Conceptual issues in inflation
Download
1 / 48

Conceptual Issues in Inflation - PowerPoint PPT Presentation


  • 151 Views
  • Uploaded on

Conceptual Issues in Inflation. New Inflation. 1981 - 1982. V. Chaotic Inflation. 1983. Eternal Inflation. Hybrid Inflation. 1991, 1994. WMAP5 + Acbar + Boomerang + CBI. Tensor modes:. Kallosh, A.L. 2007.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Conceptual Issues in Inflation' - cayla


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

New Inflation

1981 - 1982

V


Chaotic inflation
Chaotic Inflation

1983

Eternal Inflation


Hybrid Inflation

1991, 1994



Tensor modes:

Kallosh, A.L. 2007

It does make sense to look for tensor modes even if none are found at the level r ~ 0.1 (Planck)


Blue lines – chaotic inflation with the simplest spontaneous symmetry breaking potential for N = 50 and N = 60


Destri, de Vega, Sanchez, 2007 spontaneous symmetry breaking potential for N = 50 and N = 60

Possible values of r and ns for chaotic inflation with a potential including terms

for N = 50. The color-filled areas correspond to various confidence

levels according to the WMAP3 and SDSS data.

Almost all points in this area can be fit by chaotic inflation including terms


What is f nl
What is f spontaneous symmetry breaking potential for N = 50 and N = 60NL?

Komatsu 2008:

k2

k1

k3

fNL = the amplitude of three-point function

also known asthe “bispectrum,” B(k1,k2,k3), which is

<Φ(k1)Φ(k2)Φ(k3)>=fNL(2π)3δ3(k1+k2+k3)b(k1,k2,k3)

Φ(k) is the Fourier transform of the curvature perturbation, and b(k1,k2,k3) is a model-dependent function that defines the shape of triangles predicted by various models.

11


Why bispectrum
Why Bispectrum? spontaneous symmetry breaking potential for N = 50 and N = 60

  • The bispectrum vanishesfor Gaussian random fluctuations.

  • Any non-zero detection of the bispectrum indicates the presence of (some kind of) non-Gaussianity.

  • A very sensitive tool for finding non-Gaussianity.

12


Two f nl s
Two f spontaneous symmetry breaking potential for N = 50 and N = 60NL’s

Komatsu & Spergel (2001); Babich, Creminelli & Zaldarriaga (2004)

  • Depending upon the shape of triangles, one can define various fNL’s:

  • “Local” form

    • which generates non-Gaussianity locally (i.e., at the same location) via Φ(x)=Φgaus(x)+fNLlocal[Φgaus(x)]2

  • “Equilateral” form

    • which generates non-Gaussianity in a different way (e.g., k-inflation, DBI inflation)

  • Earlier work on the local form:

    Salopek&Bond (1990); Gangui et al. (1994); Verde et al. (2000); Wang&Kamionkowski (2000)

    13


    Can we have large nongaussianity

    A.L., Kofman 1985-1987, A.L., Mukhanov, 1996, spontaneous symmetry breaking potential for N = 50 and N = 60

    Lyth, Wands, Ungarelli, 2002

    Lyth, Wands, Sasaki and collaborators - many papers up to 2008

    V

    Can we have large nongaussianity ?

    V

    Curvaton

    Inflaton

    Isocurvature perturbationsadiabatic perturbations

    is determined by quantum fluctuations, so the amplitude of perturbations is different in different places


    Spatial Distribution of the Curvaton Field spontaneous symmetry breaking potential for N = 50 and N = 60

    0


    The Curvaton Web and Nongaussianity spontaneous symmetry breaking potential for N = 50 and N = 60

    Usually we assume that the amplitude of inflationary perturbations is constant, H~ 10-5 everywhere. However, in the curvaton scenario Hcan be different in different parts of the universe. This is a clear sign of nongaussianity.

    A.L., Mukhanov, astro-ph/0511736

    The Curvaton Web

    H


    Alternatives ekpyrotic cyclic scenario
    Alternatives? spontaneous symmetry breaking potential for N = 50 and N = 60Ekpyrotic/cyclic scenario

    Original version (Khoury, Ovrut, Steinhardt and Turok 2001) did not work (no explanation of the large size, mass and entropy; the homogeneity problem even worse than in the standard Big Bang, Big Crunch instead of the Big Bang, etc.).

