arXiv subjects

Mark G. Jackson

Publications and source records attributed to Mark G. Jackson.

At least 19 recordsLinked to original sources

arXiv2013

A Consistency Relation for Single-Field Inflation with Power Spectrum Oscillations

We derive a theoretical upper bound on the oscillation frequency in the scalar perturbation power spectrum of single-field inflation. Oscillations are most naturally produced by modified vacua with varying phase. When this phase changes rapidly, it induces strong interactions between the scalar fluctuations. If the interactions are sufficiently strong the theory cannot be evaluated using perturbation theory, hence imposing a limit on the oscillation frequency. This complements the bound found by Weinberg governing the validity of effective field theory. The generalized consistency relation also allows one to use squeezed configurations of higher-point correlations to place constraints on the power spectrum oscillations.

hep-th↗

arXiv2013

Angular Correlation Functions for Models with Logarithmic Oscillations

There exist several theoretical motivations for primordial correlation functions (such as the power spectrum) to contain oscillations as a logarithmic function of comoving momentum k. While these features are commonly searched for in k-space, an alternative is to use angular space; that is, search for correlations between the directional vectors of observation. We develop tools to efficiently compute the angular correlations based on a stationary phase approximation and examine several example oscillations in the primordial power spectrum, bispectrum, and trispectrum. We find that logarithmically-periodic oscillations are essentially featureless and therefore difficult to detect using the standard correlator, though others might be feasible.

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arXiv2013

Model-Independent Signatures of New Physics in Slow-Roll Inflation

We compute the universal generic corrections to the power spectrum in slow-roll inflation due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the "in-in" formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. The density power spectrum is universally modified at leading order in $H/M$, the ratio of the scale of inflation to the scale of new physics; the tensor power spectrum receives only subleading corrections. In doing so, we show how to make sense of a physical momentum-cut-off in loop integrals despite dynamical redshifts, and how the result can be captured in a combined effective action/effective density matrix, where the latter contains non-adiabatic terms which modify the boundary conditions.

hep-th↗

arXiv2013

Model-Independent Signatures of New Physics in non-Gaussianity

We compute the model-independent contributions to the primordial bispectrum and trispectrum in de Sitter space due to high-energy physics. We do this by coupling a light inflaton to an auxiliary heavy field, and then evaluating correlation functions in the Schwinger-Keldysh "in-in" formalism. The high-energy physics produces corrections parametrized by $H/M$ where $H$ is the scale of inflation and $M$ is the mass of the heavy field. The bispectrum peaks near the elongated shape, but otherwise contains no features. The trispectrum receives no corrections at order $H/M$.

hep-th↗

arXiv2012

Integrating out Heavy Fields in Inflation

I present the procedure for integrating out quantum fields whose mass M is well above the Hubble scale H in de Sitter space. The effective interaction and density matrix are explicitly computed for a simple example and are found to be of order H/M, are nonlocally distributed in time and contain a highly oscillatory phase. This radical departure from the static space-time result demonstrates that these new tools are necessary for constructing effective inflationary potentials. The effective coupling naturally forms a perturbative series in the relative energy transferred ΔE/M, whose coefficients can then be compared to observation.

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arXiv2011

Model Independent Signatures of New Physics in the Inflationary Power Spectrum

We compute the universal generic corrections to the inflationary power spectrum due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the "in-in" formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. We find that the power spectrum is universally modified at order H/M, where H is the scale of inflation. This is qualitatively different from the universal corrections in time-independent backgrounds, and it suggests that such effects may be present in upcoming cosmological observations.

