aa r X i v : . [ g r- q c ] O c t October 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM
The Dark Sector Cosmology
Elcio Abdalla and Alessandro Marins
Instituto de F´ısica, Departamento de F´ısica Geral, Universidade de S˜ao Paulo,S˜ao Paulo, CEP 05508-090, Brazil, [email protected] [email protected]
Received Day Month YearRevised Day Month YearThe most important problem in fundamental physics is the description of the contentsof the Universe. Today, we know that 95% thereof is totally unknown. Two thirds ofthat amount is the mysterious Dark Energy described in an interesting and importantreview. We briefly extend here the ideas contained in that review including the moregeneral Dark Sector, that is, Dark Matter and Dark Energy, eventually composing anew physical Sector. Understanding the Dark Sector with precision is paramount forus to be able to understand all the other cosmological parameters comprehensively asmodifications of the modelling could lead to potential biases of inferred parameters ofthe model, such as measurements of the Hubble constant and distance indicators suchas the Baryon Acoustic Oscillations. We discuss several modern methods of observationthat can disentangle the different possible descriptions of the Dark Sector. The possibleapplication of some theoretical developments are also included in this paper as well asa more thorough evaluation of new observational techniques at lower frequencies andgravitational waves.
Keywords : Cosmology, Dark Energy, Dark Matter, Intensity Mapping.PACS numbers:
1. The Standard Cosmological Model and the Dark Sector
The description of the Universe has always been a major and deep problem in theHistory of Human Understanding, as well as in the framework of Modern Physicsbased on Einstein Gravity. The cosmological solution, e. g. the Friedmann-Lemaitre-Robertson-Walker (FLRW) solution was the first attempt to describe the Universeas a whole as a consequence of a physically well established theory, that is, Einsteingravity.However, since 1933 a new ingredient was little by little introduced in the pro-posed theoretical structure of the cosmos: a previously unknown new element in thecosmos, in the beginning thought to be as largely massive as at least 10 times theusual matter density.For a long time the question of whether there exists a hidden Dark Sector wasa burden for a high level understanding of the Universe, since no natural represen-tative from Elementary Particle Standard Model has ever represented such a newCosmological sector. As a matter of fact, this is, in most aspects, a still standing ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM problem.The seminal paper about a Dark Sector (confirmed by others at the time
5, 6 )was based on the movement of galaxies in the Coma cluster (Zwicky actually namedDark Matter at the paper), while in recent times several different observations pointin the same direction. As we know it today, in the so called concordance model,the Dark Sector is constituted by two parts, Dark Matter (DM) and Dark Energy(DE), the former having the usual meaning of gravitationally interacting mass,but oblivious to other standard Particle Physics interactions, while the latter is anew strange kind of object leading to the accelerated expansion of the Universe, aspredicted by observations, by means of a (very) negative pressure, ρ + 3 p/c ≤ p = − ρc corresponds to the addition of a cosmological constantΛ g µν to the right hand side of Einstein Equations, that is,
2, 7 R µν − g µν R = 8 πGT µν − Λ g µν , (1)corresponding to the action S = 116 πG Z R √− g + Λ8 πG Z √− g + S matter . (2)The Standard Cosmological model is based on the above action for S matter corre-sponding to the Elementary Particle Standard Model and some heavy massive fluiddescribing DM. Moreover, the Cosmological constant describes the acceleration ofthe Universe, a fact corroborated by observations. The cosmological constant hasto be, in the above formulation, a Universal constant in view of covariance.There are two basic theoretical problems in the Cosmological Standard Model.The first is the fact that Λ is too small as compared to any Field Theory attemptto describe it in terms of Standard Field Theory. The second is that both DM andDE are equally important at the present era in spite on their different behavior aspredicted by the Standard Cosmological Model. This is the coincidence problem. Therefore, it is natural to consider models of DM and DE with non trivial char-acteristics, that is, not just a fluid and a constant. Actually, this is a fundamentalquestion that should lead to a formulation of a more fundamental theory of theseelements, possibly increasing the scope of the Standard Model of the ElementaryParticles.