    It was replaced by cyclic scenario (Steinhardt and Turok 2002) which is based on a set of conjectures about what happens when the universe goes through the singularity and re-emerges.

    Despite many optimistic announcements, the singularity problem in 4-dimensional space-time and several other problems of the cyclic scenario remain unsolved.


    Recent developments spontaneous symmetry breaking potential for N = 50 and N = 60: “New ekpyrotic scenario”

    Creminelly and Senatore, 2007, Buchbinder, Khoury, Ovrut 2007

    Problems: violation of the null energy condition, absence of the ultraviolet completion, difficulty to embed it in string theory,violation of the second law of thermodynamics,problems with black hole physics.

    The main problem: this theory contains terms with higher derivatives, which lead to new ekpyrotic ghosts, particles with negative energy. As a result, the vacuum state of the new ekpyrotic scenario suffers from a catastrophic vacuum instability.

    Kallosh, Kang, Linde and Mukhanov, arXiv:0712.2040


    The New Ekpyrotic Ghosts spontaneous symmetry breaking potential for N = 50 and N = 60

    New Ekpyrotic Lagrangian:

    Dispersion relation:

    Two classes of solutions, for small P,X:

    ,

    Hamiltonian describes normal particles with positive energy + 1 and ekpyrotic ghosts with negative energy - 2


    Vacuum in the new ekpyrotic scenario instantly decays due to emission of pairs of ghosts and normal particles.

    Cline, Jeon and Moore, 2003


    Why higher derivatives? Can we introduce a UV cutoff? emission of pairs of ghosts and normal particles.

    Bouncing from the singularity requires violation of the null energy condition, which in turn requires

    Dispersion relation for perturbations of the scalar field:

    The last term appears because of the higher derivatives. If one makes this term vanish at large k, then in the regime one has a catastrophic vacuum instability, with perturbations growing as

    Of course, one can simply assume the existence of a UV cutoff at energies higher than the ghost mass, but this would be an inconsistent theory, until the physical origin of the cutoff is found. Moreover, in a theory with a UV cutoff, why would one care about the cosmological singularity? At this level, the singularity problem could be solved many decades ago (no high energy modes no space-time singularity).


    “But ghosts have disastrous consequences for the viability of the theory. In order to regulate the rate of vacuum decay one must invoke explicit Lorentz breaking at some low scale. In any case there is no sense in which a theory with ghosts can be thought as an effective theory, since the ghost instability is present all the way to the UV cut-off of the theory.”

    Buchbinder, Khoury, Ovrut 2007


    Example: of the theory. In order to regulate the rate of vacuum decay one must invoke explicit Lorentz breaking at some low scale. In any case there is no sense in which a theory with ghosts can be thought as an effective theory, since the ghost instability is present all the way to the UV cut-off of the theory.”

    Can be obtained by integration with respect to of the theory with ghosts

    By adding some other terms and integrating out the field one can reduce this theory to the ghost-free theory.

    Can we save this theory?

    Creminelli, Nicolis, Papucci and Trincherini, 2005

    But this can be done only for a = + 1, whereas in the new ekpyrotic scenario a = - 1

    Kallosh, Kang, Linde and Mukhanov, arXiv:0712.2040


    Even if it is possible to improve the new ekpyrotic scenario (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    We are unaware of any examples of the ghost-free theories where the null energy condition is violated.


    A toy model of sugra inflation
    A toy model of SUGRA inflation: (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    Holman, Ramond, Ross, 1984

    Superpotential:

    Kahler potential:

    Inflation occurs for0 = 1

    Requires fine-tuning, but it is simple, and it works


    A toy model of string inflation
    A toy model of string inflation: (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    A.L., Westphal, 2007

    Superpotential:

    Kahler potential:

    Volume modulus inflation

    Requires fine-tuning, but works without any need to study complicated brane dynamics


    String Cosmology and the Gravitino Mass (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    Kallosh, A.L. 2004

    The height of the KKLT barrier is smaller than |VAdS| =m23/2. The inflationary potential Vinfl cannot be much higher than the height of the barrier. Inflationary Hubble constant is given by H2 = Vinfl/3 < m23/2.

    uplifting

    Modification of V at large H

    VAdS

    Constraint on the Hubble constant in this class of models:

    H < m3/2


    Can we avoid these conclusions
    Can we avoid these conclusions? (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    Recent model of chaotic inflation is string theory (Silverstein and Westphal, 2007) also require .