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arXiv2009

Bispectrum signatures of a modified vacuum in single field inflation with a small speed of sound

Deviations from the Bunch-Davies vacuum during an inflationary period can leave a testable imprint on the higher-order correlations of the CMB and large scale structures in the Universe. The effect is particularly pronounced if the statistical non-Gaussianity is inherently large, such as in models of inflation with a small speed of sound, e.g. DBI. First reviewing the motivations for a modified vacuum, we calculate the non-Gaussianity for a general action with a small speed of sound. The shape of its bispectrum is found to most resemble the 'orthogonal' or 'local' templates depending on the phase of the Bogolyubov parameter. In particular, for DBI models of inflation the bispectrum can have a profound 'local' template feature, in contrast to previous results. Determining the projection into the observational templates allows us to derive constraints on the absolute value of the Bogolyubov parameter. In the small sound speed limit, the derived constraints are generally stronger than the existing constraint derived from the power spectrum. The bound on the absolute value of the Bogolyubov parameter ranges from the 10^-6 to the 10^-3 level for H/Λ_c = 10^-3, depending on the specific details of the model, the sound speed and the phase of the Bogolyubov parameter.

hep-th↗

arXiv2009

Holographic Geometry and Noise in Matrix Theory

Using Matrix Theory as a concrete example of a fundamental holographic theory, we show that the emergent macroscopic spacetime displays a new macroscopic quantum structure, holographic geometry, and a new observable phenomenon, holographic noise, with phenomenology similar to that previously derived on the basis of a quasi-monochromatic wave theory. Traces of matrix operators on a light sheet with a compact dimension of size $R$ are interpreted as transverse position operators for macroscopic bodies. An effective quantum wave equation for spacetime is derived from the Matrix Hamiltonian. Its solutions display eigenmodes that connect longitudinal separation and transverse position operators on macroscopic scales. Measurements of transverse relative positions of macroscopically separated bodies, such as signals in Michelson interferometers, are shown to display holographic nonlocality, indeterminacy and noise, whose properties can be predicted with no parameters except $R$. Similar results are derived using a detailed scattering calculation of the matrix wavefunction. Current experimental technology will allow a definitive and precise test or validation of this interpretation of holographic fundamental theories. In the latter case, they will yield a direct measurement of $R$ independent of the gravitational definition of the Planck length, and a direct measurement of the total number of degrees of freedom.

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arXiv2009

Constraining Running Non-Gaussianity

The primordial non-Gaussian parameter fNL has been shown to be scale-dependent in several models of inflation with a variable speed of sound. Starting from a simple ansatz for a scale-dependent amplitude of the primordial curvature bispectrum for two common phenomenological models of primordial non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the temperature and polarization of the Cosmic Microwave Background (CMB) radiation and derive the expected constraints on the parameter nNG that quantifies the running of fNL(k) for current and future CMB missions such as WMAP, Planck and CMBPol. We find that CMB information alone, in the event of a significant detection of the non-Gaussian component, corresponding to fNL = 50 for the local model and fNL = 100 for the equilateral model of non-Gaussianity, is able to determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG = 0.3, respectively, for the Planck mission. In addition, we consider a Fisher matrix analysis of the galaxy power spectrum to determine the expected constraints on the running parameter nNG for the local model and of the galaxy bispectrum for the equilateral model from future photometric and spectroscopic surveys. We find that, in both cases, large-scale structure observations should achieve results comparable to or even better than those from the CMB, while showing some complementarity due to the different distribution of the non-Gaussian signal over the relevant range of scales. Finally, we compare our findings to the predictions on the amplitude and running of non-Gaussianity of DBI inflation, showing how the constraints on a scale-dependent fNL(k) translate into constraints on the parameter space of the theory.

astro-ph.CO↗

arXiv2009

CMBPol Mission Concept Study: Probing Inflation with CMB Polarization

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B-mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super-Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale-dependence and non-Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.

astro-ph↗

arXiv2009

Gravitational Wave Bursts from Cosmic Superstring Reconnections

We compute the gravitational waveform produced by cosmic superstring reconnections. This is done by first constructing the superstring reconnection trajectory, which closely resembles that of classical, instantaneous reconnection but with the singularities smoothed out due to the string path integral. We then evaluate the graviton vertex operator in this background to obtain the burst amplitude. The result is compared to the detection threshold for current and future gravitational wave detectors, finding that neither bursts nor the stochastic background would be detectable by Advanced LIGO. This disappointing but anticipated conclusion holds even for the most optimistic values of the reconnection probability and loop sizes.