2. The Generalized Dark Sector
Several alternative descriptions of DE by itself are very well described in the classicalreview by Copeland, Sami and Tsujikawa. There are, in fact, several remarkablepuzzles about the very existence of DE. Various descriptions and models have beenproposed to describe an accelerating Universe in the above quite remarkable review.Nonetheless, no specific model has, up to now, prevailed as a unified and final(or preferred) description of DE. In that review, the huge number of alternativesfor the explanation and structure of Dark Energy was presented. The case of actober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM Cosmological constant is observationally the simplest, but to cope with its smallvalue is very difficult and one might refer even to an Anthropic principle (see sectionIV of the review for details). Thus, there are several models of Dark Energy, by farthe simplest and most popular is via scalar fields. On the other hand, modificationsof gravity are also very popular and have been discussed in full detail in some partsof the review. String theory has the ability to propose some hints, but now, in thisdirection, there are very constrained possibilities. Nonetheless, a few string inspiredmodels such as DGP may be considered. A Dark Sector as a consequence of ahidden string sector is also possible.
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After models describing DE from a phenomenological holographic point ofview, the simplest description of the Dark Sector is that of an unknown DarkMatter heavy fluid and a Cosmological constant, what is known as the StandardCosmological Model, or ΛCDM model, which, as above mentioned, has problemsin its theoretical interpretation. However, if we leave the realm of a non interactingfluid describing DM and a (Cosmological) constant, the most conservative possi-bility is the description of these elements by means of a field theory, unavoidablyleading to a variety of models of an interacting Dark Sector, that is, a set of fieldsin the Hidden Sector, or the even more complicated possibility of a modification ofEinstein gravity itself.These possibilities are very appealing from the more theoretical point of view,and lead to the idea of an independent Dark Sector, very weakly coupled to thebaryonic sector, or not coupled at all except for gravity, but with an independentdynamics. From the point of view of string theory and beyond, a Dark Sector can benaturally accommodated. As a matter of fact, we can say that a Hidden Sectoris basically mandatory in that context. One obvious case concerns the E × E heterotic string, but a Hidden Sector arising from several different compactificationschemes have been largely discussed in the string literature.
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Usually, the preferred type of DM consists in taking the Lighest SupersymmetricParticle in the Visible Sector (LSVP). The advantage consists in the fact thatbeing the lightest it must be stable and interacts weakly with visible matter. Thereare several candidates, the preferred one being a Neutralino. However, there areseveral other candidates, highly discussed in the literature. Nonetheless, it hasbeen found recently that it might be unstable. Taking for granted the existence of an interaction in the Dark (Hidden) Sector, itwill be, by the same token, natural to consider a Dark Energy arising from anotherHidden Sector field. But what field? A natural possibility allowing for a negativeequation of state is a scalar field, where the potential quite naturally leads to anegative contribution to the pressure. In the string literature scalars are abundant.Therefore, it is natural to consider models of the Dark Sector consistent with theidea of describing Dark Matter by a fermion and a scalar describing Dark Energy. Possibilities of introducing vector fields, as implied by some string inspired modelsis also feasible. Moreover, fermions can easily accommodate the idea of Cold Darkctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM Matter.
3. State of the Art Observational Methods in Cosmology
From the point of view of observations, constraints on Cosmology are, nowadays,much stronger. We are in a so called precision cosmology age. Data arise fromdifferent directions:1.
Dark Energy Direct Observation: Structure of the Hubble law determiningcosmological acceleration for relatively small Redshift data ( z < ) Supernovae observations are well suited, since some time, to confirm and improveHubble’s result. It has been shown from Supernovae observations that to morethan 7 σ the data are compatible with an accelerating Universe as described by apositive Cosmological Constant (CC). The amount of DE (CC) is of the order of2/3 of the critical value. The results are, observationally, very well grounded andobtained by different groups.2. Dark Matter amount from direct observation.
Direct Dark Matter observations have been done since almost a century andcontinue to be performed. Although it has led people to propose alternatives suchas MOND (modified gravity), the existence of a Dark Sector is, from the side ofDM, basically undeniable. Indeed, modifications of gravity at large scales can ex-plain higher speeds of astrophysical objects around a galaxy or a cluster. However,Modified Gravity cannot explain the CMB anisotropies distributions, which requirea definite amount of Dark Matter. Constraints from the Microwave Background ob-servations are very strong, especially now after two decades of detailed observationsthat we comment below.3.
Constraints on cosmological parameters from CMB observations (COBE,WMAP and, more recently, Planck)
The observed power spectrum from Cosmological Microwave Background (CMB)is one of the finest observations in nature. CMB is the most perfect Black Body,characterized by a temperature of T ≈ . DE = 0 .
