Indirect Searches for Gravitino Dark Matter Michael Grefe Departamento de Física Teórica Instituto de Física Teórica UAM/CSIC Universidad Autónoma de Madrid PLANCK 202 From the Planck Scale to the Electroweak Scale Warszawa 30 May 202 Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 / 5
Motivation for Unstable Gravitino Dark Matter What Do We Know about Dark Matter? I Dark matter is observed on various scales through its gravitational interaction I Dark matter contributes significantly to the energy density of the universe [van Albada et al. (985)] [Clowe et al. (2006)] [NASA / WMAP Science Team] I Dark matter properties known from observations: No electromagnetic and strong interactions At least gravitational and at most weak-scale interactions Non-baryonic Cold (maybe warm) Long-lived on cosmological time scales but not necessarily stable! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter [NASA / WMAP Science Team] PLANCK 202 30 May 202 2 / 5
Motivation for Unstable Gravitino Dark Matter What Do We Know about Dark Matter? I Dark matter is observed on various scales through its gravitational interaction I Dark matter contributes significantly to the energy density of the universe [van Albada et al. (985)] [Clowe et al. (2006)] [NASA / WMAP Science Team] I Dark matter properties known from observations: No electromagnetic and strong interactions At least gravitational and at most weak-scale interactions Non-baryonic Cold (maybe warm) Long-lived on cosmological time scales but not necessarily stable! [NASA / WMAP Science Team] Particle dark matter could be a (super)wimp with lifetime age of the universe! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 2 / 5
Motivation for Unstable Gravitino Dark Matter Why Are We Interested in Unstable Gravitino Dark Matter? Supergravity predicts the gravitino as the spin-3/2 superpartner of the graviton Gravitinos are produced thermally after inflation: ( ) ( Ω 3/2 h 2 00 GeV 0.27 T R 0 0 GeV m 3/2 Problem in scenarios with neutralino dark matter: ) ( ) 2 m g TeV [Bolz et al. (200)] Thermal leptogenesis requires high reheating temperature: T R 0 9 GeV [Davidson et al. (2002)] Late gravitino decays are in conflict with BBN Cosmological gravitino problem Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 3 / 5
Motivation for Unstable Gravitino Dark Matter Why Are We Interested in Unstable Gravitino Dark Matter? Supergravity predicts the gravitino as the spin-3/2 superpartner of the graviton Gravitinos are produced thermally after inflation: ( ) ( Ω 3/2 h 2 00 GeV 0.27 T R 0 0 GeV m 3/2 Problem in scenarios with neutralino dark matter: ) ( ) 2 m g TeV [Bolz et al. (200)] Thermal leptogenesis requires high reheating temperature: T R 0 9 GeV [Davidson et al. (2002)] Late gravitino decays are in conflict with BBN Cosmological gravitino problem Possible solution: Gravitino is the LSP and thus stable! Correct relic density possible for m 3/2 > O(0) GeV Gravitino dark matter Still problematic: Late NLSP decays are in conflict with BBN Cosmological gravitino problem Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 3 / 5
Motivation for Unstable Gravitino Dark Matter Why Are We Interested in Unstable Gravitino Dark Matter? Supergravity predicts the gravitino as the spin-3/2 superpartner of the graviton Gravitinos are produced thermally after inflation: ( ) ( Ω 3/2 h 2 00 GeV 0.27 T R 0 0 GeV m 3/2 Problem in scenarios with neutralino dark matter: ) ( ) 2 m g TeV [Bolz et al. (200)] Thermal leptogenesis requires high reheating temperature: T R 0 9 GeV [Davidson et al. (2002)] Late gravitino decays are in conflict with BBN Cosmological gravitino problem Possible solution: Gravitino is the LSP and thus stable! Correct relic density possible for m 3/2 > O(0) GeV Gravitino dark matter Still problematic: Late NLSP decays are in conflict with BBN Cosmological gravitino problem Possible solution: R parity is not exactly conserved! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 3 / 5