hep-th↗

arXiv2008

Spin-Statistics Violations in Superstring Theory

I describe how superstring theory may violate spin-statistics in an experimentally observable manner. Reviewing the basics of superstring interactions and how to utilize these to produce a statistical phase, I then apply these ideas to two specific examples. The first is the case of heterotic worldsheet linkings, whereby one small closed string momentarily enlarges sufficiently to pass over another, producing such a statistical phase. The second is the braneworld model with noncommutative geometry, whereby matter composed of open strings may couple to a background in which spacetime coordinates do not commute, modifying the field (anti)commutator algebra. I conclude with ways to sharpen and experimentally test these exciting avenues to possibly verify superstring theory.

hep-th↗

arXiv2008

CMBPol Mission Concept Study: A Mission to Map our Origins

Quantum mechanical metric fluctuations during an early inflationary phase of the universe leave a characteristic imprint in the polarization of the cosmic microwave background (CMB). The amplitude of this signal depends on the energy scale at which inflation occurred. Detailed observations by a dedicated satellite mission (CMBPol) therefore provide information about energy scales as high as $10^{15}$ GeV, twelve orders of magnitude greater than the highest energies accessible to particle accelerators, and probe the earliest moments in the history of the universe. This summary provides an overview of a set of studies exploring the scientific payoff of CMBPol in diverse areas of modern cosmology, such as the physics of inflation, gravitational lensing and cosmic reionization, as well as foreground science and removal .

astro-ph↗

arXiv2008

Spin-Statistics Violations from Heterotic String Worldsheet Instantons

In this paper we consider the role that worldsheet instantons in the heterotic string could play in spin-statistics violations. Such violations are nonperturbative in the string tension and so would not appear in the spacetime effective action, producing a unique signature of string theory and the details of compactification. By performing a Bogomol'nyi transformation it is shown that there are no instanton solutions in the simplest model proposed by Harvey and Liu, but it is conjectured that more sophisticated models may yield solutions. If such instantons do exist, their effect might be measured by upcoming experiments.

hep-th↗

arXiv2008

A New Spin on Quantum Gravity

We suggest that the (small but nonvanishing) cosmological constant, and the holographic properties of gravitational entropy, may both reflect unconventional quantum spin-statistics at a fundamental level. This conjecture is motivated by the nonlocality of quantum gravity and the fact that spin is an inherent property of spacetime. As an illustration we consider the `quon' model which interpolates between fermi and bose statistics, and show that this can naturally lead to an arbitrarily small cosmological constant. In addition to laboratory tests, we briefly discuss the possible observable imprint on cosmological fluctuations from inflation.

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arXiv2007

Interactions of Cosmic Superstrings

We develop methods by which cosmic superstring interactions can be studied in detail. These include the reconnection probability and emission of radiation such as gravitons or small string loops. Loop corrections to these are discussed, as well as relationships to $(p,q)$-strings. These tools should allow a phenomenological study of string models in anticipation of upcoming experiments sensitive to cosmic string radiation.

hep-th↗

arXiv2007

A Note on Cosmic (p,q,r) Strings

The spectrum of $(p,q)$ bound states of F- and D-strings has a distinctive square-root tension formula that is hoped to be a hallmark of fundamental cosmic strings. We point out that the Bogomol'nyi-Prasad-Sommerfield (BPS) bound for vortices in ${\cal N}=2$ supersymmetric Abelian-Higgs models also takes the square-root form. In contrast to string theory, the most general supersymmetric field theoretic model allows for $(p,q,r)$ strings, with three classes of strings rather than two. Unfortunately, we find that there do not exist BPS solutions except in the trivial case. The issue of whether there exist non-BPS solutions which may closely resemble the square-root form is left as an open question.

hep-th↗

arXiv2006

Cosmic Superstring Scattering in Backgrounds

We generalize the calculation of cosmic superstring reconnection probability to non-trivial backgrounds. This is done by modeling cosmic strings as wound tachyon modes in the 0B theory, and the spacetime effective action is then used to couple this to background fields. Simple examples are given including trivial and warped compactifications. Generalization to $(p,q)$ strings is discussed.

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