Barion Acoustic Oscillations

pic1:Final distribution of baryonic matter and its two peaks in density profile

pic2:Photon start to stream/the right panel/ but baryonic matter remain in its place.The graph shows the distribution of baryonic(blue line) matter and photons(red line)
Pictures from personal page of Prof.Martin White

In dark energy model approaches to solve the accelerating universe puzzle,in the first step we confront a problem.The problem is that we measure the effect of dark energy indirectly through its effect on expansion rate of universe H=H(z).

So generally there are three main cosmological tools/probes/ to address this problem.

1)Standard candle:Use to find the relation between luminosity distance and redshift.In process of finding this we need to integrate the inverse of Hubble parameter.

2)Standard rulers:Standard rulers are object that we know their measure in some epoch of universe history,so looking at them through a specific angle give us the opportunity to calculate the angular diameter distance, which like the luminosity distance,once more we are able to calculate the integral of expansion rate of universe.

3)Growth of structure,also permit us to put constraint on the expansion rate and consequently on Dark energy model./This probe is useful for determine the difference between modified gravity models with dark energy models./

Although the cosmological objects in general does not have a specific shape to use them as standard rules but in early universe we will found one.

Baryon acoustic oscillation is a standard ruler from the last scattering epoch.

What is the story?

In early universe when the density and the temperature of universe were high ,there was

a plasma of baryons, electrons, photons, neutrinos and Dark matter.

Baryons and electrons are coupled to photons through Thompson scattering /electromagnetism interaction/ and Dark matter is only coupled by gravitational interaction.Then the universe was expanding and becoming cool until the last scattering epoch /approximately 300000 years after big-bang/ when the photons decoupled from matter.This is because the energy of photons are not enough to ionized the hydrogen atoms, so electrons were bound by protons.

At this epoch the photons free stream to the universe but the baryonic matter distribution was maintain in the same radius of 100 Megaparsec.As the universe continues its expansion, photons

spread uniformly through universe, while there was a potential well constructed in the middle of the 100Mps shell which the baryonic matter is distributed in its shell uniformly .

This is the sound horizon.Now the gravitational potential cause the final configuration of Acoustic peaks as two peaks in mass profile, one in the middle and one in 100Mps.

This imprint remains in large scale structure.

If we compute 2-point correlation function in LSS,we will found the effect of sound horizon.

Baryon Oscillations are well used in order to:

1)For firm prediction of models with baryons

2)prediction of dark matter and baryonic matter density in CMB3)Using in order to determine 3)angular diameter size and put constraints on Dark Energy models.

Anyhow the ruler of BAO is inconveniently large.Probe of gigaparsec volume is required to mark a precision measurement of the BAO.

A nice internet pages on BAO:

http://astro.berkeley.edu/~mwhite/bao/

http://www.lsst.org/Science/BAO.shtml/

A course and a book.

In 2008-autumn there will be a course in cosmology in Perimeter Institute thought by

Niayesh Afshordi, and Mark Wyman, from Perimeter Institute.

The course is based upon the T. Padmanabhan great book

Cosmology and astrophysics through problems ,published by Cambridge University press.

Although the course presenters change the place of astrophysics and cosmology in title, but they

describe in their course description that:

"This course is aimed at advanced undergraduate and beginning graduate students, and is inspired by a book by the same title, written by Padmanabhan. Each session consists of solving one or two pre-determined problems, which is done by a randomly picked student. While the problems introduce various subjects in Astrophysics and Cosmology, they do not serve as replacement for standard courses in these subjects, and are rather aimed at educating students with hands-on analytic/numerical skills to attack new problems."

Anyhow I take this book from library too and try to keep my paste harmonised with the course

presented in Perimeter and Waterloo physics department.

For website of the course,click here.