Gravitino Dark Matter with Broken R Parity Gravitino Dark Matter with Bilinear R-Parity Violation Bilinear R-Parity Violation: W /Rp = µ i H ul i, L soft /R p = B i H u l i + m 2 H d l i H d l i + h.c. Only lepton number violated Proton remains stable! Cosmological bounds on R-violating couplings (parametrized by ξ) Lower bound: The NLSP must decay fast enough to evade BBN constraints: Upper bound: The lepton/baryon asymmetry must not be washed out: Gravitino decay suppressed by Planck scale and small R-parity violation ξ 0 ξ 0 7 Gravitino decay width: Γ 3/2 ξ2 m 3 3/2 M 2 Pl The gravitino lifetime exceeds the age of the universe by many orders of magnitude The unstable gravitino is a well-motivated and viable dark matter candidate! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 4 / 5
Gravitino Dark Matter with Broken R Parity Gravitino Dark Matter with Bilinear R-Parity Violation Bilinear R-Parity Violation: W /Rp = µ i H ul i, L soft /R p = B i H u l i + m 2 H d l i H d l i + h.c. Only lepton number violated Proton remains stable! Cosmological bounds on R-violating couplings (parametrized by ξ) Lower bound: The NLSP must decay fast enough to evade BBN constraints: Upper bound: The lepton/baryon asymmetry must not be washed out: Gravitino decay suppressed by Planck scale and small R-parity violation ξ 0 ξ 0 7 Gravitino decay width: Γ 3/2 ξ2 m 3 3/2 M 2 Pl The gravitino lifetime exceeds the age of the universe by many orders of magnitude The unstable gravitino is a well-motivated and viable dark matter candidate! Rich phenomenology instead of elusive gravitinos A long-lived NLSP could be observed at the LHC [Bobrovskyi et al. (200, 20)] Gravitino decays lead to possibly observable signals at indirect detection experiments Gravitinos could be indirectly observed at colliders and in the spectra of cosmic rays! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 4 / 5
Gravitino Dark Matter with Broken R Parity Gravitino Decay Channels Several contributing decay channels: ψ 3/2 γ ν i, Z ν i, h ν i, W l i For m 3/2 < m W three-body decays can play an important role [Choi et al. (200)] Ratio between γ ν i and other channels is model-dependent 00 Ψ32ZΝi, m32 00 GeV Branching Ratio 0. 0.0 0 3 0 4 0 5 Γ Z Νi W i Wi ZΝi hνi 0 00 000 0 000 Gravitino MassGeV ΓΝ i Νe Γ ΝΜ d 0 3 ΝΤ p 0.0 0. 0 00 Kinetic EnergyGeV Gravitino decays produce spectra of stable cosmic rays: γ, e, p, ν e/µ/τ, d Two-body decay spectra generated with PYTHIA Deuteron coalescence treated on event-by-event basis in PYTHIA [Kadastik et al. (2009)] Spectrum dndlog 0 T 0 0. 0.0 0.00 e Νi Ν e Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 5 / 5
Gravitino Dark Matter with Broken R Parity Gravitino Decay Channels Several contributing decay channels: ψ 3/2 γ ν i, Z ν i, h ν i, W l i For m 3/2 < m W three-body decays can play an important role [Choi et al. (200)] Ratio between γ ν i and other channels is model-dependent 00 Ψ32ZΝi, m32 00 GeV Branching Ratio 0. 0.0 0 3 0 4 0 5 Γ Z Νi W i Wi ZΝi hνi 0 00 000 0 000 Gravitino MassGeV ΓΝ i Νe Γ ΝΜ d 0 3 ΝΤ p 0.0 0. 0 00 Kinetic EnergyGeV Gravitino decays produce spectra of stable cosmic rays: γ, e, p, ν e/µ/τ, d Two-body decay spectra generated with PYTHIA Deuteron coalescence treated on event-by-event basis in PYTHIA [Kadastik et al. (2009)] Basis for phenomenology of indirect gravitino dark matter searches! Spectrum dndlog 0 T 0 0. 0.0 0.00 e Νi Ν e Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 5 / 5