685 and Ω M = 0 . K = − . σ . This is also consistentwith the inflationary scenario.ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM Constraints from Baryonic Acoustic Oscillations as standard rules.
Some years ago, it has been established that relic waves left by the baryonicelectric interaction previous to decoupling could now be observed as giant correla-tions of the rough size of 150 Mpc, the so called Baryonic Acoustic Oscillations(BAO). The size of that wave stands as a standard ruler allowing for a new set ofconstraints on cosmological parameters.5. Observations from weak lensing effects.
Lensing as an effect of General Relativity is one hundred years old and remindsus of the first confirmation of General Relativity. Now, the consequence of the wellknown lensing process arising from intervening matter with respect to observationhas an important effect in the power spectrum. Results arising from Redshift Space Distortion.
The most precise measurement we can have in cosmology is the redshift. Itis directly related to distance as a consequence of Hubble law. However, localmovements can interfere with the exactness of the relation, leading to distortionsin view of local relative motions as e.g. inside a galaxy, what leads to distortionsin the redshift map. This is an important piece of information to deal with largescale structure maps.The redshift-space distortion (RSD) has been measured in the past few yearswith higher precision. It can give information about the large scale structure andcosmological parameters of relevance for model building, because the local move-ment of galaxies towards higher density distribution implies a peculiar componentto the redshift as compared to the Hubble predicted value. It is thus a powerfulcomplementary observation to break the possible degeneracy in cosmological mod-els. This is also because the dynamical growth history in the cosmological structurecan be distinct even in case they display the same evolution in the background. Itis expected that including the large scale structure information by adding the RSDmeasurements can provide a rich background on theoretical models of cosmology. Optical data constraining Large Scale distribution of Matter.
The above point is related to the structure of perturbations at large scales.Perturbation of Einstein Equations can have integer spins from zero to two. Spin 2perturbations concern gravitational waves. Vector perturbations decay quickly andare not cosmologically important. Scalar perturbations remain as the template fordensity fluctuations.Today it is common to have maps of the Universe from observations. From thecomparison of such so called mocks with the gravitational theory supplemented bythe matter model used can provide a way to constrain the cosmological parameters.8.
Future Developments
In the future, constraints from gravitational waves observations can be incorpo-rate in this list. Indeed, we can show that observations of these waves can be usedas standard sirens to improve Hubble data (see below).By the same token, also in the future, neutrino observations, especially neutrinomasses, can be used as constraints in Cosmology. ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM Observations of the 21 cm line by means of the technique of Intensity Mapping(what overlaps with some of the previous results)
Hydrogen is the most common visible element (baryonic) of the Universe. A mapof the Hydrogen distribution is an valuable template of matter and much easier toobtain as we shall see. It is also natural to suppose that the Hydrogen distributionmay also be a good template of Dark Matter, assuming that matter in generalfollows a standard (possibly biased) distribution.Usually, the Large Scale Structure by means of a redshift survey is an expensivemethod, and alternatives are searched, see for instance the JPAS project and itsrole in the Dark Sector search. On the other hand, the Hydrogen atom emits a very typical radiation corre-sponding to the hyperfine transition, the 21 cm line. Although the higher statebeing quite stable, Hydrogen is common enough to provide a way to measure dis-tribution by the technique of Intensity Mapping (IM), that is, by the averageintensity of the 21cm line.The 21cm emission of the underlying matter, can be 50 times more efficientthan the previous technique using individual galaxies. Therefore, progress can bemade with much smaller scale instruments, as for instance BINGO. Today, severalprojects in Radio Astronomy aim using this method to probe the Dark Sector.
4. Statistical Methods in Cosmology
Cosmology is the result of solutions of the Einstein Field Equations coupled tothe Standard Particle Model. Therefore, it can be seen as a classical solution of ahighly nonlinear field theory, including the particle fields. The metric and possiblyphenomenological fluids are usually used in the impossibility of directly describingcertain sophisticated solutions from first principles in a general field theory.Given the initial conditions from inflation and its probabilistic character, thedensity profile and correlation functions are the main objects we can aim to ob-serve and describe. A sophisticated and detailed cosmology is described by correla-tors, whatever mathematical space is used to describe it (real, Fourier, harmonic,wavelets, among others). Hard data analysis is necessary to extract as accurate aspossible cosmological information.Cosmological surveys, in current and next generations, explore a huge amountof data, with increasingly larger areas and greater analysis depth as well as greaterresolution. Sophisticated data analysis methods are needed to deal with the volumeand accuracy of the information. As an example, the next generation of galaxysurveys is expected to obtain up to billions of galaxies.