    H < m3/2

    In more complicated theories one can have . But this

    requires fine-tuning (Kallosh, A.L. 2004, Badziak, Olechowski, 2007)

    In models with large volume of compactification (Quevedo et al) the situation is even more dangerous:

    It is possible to solve this problem, but it is rather nontrivial.

    Conlon, Kallosh, A.L., Quevedo, in preparation

    Remember that we are suffering from the light gravitino and the cosmological moduli problem for the last 25 years.

    The price for the SUSY solution of the hierarchy problem is high, and it is growing. Split supersymmetry? We are waiting for LHC...


    Landscape of eternal inflation (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.


    What is so special about our world? (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    Problem:Eternal inflation creates infinitely many different parts of the universe, so we must compare infinities


    Two different approaches: (which was never demonstrated), then it will be necessary to check whether the null energy condition is still violated in the improved theory despite the postulated absence of ghosts. Indeed, if the correction will also correct the null energy condition, then the bounce will become impossible.

    Study events at a given point, ignoring growth of volume, or, equivalently, calculating volume in comoving coordinates

    Starobinsky 1986, Garriga, Vilenkin 1998, Bousso 2006, A.L. 2006

    No problems with infinities, but the results depend on initial conditions. It is not clear whether these methods are appropriate for description of eternal inflation, where the exponential growth of volume is crucial.

    2.Take into account growth of volume

    A.L. 1986; A.L., D.Linde, Mezhlumian, Garcia-Bellido 1994; Garriga, Schwarz-Perlov, Vilenkin, Winitzki 2005; A.L. 2007

    No dependence on initial conditions, but we are still learning how to do it properly.


    Let us discuss non eternal inflation to learn about the measure
    Let us discuss non-eternal inflation to learn about the measure

    The universe is divided into two parts, one inflates for a long time, one does it for a short time. Both parts later collapse.


    More observers live in the inflationary (part of the) universe because there are more stars and galaxies there


    Comoving probability measure does not distinguish small and big universes and misses most of the stars


    One can use the volume weighted measure parametrized by time t proportional to the scale factor a. In this case the two parts of the universe grow at the same rate, but the non-inflationary one stops growing and collapses while the big one continues to grow. Thus the comparison of the volumes at equal times fails.

    Scale factor cutoff, t = a


    When we make a cut, in the beginning inflation does not provide us any benefit: No gain in volume.

    This could suggest that the growth of volume during inflation does not have any anthropic significance


    But when we move the cut-off higher, the comparison between the two parts of the universe becomes impossible. The small part of the universe dies early, whereas the inflationary universe continues to grow.

    When we remove the cut-off, we find the usual result: Most of the observers live in the universe produced by inflation.


    V the two parts of the universe becomes impossible. The small part of the universe dies early, whereas the inflationary universe continues to grow.

    Boltzmann Brains are coming!!!

    BB3

    BB1

    Hopefully, normal brains are created even faster, due to eternal inflation


    Consider first the scale factor cutoff, t = a.

    If the dominant vacuum cannot produce Boltzmann brains, and our vacuum decays before BBs are produced we will not have any problems with them.

    Freivigel, Bousso et al, in preparation

    De Simone, Guth, Linde, Noorbala, Salem,Vilenkin, in preparation

    Can we realize this possibility? Recall that

    Ceresole, Dall’Agata, Giryavets, Kallosh, A.L., 2006

    The long-living vacuum tend to be the ones with an (almost) unbroken supersymmetry, . But people like us cannot live in a supersymmetric universe.

    In other words, Boltzmann brains born in the stable vacua tend to be brain-dead.