Indirect Detection of Gravitino Dark Matter Cosmic-Ray Propagation I Cosmic rays from gravitino decays propagate through the Milky Way I Experiments observe spectra of gamma rays, charged cosmic rays and neutrinos [NASA E/PO, SSU, Aurore Simonnet] Michael Grefe (IFT UAM/CSIC) [AMS-02 Collaboration] Indirect Searches for Gravitino Dark Matter [IceCube Collaboration] PLANCK 202 30 May 202 6 / 5
Indirect Detection of Gravitino Dark Matter Gravitino Decay Signals in Cosmic-Ray Spectra T 3 Antiproton FluxGeV 2 m 2 s sr 00 0 0. 0.0 0 3 antiproton flux background PAMELA AMS0 IMAX Τ32 0 27 s m32 00 GeV TeV 0 TeV 0 00 000 0 000 Kinetic EnergyGeV CAPRICE98 CAPRICE94 MASS9 BESSPolar II BESSPolar BESS 00 BESS 99 BESS 98 BESS 9597 E 2 GammaRay FluxGeV m 2 s sr 0.03 0.0 0.003 0.00 0.0003 0.000 isotropic diffuse gamma-ray flux Τ32 0 27 s m32 00 GeV TeV 0 TeV 0. 0 00 000 0 000 EnergyGeV Observed antiproton spectrum well described by astrophysical background No need for contribution from dark matter Isotropic diffuse gamma-ray spectrum exhibits power-law behaviour Fermi LAT EGRETStrong et al. EGRETSreekumar et al. Source not completely understood, but no sign of spectral features of a particle decay Even without astrophysical backgrounds lifetimes below O(0 26 0 27 ) s excluded Gravitino decay cannot be the origin of the PAMELA and Fermi LAT cosmic-ray anomalies Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 7 / 5
Indirect Detection of Gravitino Dark Matter Gravitino Decay Signals in Cosmic-Ray Spectra T 3 Antiproton FluxGeV 2 m 2 s sr 00 0 0. 0.0 0 3 antiproton flux background PAMELA AMS0 IMAX Τ32 0 27 s m32 00 GeV TeV 0 TeV 0 00 000 0 000 Kinetic EnergyGeV CAPRICE98 CAPRICE94 MASS9 BESSPolar II BESSPolar BESS 00 BESS 99 BESS 98 BESS 9597 E 2 GammaRay FluxGeV m 2 s sr 0.03 0.0 0.003 0.00 0.0003 0.000 isotropic diffuse gamma-ray flux Τ32 0 27 s m32 00 GeV TeV 0 TeV 0. 0 00 000 0 000 EnergyGeV Observed antiproton spectrum well described by astrophysical background No need for contribution from dark matter Isotropic diffuse gamma-ray spectrum exhibits power-law behaviour Fermi LAT EGRETStrong et al. EGRETSreekumar et al. Source not completely understood, but no sign of spectral features of a particle decay Even without astrophysical backgrounds lifetimes below O(0 26 0 27 ) s excluded Gravitino decay cannot be the origin of the PAMELA and Fermi LAT cosmic-ray anomalies Astrophysical sources like pulsars required to explain cosmic-ray excesses! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 7 / 5
Indirect Detection of Gravitino Dark Matter Antideuteron Signals from Gravitino Decays In particular sensitive at low energies due to small astrophysical background AMS-02 and GAPS will be able to put strong constraints on light gravitinos TnAntideuteron Fluxm 2 s sr 0 4 0 5 0 6 0 7 0 8 0 9 0 0 BESS 9700 ΦF 500 MV GAPSULDB GAPSLDB AMS02 AMS02 background Τ32 0 27 s m32 00 GeV TeV 0 TeV 0. 0 00 000 Kinetic Energy per NucleonGeVn Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 8 / 5
