Regularizing cosmological singularities by varying physical constants
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Regularizing cosmological singularities by varying physical constants. Konrad Marosek Szczecin Cosmology Group , University of Szczecin, Poland. 49th Winter School of Theoretical P hysics Lądek-Zdrój, Poland, February 10-16, 2013. 1. Introduction.

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Regularizing cosmological singularities by varying physical constants

Regularizing cosmological singularities by varying physical constants.

Konrad Marosek

Szczecin CosmologyGroup, University of Szczecin, Poland.

49th Winter School of TheoreticalPhysics

Lądek-Zdrój, Poland, February 10-16, 2013


1 introduction

1. Introduction

The idea of variation of physicalconstantshasbeenestablishedwidelyinphysicsboththeoretically and experimentally. Fromthetheoreticalsidetheearlyideas of Weyl and Eddingtonwere most successfullyfollowed by Dirac’sLargeNumberHypothesisfromwhichit was concludedthatthegravitationalconstantshouldchangein time as . Thisled to thescalar-tensorgravitytheorydeveloped by Brans and Dickewhofollowedtheideas of Jordan.Theseideaswerefurtherembeddedintosuperstringtheoriesinwhichthecouplingconstant of gravitybecamerunningduringtheevolution of theearlyuniverse (Polchinski 1996).


Introduction ctd

Introduction (ctd.)

The most popular theorieswhichadmitphysicalconstantsvariationarethevaryingspeed of lighttheoriesand varyingα alpha (finestructure) theories (Barrow et al. 1999). Ithasbeenshownthatboth of thesetheoriesallowthesolution of the standard cosmologicalproblemssuch as thehorizonproblem,flatnessproblem,and the−problem. Here, we will applythesetheories to solveyetanother problem - thesingularityproblem.


Introduction ctd1

Introduction (ctd.)

  • Primordialnucleosynthesis(Accetta et al. 1990):

  • Helioseismology (Guenther et al.1998):

  • Lunar laser ranging(LLR) (Williams et al. 1996):


Introduction ctd2

Introduction (ctd.)

  • Oklophenomenon (Shlyakhter 1976,Petrov et al. 2006):

  • Meteorite dating (long-lived beta decays) (Olive et al. 2003):

  • Quasarabsorption spectra withredshifts 2.33 < z < 3.08 (Murphy et al. 2001):

    Where


2 varying constants models

2.VARYING CONSTANTS MODELS

Einstein-Friedman equations with varying fundamental constans can be expressed as:

and the energy-momentum conservation law is:


Varying constants models

VARYING CONSTANTS MODELS

In contrast to many references dealing with non-standard singularities (e.g. sudden future singularities), which consider the scale factor:

Where , , , , are constants.

We propose a new form of the scale factor:

Where , , , are constants.


Varying constants models1

VARYING CONSTANTS MODELS

The first and second derivatives of the scale factor are as follows:


Varying constants models2

VARYING CONSTANTS MODELS

Einstein-Friedman equations for zero curvature (k=0) models now are expressed by:


Varying constants models3

VARYING CONSTANTS MODELS

For we dealwith Big-Bang singularity

Type 0 – Big-Bang (BB): , , , at .

For we have a Big-Ripsingularity

Type I - Big-Rip (BR): , , , at .

For we have a SuddenFuturesingularity

Type II - SuddenFutureSingularity(SFS): ,

, , at .

For we haveFiniteScalarFactorsingularity

Type III - FiniteScalarFactor(FSF): , ,

, at .


Regularizing cosmological singularities by varying physical constants

VARYING CONSTANTS MODELS

The plots of the scale factor , the energy density ,

and the pressure :

for theparameters , and , whichdescribe

a suddenfuturesingularity(SFS)


Regularizing cosmological singularities by varying physical constants

VARYING CONSTANTS MODELS

The plots of the scale factor , the energy density ,

and the pressure :

for theparameters , and , whichdescribe

a finitescalefactorsingularity(SFS)


Varying constants models4

VARYING CONSTANTS MODELS

We cansplitourscalefactorinthefollowingway:

where:

and

In a specialcase we get a standard big-bangscalefactorwith


Varying constants models5

VARYING CONSTANTS MODELS

Is possible to write down an equation of state inthe form of a barotropic perfect fluid as:

whereas in the standard notation.

The standard big-bang are decelerating for ,

and accelerating for .

Thepressureispositive for , and andnegative for ,

alsoin Big-Bang.


Varying constants models6

VARYING CONSTANTS MODELS

In a casewhere , ourscalefactorisreduced to an exoticsingularityscalefactor:

And nowdensity and pressureisexpressed as:


Varying constants models7

VARYING CONSTANTS MODELS

And also:

withthedecelerationparameter:

For energy density and pressurevanish ,

whilethe-indexblows-up to infinitywhichisexactlythecharacteristicsof a -singularity (Dąbrowski and Denkiewicz 2009).


Regularizing singularities

REGULARIZING SINGULARITIES

Big-Bang singularity:

To avoidthe Big-Bang singularities a gravitationalconstantcould be inthe form:

whichis a fasterdecreasethatinthe standard Dirac’scase

Such a time-dependence of G wouldperhaps be less influenced by thegeophysicalconstraints on thetemperature of theEarth (Teller 1948).