5. Intensity Mapping: Exploring 21cm line cosmologicalinformation
The standard approach to probing Large Scale Structure (LSS) by means of a largegalaxy-redshift survey has been extensively used in the optical and far infraredctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM bands. Galaxies are used as tracers of the underlying total matter distribution.However, galaxy surveys have a threshold for a minimum flux. Only galaxies abovethis value can be individually detected. These surveys require a large integrationtime of observation to obtain good determination of the galaxy redshifts from theiroptical spectra. Considering the epoch before the existence of structure, such asreionisation or even before, it is necessary to appeal to other types of survey.In the past two decades another method has been developed and used to explorethe radio band, called Intensity Mapping (IM), that explores a larger area of thesky in a shorter time. Instead of galaxy surveys, IM does not require identifyingindividual objects thus not having a threshold of the minimum flux. IM, instead ofidentifying galaxies, measures the total flux from many galaxies which will underlinematter. Therefore, we can be use HI as a matter tracer. Observing 21 cm HI emissionwe can explore a long time range of the life of the Universe since ionization epoch.In post-reionisation (low redshift), most of (ionised) hydrogen are outside galaxiesand HI are inside galaxies in high-density gas clouds systems that are shielded fromionised UV photons.
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IM can be performed by low-resolutions interferometers or by single-dish exper-iments. There are several examples, CHIME and SKA
32, 38 are interferometers.In the case of SKA (in development) that will cover a redshift range until z ∼ a andBINGO that will cover different sky regions and redshift ranges post-reionisation.In the reionisation epoch the 21cm power spectrum is highly dependent on thedetails of the reionisation process and post-reionisation although it does not dependof the description of the process, the signal is very weak, since most of the HI isdestroyed during the reionisation epoch, and the signal is highly contaminated.Therefore, the main challenge for HI IM surveys are the astrophysical contaminationand the systematic effects about the observed signal. To reconstruct the 21cm signaltechniques already used in CMB experiments classified as Component Separation are necessary. The 21cm IM has the advantage that the astrophysical componentsvary smoothly with frequency and they have stronger signal than the 21cm line,facts that can be used to reconstruct the signal. Different techniques exploringdifferent characteristics about foregrounds or about 21cm signal are available orunder development to disentangle the signals. As an example we cite GNILC and GMCA that are also used in case of the CMB. Other lines and atoms or molecules can also be used in IM such as CO(1-0) b ,CO(2-1), CO(3-2) among others.
6. Dark Energy and BAO from 21cm IM
The accelerated expansion of the Universe is a formidable challenge. What mecha-nism or component is actually causing this behavior is a big puzzle and an extraor- a http://meerkat2016.ska.ac.za/ b https://kipac.stanford.edu/research/projects/co-mapping-array-pathfinder-comap ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM dinary way to study it is through BAO at low redshifts, when, according to whatstudies and analyses of the data have shown us, the DE becomes relevant in thedynamics of the expansion of the Universe. The post-reionisation epoch is a valuablesource of information about the nature of DE and can be studied from BAO, thatis, an information from a primordial epoch of the Universe.There was a period when baryons and photons were coupled, building a hotplasma. The Electromagnetic coupling leading to Compton scattering builds pat-terns in the distribution of the matter and photons, but with the expansion ofthe Universe and its cooling the patterns decrease and freeze when photons andbaryons decouple. These patterns can be seen both in the CMB spectrum and inthe galaxy spectrum today. Considering a spherical perturbation of matter den-sity, it will propagate outwards (in relation to the center of the perturbation) witha sound speed proportional to the light speed. It is redshift dependent. That is,the perturbations spread as sound waves on this plasma and stops its propagationwhen baryons and photons decouple. Such a process leads to a characteristic peakin the matter correlator that, when seen in Fourier (or harmonic) space, appearsas damped oscillations in a given region of scale. The phenomenon is called BaryonAcoustic Oscillation (BAO). In real space that peak distance is about 150 Mpc andis called the sound horizon corresponding to the distance travelled by the soundwave until shortly after decoupling (drag epoch). HI, being a matter tracer, mustdisplay such a pattern too and this property must appear in its power spectrum. Inthis scenario, the BINGO telescope aims to detect BAO in radio frequency. Thisis how the 21cm IM method can be used.But how exactly can we use BAO to study Dark Energy? BAO carried infor-mation about the primordial Universe and in the corresponding redshift of themeasurement. In general, cosmological length, and therefore distance, depends onwhat the Universe is made of and in what proportions. The sound horizon lengthdepends on the history of the Universe until the drag epoch and its distortionsmeasured in radial and transverse directions also depend on the properties of theUniverse. Still, sound horizon is a fixed value of the comoving length for all timesafter drag epoch and can be used to calibrate distance, that is, it is a standardcosmological ruler .