Indirect Detection of Gravitino Dark Matter Antideuteron Signals from Gravitino Decays In particular sensitive at low energies due to small astrophysical background AMS-02 and GAPS will be able to put strong constraints on light gravitinos TnAntideuteron Fluxm 2 s sr 0 4 0 5 0 6 0 7 0 8 0 9 0 0 BESS 9700 ΦF 500 MV GAPSULDB GAPSLDB AMS02 AMS02 background Τ32 0 27 s m32 00 GeV TeV 0 TeV 0. 0 00 000 Kinetic Energy per NucleonGeVn Antideuterons are a valuable channel for light gravitino searches! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 8 / 5
Indirect Detection of Gravitino Dark Matter Neutrino Signals from Gravitino Decays Neutrinos provide directional information like gamma rays Gravitino signal features neutrino line at the end of the spectrum Atmospheric neutrinos are the dominant background for the gravitino signal Discrimination of neutrino flavours would allow to reduce the background Signal-to-background ratio best at the end of the spectrum and for large gravitino masses E 2 Neutrino FluxGeV m 2 s sr 0 3 00 0 0. 0.0 0 3 0 4 Τ32 0 26 s ΝΤ ΝΜ Νe m32 00 GeV TeV 0 TeV 0 00 000 0 000 00 000 EnergyGeV IceCube40 UnfoldingΝΜ IceCube40ΝΜ AMANDAII UnfoldingΝΜ AMANDAII ForwardΝΜ SuperKamiokandeΝΜ FréjusΝΜ FréjusΝe Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 9 / 5
Indirect Detection of Gravitino Dark Matter Neutrino Signals from Gravitino Decays Neutrinos provide directional information like gamma rays Gravitino signal features neutrino line at the end of the spectrum Atmospheric neutrinos are the dominant background for the gravitino signal Discrimination of neutrino flavours would allow to reduce the background Signal-to-background ratio best at the end of the spectrum and for large gravitino masses E 2 Neutrino FluxGeV m 2 s sr 0 3 00 0 0. 0.0 0 3 0 4 Τ32 0 26 s ΝΤ ΝΜ Νe m32 00 GeV TeV 0 TeV 0 00 000 0 000 00 000 EnergyGeV IceCube40 UnfoldingΝΜ IceCube40ΝΜ AMANDAII UnfoldingΝΜ AMANDAII ForwardΝΜ SuperKamiokandeΝΜ FréjusΝΜ FréjusΝe Neutrinos are a valuable channel for heavy gravitino searches! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 9 / 5
Indirect Detection of Gravitino Dark Matter Neutrino Detection with Upward Through-Going Muons Muon tracks from charged current DIS of muon neutrinos off nuclei outside the detector Advantages Muon track reconstruction is well-understood at neutrino telescopes Disadvantages Neutrino nucleon DIS and propagation energy losses shift muon spectrum to lower energies Bad energy resolution (0.3 in log 0 E) smears out cut-off energy Muon Fluxkm 2 yr 0 5 0 4 0 3 00 0 0. Upward ThroughGoing Muons 0 atmospheric background Statistical Significance 0. m32 00 GeV TeV 0 TeV 0.0 Τ32 0 26 s 0 00 000 0000 00000 EnergyGeV Upward ThroughGoingMuons Τ32 0 26 s m32 00 GeV TeV 0 TeV 0 00 000 0000 00000 EnergyGeV Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 0 / 5
Indirect Detection of Gravitino Dark Matter Neutrino Detection Improvements Using Showers Hadronic and electromagnetic showers from charged current DIS of electron and tau neutrinos and neutral current interactions of all neutrino flavours inside the detector Disadvantages TeV-scale showers are difficult to discriminate from short muon tracks Advantages 3 larger signal and 3 lower background compared to other channels Better energy resolution (0.8 in log 0 E) helps to distinguish spectral features 0 6 Shower Events 00 Shower Events Shower Ratekm 3 yr 0 5 0 4 0 3 00 0 atmospheric background Τ32 0 26 s m32 00 GeV TeV 0 TeV 0 00 000 0000 00000 EnergyGeV Statistical Significance 0 0. 0.0 Τ32 0 26 s m32 00 GeV TeV 0 TeV 0 00 000 0000 00000 EnergyGeV Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 / 5
