Astroparticle Physics and Cosmology: Perspectives in the Multimessenger Era

296 Pages·2020·4.053 MB·English

by  Subhendra Mohanty

Lecture Notes in Physics
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Lecture Notes in Physics
Volume 975
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Subhendra Mohanty
Astroparticle Physics
and Cosmology
Perspectives in the Multimessenger Era
SubhendraMohanty
TheoryDivision
PhysicalResearchLaboratory
Ahmedabad,Gujarat,India
ISSN0075-8450 ISSN1616-6361 (electronic)
LectureNotesinPhysics
ISBN978-3-030-56200-7 ISBN978-3-030-56201-4 (eBook)
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Preface
In the last decade, there have been several seminal discoveries starting with the
Higgs boson at the LHC (2012); neutrinos with PeV energies at IceCube (2013);
detection of gravitational waves from black hole and neutron star mergers by
LIGO (2016) and the first picture of the black hole at the centre of the M87
galaxyby the EHT (2019).This comesafter the successof the solar, atmospheric
and reactor neutrino observation experiments in the last three decades and the
cosmic microwave anisotropy measurement experiments (COBE (1989–1993),
WMAP(2001–2011)andPLANCK(2009–2011)).Terrestrialdarkmatterdetection
experimentscontinuetoputlimitsonthemassandcross-sectionofdarkmatter(if
at all they are elementary particles). Astronomical observations are ongoing in a
very large range of the electromagnetic spectrum (from radio to gamma rays) in
addition to the observations of high energy neutrinos by IceCube. This ongoing
multi-prongedobservationof the universe will help us to answer the fundamental
questionsabouttheunderlyingtheoriesthatgoverntheuniverse.
Inthisbook,weexplorethetheoreticalconsequencesofthesemulti-messenger
signals from the universe. A graduate student or researcher who is curious about
learning a particular research topic may delve into the chapter of their choice to
getanintroductiontothesubject.Thetreatmentismorepedagogicalandfocussed
comparedwith a review article. The main results discussed are worked out in the
text.
In Chap.1, we give a survey of the recent experimental observations, which
started the multi-messenger era of astronomical observations like observations of
gravitationalwaves,gammarays,neutrinosandcosmicraysfromthesamesource
(e.g. blazers). We also list other important unsolved issues like final unobserved
signal of the inflation paradigm, namely the observation of inflation-generated
gravitational waves in the early universe via the measurement of the B-mode
polarizationoftheCMBsignal.
Dark matter is amongst the hottest areas of enquiry in particle physics and
cosmology. In Chap.2, we discuss the phenomenology of dark matter at cosmo-
logicalandgalacticscales.DirectdetectionexperimentslikeXenon-1Thaveruled
out a large swathe of the mass vs DM–nucleon cross-section parameter space
challenging the conventional paradigm of the ∼100GeV weakly interacting dark
matter,wheretheobservedrelicdensityisnaturallyaccountedfor.Newmechanisms
vii
viii Preface
for explainingthe relic density like the freeze-in productionof dark matter or the
3 → 2annihilationprocessarerequiredforevadingthestringentconstraintsfrom
directdetectionexperiments.Darkmattermaybeverylightwithamassof10−22eV,
ortheymaynotbeelementaryparticlesatallandmaybeprimordialblackholes.
Large-scalegalacticsurveyssuchastheSloanDigitalSkySurvey,DarkEnergy
Survey and Baryon Oscillations Spectroscopy Survey are increasingly providing
data aboutthe distribution of matter in the universeand providea scope for us to
test theories of dark matter, dark energy, neutrino mass, etc. To test theory with
observations from the survey, we need to understand perturbations of the metric
andmatter (darkmatter,baryons,photons,neutrinos)in the frameworkof general
relativity.WedothisinChap.3.
In Chap.4, we study the effect of perturbations on the cosmic microwave
backgroundanisotropy spectrum. The observationsof COBE, WMAP, PLANCK,
DESI,SPT,etc.turnedcosmologyintoprecisionscience.Futureobservationswill
tell us about the existence (or not) of B-mode polarization, which will test the
theories of inflation. CMB can also be used to study the interactions of the dark
sector like neutrino–darkmatter interactionsor neutrino–darkenergyinteractions.
WelaydownthebasicsofthetheoryofCMBanisotropyaimedatnon-expertsinthe
subjectwho wouldlike to dive in and make predictionsbased on theoriesof their
choiceforongoingandfutureobservations.
InChap.5,wediscussmodelsofinflation,whichareconsistentwiththestringent
limits on the tensor-to-scalar ratio and spectral index placed by PLANCK. There
are a few well-motivated inflation models that make the cut, namely natural
inflation, curvature-coupled Higgs inflation, R2 Starobinsky inflation and the no-
scale supergravity models. We discuss the pros and cons of each of these models
anddiscusstheirotherphenomenologicalconsequenceandfutureprospectsinCMB
andLSSobservations.
The discovery of the Higgs boson completed the last element in the particle
spectrum envisaged in the standard model. The discovery of this first elementary
scalar particle brings in several questions regarding the Higgs potential. In the
standard model, the Higgs potential becomes negative at energy scales of ∼1011
GeV.Istheuniversestableagainsttunnellingtoanegative(Higgspotential)energy
phase?WhatadditionalparticlescanmaketheHiggspotentialstableormetastable
(thetimescaletunnellingissmallerthanthelifetimeoftheuniverse)?
In Chap.6, we address these questions. We develop the idea of effective
potentialofscalarfields.We discusstheColeman–Weinberg(oneloopatallorder