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Thus, BAO can be used for both astronomical calibrationand cosmological parameters constraints.In the BINGO case, the angular power spectrum will be used as data and BAOappears as fluctuations in a given multipole range. However, in order to see thisfluctuation, the component separation must be as accurate as possible, such thatcontamination and errors in the data do not suppress fluctuations. In addition toforegrounds contamination, that is about a thousand times stronger than 21cmsignal, there are contaminations such as polarization leakage, temper-ature system, Radio Frequency Interference (RFI), among others, that are smallerthan foregrounds, but also very important contaminations that need to be preciselyunderstood for the pipeline construction and must be properly extracted.The large covered area and modern design make BINGO, in addition to a greatctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM cost benefit, a rich source of new information, important in itself and also importantto be treated together with the data already available, with a coverage of 5400 deg and in the range z = 0.13-0.48, exploring the galactic south through two dishes ofapproximately 40 m in diameter and the signal collecting horns.
7. New Trends in Cosmology and Astrophysics7.1.
Gravitational Waves
For about 100 years, gravitational waves eluded physicists: it had not been possibleto obtain a connection between theory and experiments, the latter were lackinguseful results. The only hint to gravitational wave was the loss of energy in a binarysystem.In the last few years enormous advances have been made in the quest of gravi-tational waves, which have been finally explicitly encountered. But this is not theonly good news, it can also be used in cosmology: the amplitude of gravitationalwaves is related to the measure of the luminosity distance from the source. This im-plies a possibility to establish Hubble law in an independent way, that is, obtaininga new redshift/distance diagram. We say that gravitational waves can be used asstandard sirens, as in gravitational waves originating from the collision of a pair ofneutron stars. A few years ago, (GW170817) and its electromagnetic counterpart(GRB170817A) were both detected.Therefore, Gravitational Waves can also be used to investigate cosmology (andconsequently also the Dark Sector) besides electromagnetic based observations.The luminosity distance in a flat space-time is given by the expression d L ( z ) = c (1 + z ) H Z z dz ′ E ( z ′ , ~ Ω) , (3)where E ( z, ~ Ω) = H ( z, ~ Ω) /H is the normalized Hubble function, depending on theredshift z and the parameter set ~ Ω characterizing the cosmological model (relativedensities).Gravitational Wave amplitudes for a binary system depend on the chirp mass, M c ≡ M η / ≡ ( m + m ) η / where η = m m /M . It can be measured by theGravitational Wave signal phasing,
51, 52 defining the luminosity distance d L fromthe GW amplitude. The relation between the luminosity distance and the amplitudeis the core of the importance of gravitational waves for cosmological investigation,we need just one of them, and it determines the other object.Interferometers can measure the h ( t ). In a gauge described by “plus” and “times”modes h + , h × , the strain is given by h ( t ) = F + ( θ, φ, ψ ) h + ( t ) + F × ( θ, φ, ψ ) h × ( t ) , (4)where the F + , × characterize the beam, ψ is the polarization angle and ( θ, φ ) givethe position of the source.ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM The observed chirp mass is related to the physical chirp mass by a redshift factor, M c,obs = (1 + z ) M c,phys . The Fourier transform H ( f ) of the strain h ( t ) is H ( f ) = A f − / e i Ψ( f ) , (5)where Ψ( f ) is a phase and the amplitude is proportional to a power of the chirpmass, A ∼ M / c .We can generate a mock catalog d L − z by coalescence of BNS pair in themass range [1 − M ⊙ for each individual neutron star. The redshift distribution ofthe observable sources follow a calculable function in terms of another functiondescribing the redshift evolution of the burst rate. We have to use also the formationrate of massive binaries and the delay time distribution P ( t d ) which describesthe minimal delay time for a binary system to evolve to merger. The cosmic starformation rate based in Gamma-Ray Bursts (GRB) rate is also needed. We canadopt R BNS ( z = 0) = 920 Gpc − yr − as estimated by LIGO/Virgo observation runwith the assumption that the mass distribution of neutron stars follows a gaussianmass distribution.The Hubble expansion can be estimated in an independent way and a new cos-mological test can be obtained. Therefore, gravitational waves as standard sirenscan be a very useful cosmological probe in the near future. Third generation detec-tors as the case of the Einstein Telescope can improve current Gravitational Wavesobservations and have sensibility to detect an order of 10 events per year, which isenough to impose constraints as good as the current cosmological probes.Recently, forecasts about interacting Dark Sector cosmology has been proposedwith good results pointing to further constraints. As a result there is a decrease ofalmost ∼