SuperStructure Imprint & ISW

" An Imprint of Super-Structures on the Microwave Background due to the Integrated Sachs-Wolfe Effect"

is the name of article published by IFA Hawaii university physics department collegues Benjamin R. Granett, Mark C. Neyrinck, István Szapudi (IFA, Hawaii).

the lanel address is : arXiv:0805.3695

This physicist use Integrated Saches Wolfe effect first introduced by RainerKurt Saches and Arthur Michael Wolfe in 1968 to show the imprint of superclusters and supervoid on photons energy , coming from Last scattering surface.

This imprint which is detected by founding the correlation of CMB temprature fluctuations and galaxy number densities/from SDSS galaxy catalouge/ is a key observation for accelerating universe.

This imprint is in good agreement with the dark Energy assumption and accelerating universe.

Ok what is the story.

The story is easy to grasp.

If the photons travel to the gravitational potentials, they gain energy and have a blue shift in wavelenght in contrast ,if photons come up from potentiel well,they loss energy and has a reshift.Now the point is that ,if the universe is filled with dark matter in linear regime,there is no difference between the change of energy of photons when they are going in and coming outside a gravitational well/cluster/.BUT...

the interesting part of the story is when the universe is accelerating,so in meanwhile that photons live in the potential well,Dark energy -cosmological constant or ...causes the well to be shallowed and become less deep.So there is a difference between energy gain and loss for photons so we can see this imprint on CMB photons and that is the evidence of Accelerating universe.

Good and joyful part of the story is this that the ISW can be used as one of the probes of Dark energy because oit is measuring some quantity/fluctuation of tempreture and it's coreelation/in two different stage of universe.So it can tell us about the dynamic of this exotic dark component of the universe.

IFA team launch a website about the superclusters/over dense regions/, super voids as a tool to exploring the dark matter and dark energy in the universe also explaining the ISW effect and their work on last paper.The site is : http://ifa.hawaii.edu/cosmowave/supervoids/

Dark Energy models

As mentioned in the last blog: "There are many models trying to describe the Accelerating universe problem", the most popular ones are listed as below.

1)Vacuum Energy-Cosmological constant

From Quantum field theory we know that we can relate harmonic oscillator to the vacuum state of QFT(Quantum field Theory)and as we know from the classical mechanics,the ground state of harmonic oscillator has non-zero energy which can contribute to the Dark energy.

In the other way we can easily interpret the energy momentum of vacuum energy as an cosmological constant/which Einstein first proposed before Hubble's discovery to get the static universe and later call it his life's biggest blunder/.

2)Dark Energy models

a)Quintessence

b)k-essence

c)phantom-ghost like fields

d)Pseudo-Nambo-Goldstone bosons

e)Oscillating dark energy models

Dark energy models containing all the subdivisions mention about,are physical models.All proposed a new kind of constitute of universe that has ridiculous equation of state.Usually this exotic entity is related to a scalar field.

3)Failure of General Relativity

a)Gravitation action is a general function of a Ricci scalar , scalars from Ricci and Riemann tensor

b)Scalar-Vector-tensor theories

d)Brane world cosmologies

this models discuss and propose that maybe we do not understand the gravity well and we should change the Einstein-Hilbert action to more general one.

The Brane world cosmologies suggest that in stead of 4D we live in a brane embedded in 5 Dimensions,in this case the gravity leakage to the 5-dimension in contrast to the matter and other force fields that are constrained to live in 4D.the result of this causes modification to the gravity understanded in 4D and causes the accelerating universe.

4)Chamelon models

This models suggest any exotic component of universe with equation of state that in early times behave like dark matter and in late universe is playing the role of dark energy

5)Dark energy,Dark matter interacting models

6)Failure of FRW-assumption.

In this inhomogeneous models the back reaction of structures cause to alter the distances we measure from standard candle SNIa,,and the dark energy is just a miscalculation.

7)Holographic dark energy

In this models our 4d manifold is a hologram of higher dimensional world

8)String theory landscape

In the framework of string theory the cosmological constant solution for accelerating universe is once again proposed and more, the problems of fine tunning and cosmic coincidence is answered by the landscape interpretation.

