussianities in Multifield Dirac-Born-Infeld Inflation

et al. 2008

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We study Dirac-Born-Infeld inflation models with multiple scalar fields. We show that the adiabatic and entropy modes propagate with a common effective sound speed and are thus amplified at the sound horizon crossing. In the small sound speed limit, we find that the amplitude of the entropy modes is much higher than that of the adiabatic modes. We show that this could strongly affect the observable curvature power spectrum as well as the amplitude of non-Gaussianities, although their shape remains as in the single-field Dirac-Born-Infeld case. The past decade has seen an accumulation of cosmological data of increasing precision. Together with future experiments planned to measure the cosmic microwave background (CMB) fluctuations with yet further accuracy, we may be able to piece together more clues about early Universe physics. In parallel with this observational effort, there has been tremendous progress in recent years in the construction of early Universe models in the framework of high energy physics and string theory.A particularly interesting class of models based on string theory is known as Dirac-Born-Infeld (DBI) inflation [1,2], associated with the motion of a D3-brane in a higherdimensional background spacetime. The characteristic of DBI inflation, and that which gives it its name, is that the action is of the Dirac-Born-Infeld type and thus contains nontrivial kinetic terms. Most studies of DBI inflation models (or even of string-based inflationary models) have so far concentrated on a single-field description meaning, in the DBI case, that the inflaton corresponds to a radial coordinate of the brane in the extra dimensions. Taking into account the ''angular'' coordinates of the brane naturally leads to a multifield description since each brane coordinate in the extra dimensions gives rise to a scalar field from the effective four-dimensional point of view. This setup has started to be explored only very recently [3,4].In this Letter, we show that the multifield DBI action contains some terms, higher order in spacetime gradients and vanishing in the homogeneous case, which have been overlooked. The inclusion of these terms leads to drastic consequences on the primordial fluctuations generated in these types of models. The scalar-type perturbations in multifield models can be divided into (instantaneous) adiabatic modes, fluctuations along the trajectory in field space, and entropy modes which are orthogonal to the former [5]. In contrast with previous expectations, we show that, in DBI models, these two classes of modes propagate with the same speed, namely, an effective speed of sound c s smaller than the speed of light. As a consequence, the amplification of quantum fluctuations occurs at the sound horizon crossing for both types of modes. Moreover, when c s 1, this leads to an enhancement of the amplitude of the entropy modes with respect to that of the usual adiabatic modes. As primordial non-Gaussianities -potentially detectable in forthcoming experiments if strong enough-discriminate between v...

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Phenomenological aspects of type IIB flux compactifications

Pajer

2009

Fortschritte der Physik

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The purpose of this work is to investigate how phenomenologically successful constructions in the field of high energy physics can be embedded into a fundamental theory, and what we can learn from this procedure. In fact, the synergy of an effective and a fundamental approach might be very fruitful. On the one hand, it poses several theoretical challenges to potential candidates for a fundamental theory, which might be ruled out or restricted in their generality. On the other hand, this mutual interplay can inspire new experiments and observations or suggest correlations which are invisible from an effective point of view. Our starting point is that string theory is entitled to be a valid candidate for a fundamental theory by a series of properties such as the fact that it is a consistent, UV‐finite, anomaly‐free quantum theory and it describes, in appropriate limits, quantum field theory and general relativity, hence providing a unified description of the four known forces. Within string theory, we choose to work in the framework of type IIB flux compactifications where the issue of moduli stabilization can be successfully addressed. On the phenomenological side, we focus on particle physics and cosmology, and in particular on the MSSM and the mechanism of inflation, respectively. We construct and study two different models of inflation in string theory. These are models of brane inflation, i.e. models where the primordial exponential expansion of the universe is driven by a scalar field representing the position of a D3‐brane (a 3+1‐dimensional dynamical object) in a compact space. We show explicitly that, allowing for fine tuning, a prolonged stage of slow‐roll inflation can be achieved during which perturbations are generated in good agreement with the CMB data. In addition, we give an example of the fruitful synergy we mentioned above. One of our two models, namely inflation at the tip, might induce also DBI inflation which produces peculiar features in the spectrum of density perturbations that might be looked for using CMB data. On the particle physics side, we consider a model, the large volume scenario (LVS), which, among other things, provides a rationale for a low scale susy‐breaking. We perform some checks on the consistency of LVS as a string theory model. To this end, we formulate an educated guess for the form of string loop corrections. We then show that physical predictions such as the soft susy‐breaking terms are actually surprisingly robust against the inclusion of these corrections.

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Comparing brane inflation to WMAP

Cited by 130 publications

References 65 publications

Inflation and String Theory

Inflation and String Theory

Primordial Fluctuations and Non-Gaussianities in Multifield Dirac-Born-Infeld Inflation

Phenomenological aspects of type IIB flux compactifications

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