90% in error in relation to CMB data only, which suggests that standardsirens can help solving the tension in H between CMB and Supernovae in the nearfuture. Some of the results have been obtained by Yang et al and Rhavia et al
55, 56 for interacting vacuum-energy models, as well as in interacting DE/DM models. Authors found an improvement of 17% in the coupling and 35% in H with theaddition of GW simulated data to CMB+BAO+SN data, and the reduction of theuncertainty on the DM-DE coupling by a factor of 5. This shows a very intersting interplay of different types of physics pointingdirections in physics and cosmology understanding.
Other Astrophysical Objects
New physics is at the verge of being discovered. Even clearer is the fact that newobjects in the sky generally provide new constraints in our description of the cosmos.Until some time ago, the only information about the sky came from the directoptical observation. Now, with further knowledge and observations of neutrino prop-erties, gravitational waves as above, Gamma Ray Bursts and other minor objects,further data for cosmology reconstruction shall follow.ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM Fast Radio Bursts
Discovered in 2007, FRBs are short bursts (0 . −
161 Jy) of radio photons ofunknown origin
60, 61 and several possible explanations, a question left undecided upto now. The time delay of photons with different frequencies is characterized by theso called Dispersion Measure, R n e dl , which basically informs us how much space ithas travelled. From the dispersion measure we know that FRBs are extra galacticobjects. Today more than a hundred such events have been observed; several areknew. If we are able to define their position we are going to be able to have a furthertest of cosmological parameters. Direct observation from Radio Telescopes (BINGOis one such, there are several others
31, 50 ) is going to be possible. In case we knowtheir position with accuracy (some outriggers should be enough adjoining a RadioTelescope as BINGO) we shall be able to know their host galaxy, therefore theirdistance, allowing us to characterize much of their parameters.Several FRBs with frequencies from 300 MHz to 8 GHz have been recentlyobserved.
62, 63
We can use this type of information not only to constrain cosmologicalparameters but also to test the Weak Equivalence Principle as well as gettingconstraints on the photon mass and compact DM. We can consider the InterGalactic Medium and foresee other possible applications. FRBs have been seen in various experiments such as the Australian SquareKilometre Array Pathfinder, the Parkes Radio Telescope, the CHIME, theUTMOST telescope, the GBT, Arecibo and Apertif.
71, 73, 75
Radio Telescopes at the verge of starting to work will be able to make severalobservations of FRBs. In particular, the BINGO telescope will possibly be ableto evaluate its host galaxy, thus important cosmological conclusions can be drawnfrom them, especially concerning the structure of acceleration and thus Dark Energy,besides the formidable problem of the astrophysical structure of FRBs.
8. Conclusions
Today, cosmology is possibly the hottest area of research in fundamental physics. Itcan provide us a view of a world at least 20 times larger than ours (with respect toits content), in case the Dark Sector has the same richness as the Baryonic Sector,what is not beyond all possibilities. In this direction, DE is the most tantalizing in-formation, certainly beyond our common sense knowledge. In particular, DE deniesthe Strong Energy Condition, a property quite unthinkable in the near past!In view of these properties, it is no doubt that the physical properties of apurported Dark Sector are (or can be) very peculiar and encompasses non trivialmodifications of Standard Particle Theory and models. Previous important resultsseem to pale before these properties.
Acknowledgments
We would like to thank FAPESP and CNPQ (Brazil) for long standing financialsupport.ctober 19, 2020 0:31 WSPC/INSTRUCTION FILE ws-ijmpdDEDM References
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