    More on this – in the talks by Vilenkin and Freivogel



    Time can be measured in the number of oscillations ( ) or in the number of e-foldings of inflation ( ). The universe expands as

    is the growth of volume during inflation

    Unfortunately, the result depends on the time parametrization.


    t ) or in the number of e-foldings of inflation ( ). The universe expands as 21

    t45

    t = 0

    We should compare the “trees of bubbles” not at the time when the trees were seeded, but at the time when the bubbles appear


    A possible solution of this problem: ) or in the number of e-foldings of inflation ( ). The universe expands as

    If we want to compare apples to apples, instead of the trunks of the trees, we need to reset the time to the moment when the stationary regime of exponential growth begins. In this case we obtain the gauge-invariant result

    As expected, the probability is proportional to the rate of tunneling and to the growth of volume during inflation.

    A.L., arXiv:0705.1160


    In general, according to the stationary measure, if we have two possible outcomes of a process starting at t = 0

    where ti is the time when the stationarity regime for the corresponding process is established.

    The more probable is the trajectory, the longer it takes to reach stationarity, the better. For example, the ratio of the probabilities for different temperatures in the domains of the same type is

    Slight preference for lower temperatures, no youngness paradox.

    A.L. 2007

    Moreover, we believe that the youngness paradox does not appear even if one takes into account inhomogeneities of temperature.

    A.L., Vanchurin, Winitzki, in preparation


    These results agree with the expectation that the probability to be born in a part of the universe which experienced inflation can be very large, because of the exponential growth of volume during the slow-roll inflation.


    No Boltzmann Brainer probability to be born in a part of the universe which experienced inflation can be very large, because of the exponential growth of volume during the

    A.L., Vanchurin, Winitzki, in preparation

    Stationary measure does not lead to the Boltzmann brain problem

    The ratio of BBs to OOs is proportional to the ratios of the volumes of the universe when the stationarity is reached for BBs and OOs (which rewards OOs), multiplied by the extremely small probability of the BB production in the vacuum.

    Example: In the no-delay situation (A.L. 2006)

    In a more general and realistic situation, with the time delay, taking into account thermal fluctuations, the result is very similar, no BBs:


    Conclusions: probability to be born in a part of the universe which experienced inflation can be very large, because of the exponential growth of volume during the

    There is an ongoing progress in implementing inflation in supergravity and string theory.

    As on now, we are unaware of any non-inflationary alternatives which are verifiably consistent.

    CMB can help us to test string theory. If inflationary tensor modes are discovered, we may need to develop phenomenological models with superheavy gravitino.

    Looking forward, we must either propose something better than inflation and string theory in its present form, or learn how to make probabilistic predictions based on eternal inflation and the string landscape scenario. Several promising probability measures were proposed, including the stationary measure.


    Here our conclusions differ from those of probability to be born in a part of the universe which experienced inflation can be very large, because of the exponential growth of volume during the

    Bousso, Freivogel and Yang, 2007

    They confirmed that in the absence of perturbations of temperature T, the probability distribution to be born in the universe with a given T depends on T smoothly, and does not suffer from the youngness problem. However, when they took into account perturbations of temperature, they found, in the approximation which they proposed, that

    Here 1010 stays for the inverse square of the amplitude of perturbations of temperature induced by inflationary perturbations. The first term is much greater, which leads to “oldness” paradox: Small T are exponentially better.

    Note, however, that if one takes the limit when the amplitude of perturbations vanishes, the coefficient in front of the second term in the exponent blows up, and the probability distribution becomes singular, concentrated at T = 3.3 K.

    This contradicts their own result that in the absence of perturbations of temperature, the probability distribution is smooth.


    A toy landscape model probability to be born in a part of the universe which experienced inflation can be very large, because of the exponential growth of volume during the

    Mahdiyar Noorbala, A.L. 2008


    As an example, consider Bousso measure, assuming first that Boltzmann brains can be born in all vacua

    However, “stable vacua” are not really stable. In a typical situation in stringy landscape one expects their decay rate

    Ceresole, Dall’Agata, Giryavets, Kallosh, A.L., 2006

    Such vacua could be BB safe. If there are other vacua, with a small SUSY breaking, they may be stable but it is dangerous only if


    ad