9)Quantum Geometry

That the space and time is also quantized and are manifestation of a new field.

10)Anthropic principle models

I will blog about it later...

There are other models too!!It seems that really we do not understand the physics of accelerating universe so so much models come to existing.

Let do more physics to found out the mystery.

Review articles in Accelerating universe

Since the discovery of Accelerating universe many theoretical models were introduced in order to describe the cause of this acceleration.
The models generally, are divided into two main parts.
1)Geometrical ones & 2)Physical ones.
Geometrical models assert that we do not understand the physics of gravity-(geometry)/because of GR/, in long ranges and small curvatures.So we must change the context of general relativity and then consequently we will be able to solve the problem of Accelerating universe ./This models are called generally Modified gravity models/
The other part are standing the physicists that claim the right theory is the physical ones.
They introduce new physical quantities like scalar field (Dark energy models-Quintessence models) with new thermodynamical properties / w<-1/3(Equation of state)/ to describe this problem.
Anyhow many there are many other approaches proposed in last decade that lately, I will post a blog listing the most fav. ones.
But what is the good part of the story is that there are many review papers
"God bless them " , that we can grasp the late happenings in the field of accelerating universe through studying them.
Let me name some :

1) Joshua Frieman (Chicago/Fermilab), Michael Turner (Chicago), Dragan Huterer(Michigan)/2008/
2)Eric V. Linder /2008/
3))Eric V. Linder/2007/
4) T. Padmanabhan /2007/
5)Edmund J. Copeland, M. Sami, Shinji Tsujikawa/2006/
6)Varun Sahni , Alexei Starobinsky/2006/
7)Rachel Bean, Sean Carroll, Mark Trodden /2005/
8) P. J. E. Peebles, Bharat Ratra /2002/
9)Dragan Huterer, Michael S. Turner /2001/
10)Sean M. Carroll /2000/

Hope to enjoy them.

Accelerating Universe

It is just a decade from revolutionary foundings of two SuperNova Suravy teams:

1)Supernova Cosmology Project , at the Lawrence Berkeley National Laboratory and the 2)High-z Supernova Search Team

/Riess(1998) and Perlmutter (1999)/ .They cliam that the SNIa ,which asserted to be standard candels are dimmer than that they seem to be in Standard CDM -model.

So...

What does it mean?

It means that if SNIa are really standard candels, we must wait to something revolutionary in cosmology.

This is because that in the context (becareful about the term used here,it means that we accept the GR and big-bang model ) of general relativity(GR)and Big-Bang model and cosmological principle(Homogenious,Isotropic universe) , we confront with two choises in order to describe the supernova observation:

1)The universe is open- K>0 /k is curvature/

or

2)Universe expansion is accelerating - q<0>

Now day with precise measurement in cosmology like WMAP-5 years result

,we know that curvature of our universe is nearly flat and from Large scale structure measurement the 30% of our known universe is Dark-ordinary Matter.

So ...

Universe is in phase of accelerated expansion and an unknown component of universe which contain 70% of it that may cause this(if we accept GR and cosmological principle) is Dark Energy.

"What is this unknown Dark Energy ,what causes of this acceleration?"

this is one of the greatest questions of physics for new millennium.

Hello TiYezerk

Hello TiYezerk

This is a new blog, specialized in Cosmology, and also other related branches of physics written by Shant Baghram, a Ph.D. Student of physics in Sharif university in Tehran.

The aim of blog first of all is self training to write down about more specialized topics in cosmology in couple of paragraphs, also to keep myself updated to the progress in this fantastic science area .

The start point of this blog is August 25-2008 in last days of my first Ph.D. studying year. Let see where does the train of cosmology go!!!

The name of blog is taken from the Armenian world for "Universe" which is Tiyezerk

Ti : great, big.

Yezerk: boundry .

It seems that the Armenian word of TiYezerk is somehow contains a topological point of view!,the word! believe that the universe has a boundary unless it is great.

Let me keep blogging!

Hello TiYezerk