in coupling) corrections to the tree-level potential. We also derive the effective
potential at finite temperature, which will decide the nature of phase transition
during symmetry breaking as the universe cools. Phase transitions in the early
universecangenerategravitationalwavesthatmaybeobservedinLIGOorfuture
gravitationalwavedetectors.
In Chap.7, we discuss gravitational waves. The gravitational wave energy
radiatedrate bybinarystarsis calculatedusingthe (quicker)effectivefieldtheory
technique and the result compared to the classical derivation. Energy loss rate of
other possible light scalars like axions from black holes or neutron stars is also
Preface ix
derived.Thegravitationalwaveformexpectedatthedetectorsfrombinarymergers
isderived.Thestochasticgravitationalwavesfromphasetransitions,whichmaybe
observedingravitationalwavedetectors,areworkedout.
InChap.8,westudyblackholes.Blackholemergershavebeenobservedthrough
their gravitational signals, and the ring down of the black holes has been seen in
theLIGOobservations(2016).Fromthegravitationalwaveobservations,themass
and spin of the black holes can be estimated. Moreover,recently there is a direct
observationoftheblackholeshadowbythe EventHorizonTelescopeteamofthe
supermassiveblackholeatthecentreofM87galaxy.Theseobservationsareagood
motivationforstudyingthedetailsoftherotatingblackholesaswellasmoregeneral
typesofblackholeslikethedilation-axionblackholespredictedfromstringtheory.
ThedeviationfromtheKerrmetricmaybeobservableingravitationalwavesignals
ormoredirectlyfromtheshapeandsizeofthephotonshadowsofthesuper-massive
galacticcentreblackholes.Kerrblackholesmayalsogeneratehighenergyparticles
bythemechanismofsuper-radiancethatwewilldiscusslaterinthatchapter.
We hope that the reader will find the subjects covered interesting and be
motivatedtodiveintotheresearchworkinthisfield.
I thank the students Surya Nayak, Prafulla Panda, Sarira Sahu, Anshu Gupta,
Akhilesh Nautiyal, Suratna Das, SoumyaRao, Moumita Das, TanushreeKaushik,
Gaurav Tomar, Girish Chakravarti, Bhavesh Chauhan, Ashish Narang, Priyank
Parashari,PrakrutChaubalandTanmayPoddarfortheirwonderfulcollaborations.
I thank the postdoctoral fellows I have worked with namely, Peter Stockinger,
Kaushik Bhattacharya, Joydeep Chakrabortty, Gaurav Goswami, Ila Garg, Ujjal
KumarDey,NaveenSingh,NajimuddinKhan,SampurnAnand,ArindamMazum-
dar,SoumyaSadhukhan,SoumyaJana,SukannyaBhattacharya,AyonPatra,Tripu-
rariSrivastava,AbhassKumarandAbhijitSahaforkeepingmeup-to-dateaboutthe
newavenuesofresearchovertheyears.Manyofmycollaboratorshavecontributed
plotsandillustrationsforthisbook.Ithankthemallfortheirimmensehelp.
I thank my long-term collaborators Eduard Masso, Anjan Joshipura, Durga
PrasadRoy,SandipPakvasa,GaetanoLambiase,AragamPrasannaandothersfrom
whomIhavelearntmuchofwhatappearsinthisbook.
IthankmycolleaguesatPRLfortheirsupport.
I thank my wife Srubabati and daughter Anushmita for among other things
keepingmefedandwateredinthetryingtimesduringthecompletionofthebook.
I thank B. Ananthanaryan, Indian Institute of Science, Bangalore (Editorial
BoardmemberofSpringerBriefsinPhysics)forhisencouragementandsupport.
Andlastbutnottheleast,IthankmySpringerEditorLisaScaloneforpatiently
guidingmetillthecompletionofthisbook.
Ahmedabad,India SubhendraMohanty
May2020
Contents
1 Introduction .................................................................. 1
1.1 GravitationalWaveObservationbyLIGO ........................... 1
1.2 Multi-MessengerSignalatLIGO,VIRGO,IceCubeandFermi.... 2
1.3 IceCubeObservationofPeVNeutrinos .............................. 3
1.4 LSSandCMB ......................................................... 4
1.5 PhaseTransitionsandStochasticGravitationalWaves .............. 5
References..................................................................... 6
2 DarkMatter.................................................................. 9
2.1 Introduction............................................................ 9
2.2 DarkMatterintheGalaxies........................................... 10
2.2.1 IsothermalDistribution...................................... 11
2.2.2 NFWProfile.................................................. 13
2.2.3 BurkertProfile................................................ 14
2.2.4 TheLocalDensityofDarkMatter.......................... 14
2.3 DarkMatteratCosmologicalScales.................................. 14
2.3.1 RelicDensityofDarkMatterintheUniverse.............. 15
2.3.2 BoltzmannEquation......................................... 16
2.3.3 RelicDensityofColdDarkMatter.......................... 19
2.3.4 SelfInteractingDarkMatter................................. 26
2.3.5 ColdDarkMatterRelicbyFreeze-in ....................... 29
2.3.6 Ultra-LightDarkMatter .................................... 32
2.4 DirectDetectionofWIMPDarkMatter.............................. 33
2.4.1 AnnualModulationoftheSignal ........................... 34
2.4.2 FromNucleonCrossSectiontoNuclearScattering
Rates.......................................................... 35
2.4.3 FromQuarksCouplingstoNuclearCouplingsof
DarkMatter .................................................. 37
2.4.4 Spin-DependentCrossSection.............................. 41
2.4.5 InelasticDarkMatter ........................................ 43
2.5 DarkMatterSignalsinHighEnergyPhotonsandNeutrinos
Observations........................................................... 44
2.6 Conclusion............................................................. 46
References..................................................................... 46
xi