Regularizing singularities1

REGULARIZING SINGULARITIES

Exoticsingularities

In order to regularize an SFS singularity by varyingspeed of light we suggestthatthetime-dependence of thespeed of lightisgiven by:

whichaftersubstitutingintopressureequationgives:

SFS singularityisregularized by varyingspeed of lightprovidedthat


Regularizing singularities2

REGULARIZING SINGULARITIES

However, thereis an interestingphysicalconsequence of thefunctionaldependence of thespeed of light. Namely, itgraduallydiminishesreaching zero atthesingularity. In otherwords, thelightslows and eventuallystopsat an SFS singularity. Such an effectispredictedwithintheframework of loop quantum cosmology (LQC), whereitiscalledtheanti-newtonian limit

for , withbeing a criticaldensity (Cailleteau, Mielczarek, Burrau, Grain 2012)


Regularizing singularities3

REGULARIZING SINGULARITIES

One of the standard assumptions on thevariation of thespeed of lightisthatitfollowstheevolution of thescalefactor:

The field equationsnowisexpressed by:

Withitispossible to remove a pressuresingularity

provided , , or , , .


Regularizing singularities4

REGULARIZING SINGULARITIES

Since does not depend on c(t) (for k = 0), thenitisimpossible to strengthen an SFS singularity to become an FSF singularity. Itispossibleonly, if we assumethatthegravitationalconstant G changesin time. Letusthenassumethat

where and


Regularizing singularities5

REGULARIZING SINGULARITIES

Nowdensity and pressureequationsare:

Itfollowsthat an SFS singularity(1 < n < 2) isregularized by varyinggravitationalconstantwhen .

An FSF singularity(0 < n < 1) isregularizedwhen .

Assumingthat we have an SFS singularity and that .

We getthatvarying G maychangean SFS singularityonto a stronger FSF singularitywhen


Regularizing singularities6

REGULARIZING SINGULARITIES

A physicalconsequence of thefunctionaldependence of thegravitationalconstantinisthatthestrength of gravitybecomesinfiniteatthesingularity. Thisisquitereasonableif we want to regularize an infinite (anti)tidalforceatthesingularity. Thisisalsoexactlywhathappensinthestrongcoupling limit of gravity.


Regularizing singularities7

REGULARIZING SINGULARITIES

A hybridcasewhichwould influence bothtypes of singularitiesis:

whichchangesdensity and pressureequationsinto:


Regularizing singularities8

REGULARIZING SINGULARITIES

Singularitiesin (anti-)Chaplygin gas cosmology

Since a couple of years ago, therehasbeen a proposalthatthedark energy can be simulated by a Chaplyginor an anti-Chaplygin gas model. One of theinterestsisthat an anti-Chaplygin gas model allowstheso-calledbig-brakesingularity( , ). whichis a specialcase of a suddenfuturesingularity and .

Theequation of state of the (anti-)Chaplygin gas reads as:

where A > 0 is a constantwiththe unit of the energy density

square.


Regularizing singularities9

REGULARIZING SINGULARITIES

Afterinsertingequation of state of the (anti-) Chaplygin gas intoenergy-momentumconservation law we get:

In order to find an exactsolution, we will first assumethatthespeed of lightisconstantand thatthegravitationalconstantchanges as:


Regularizing singularities10

REGULARIZING SINGULARITIES

Theenergy-momentumconservationnowis:

If we make an assumption we will get:

where


Regularizing singularities11

REGULARIZING SINGULARITIES

The more interesting solution in order to demonstrate regularization of singularities can be obtained in a general case of both varying G = G(t) and c = c(t) though with zero curvature k = 0 case.

Energy-momentum conservation law now is:


Regularizing singularities12

REGULARIZING SINGULARITIES

Solution of theenergy-momentumconservationequationisgiven by:

where .

Density and pressurenowisexpressed by:


Regularizing singularities13

REGULARIZING SINGULARITIES

Puttingthe standard big-bangscalefactor:

we nowhave

whichgive and , provided .Thesingularityat t=0 incan be regularized by taking . In ourcase we have a constantpressure (cosmological term) instead of zero pressure.


Conclusions

CONCLUSIONS

We haveshown by specifyingsomeexamplesthatitispossible to regularizecosmologicalsingularitiesdue to variation of thephysicalconstants. We haveconsideredthisphenomenoninthetheorieswithvaryingspeed of light (VSL) c(t), and withvaryinggravitationalconstant G = G(t).

Interestingly, in order to regularize an SFS by varying c(t), thelightshould stop propagatingat a singularity- thefactwhichappearsintheloop quantum cosmology. On theotherhand, to regularize an SFS by varyinggravitationalconstant - thestrength of gravityhas to becomeinfiniteat a singularity(as inthestrongcoupling limit of gravity(Isham 1976) whichisquitereasonablebecause of therequirement to overcometheinfinite (anti-)tidalforcesatsingularity.


Conclusions1

CONCLUSIONS

Finally, we hopethatvariation of thephysicalconstantswhichleads to regularization of singularitiesmay be usefulinthediscussions of themultiverseconceptgivingthe link through a kind of “fake” singularities to various parts of theuniversewithdifferentphysics. Of courseourdiscussionispreliminary and should be continued by usingappropriatemathematicalformalism of both general relativity and particlephysics.


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