Indirect Detection of Gravitino Dark Matter Neutrino Detection Improvements Using Showers Hadronic and electromagnetic showers from charged current DIS of electron and tau neutrinos and neutral current interactions of all neutrino flavours inside the detector Disadvantages TeV-scale showers are difficult to discriminate from short muon tracks Advantages 3 larger signal and 3 lower background compared to other channels Better energy resolution (0.8 in log 0 E) helps to distinguish spectral features 0 6 Shower Events 00 Shower Events Shower Ratekm 3 yr 0 5 atmospheric background 0 4 0 3 00 0 Τ32 0 26 s m32 00 GeV TeV 0 TeV 0 00 000 0000 00000 EnergyGeV Statistical Significance 0 0. Τ32 0 26 s 0.0 m32 00 GeV TeV 0 TeV 0 00 000 0000 00000 EnergyGeV Showers are potentially the best channel for dark matter searches in neutrinos! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 / 5
Indirect Detection of Gravitino Dark Matter Limits on the Gravitino Lifetime Gravitino Lifetimes 0 29 0 28 0 27 0 26 0 25 0 24 excluded by line searches excluded by diffuse flux 0 00 000 0 000 Gravitino MassGeV Fermi LAT photon line Vertongen et al. photon line Fermi LAT diffuse flux Cosmic-ray data give bounds on gravitino lifetime Photon line bounds very strong for low gravitino masses Uncertainties from charged cosmic-ray propagation Background subtraction will improve bounds Antideuterons can be complementary to photon line searches for low gravitino masses Neutrino bounds are competitive for heavy gravitinos Gravitino Lifetimes 0 28 0 27 0 26 0 25 0 24 antideuteron sensitivity excluded by electronpositron flux excluded by antiproton flux excluded by positron fraction 00 000 0 000 Gravitino Lifetimes 0 27 0 26 0 25 0 24 Gravitino MassGeV Fermi LATH.E.S.S. e e PAMELA p exclusion from PAMELA e e e throughgoing muons after year at IceCubeDeepCore 00 000 0 000 Gravitino MassGeV Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 2 / 5
Indirect Detection of Gravitino Dark Matter Limits on the Gravitino Lifetime Gravitino Lifetimes 0 29 0 28 0 27 0 26 0 25 0 24 excluded by line searches excluded by diffuse flux 0 00 000 0 000 Gravitino MassGeV Fermi LAT photon line Vertongen et al. photon line Fermi LAT diffuse flux Cosmic-ray data give bounds on gravitino lifetime Photon line bounds very strong for low gravitino masses Uncertainties from charged cosmic-ray propagation Background subtraction will improve bounds Antideuterons can be complementary to photon line searches for low gravitino masses Neutrino bounds are competitive for heavy gravitinos Wide range of bounds from multi-messenger approach! Gravitino Lifetimes 0 28 0 27 0 26 0 25 0 24 antideuteron sensitivity excluded by electronpositron flux excluded by antiproton flux excluded by positron fraction 00 000 0 000 Gravitino Lifetimes 0 27 0 26 0 25 0 24 Gravitino MassGeV Fermi LATH.E.S.S. e e PAMELA p exclusion from PAMELA e e e throughgoing muons after year at IceCubeDeepCore 00 000 0 000 Gravitino MassGeV Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 3 / 5
Indirect Detection of Gravitino Dark Matter Limits on the Amount of R-Parity Violation Limits on gravitino lifetime constrain the strength of R-parity violation: τ 3/2 Gamma-ray bounds are important for all gravitino masses Bounds from all cosmic-ray channels are comparable in strength Neutrino bounds competitive especially for large masses M2 Pl ξ 2 m 3 3/2 0 7 Ξ 0 7 RParity Violating ParameterΞ 0 8 0 9 0 0 0 0 2 Fermi LAT Γ line Fermi LAT diffuse Γ PAMELA p GAPSAMS02 d prospects SuperKamiokandeΝΜ IceCube ΝΜ prospects Ξ 0 0 00 000 0 000 Gravitino MassGeV Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 4 / 5
Indirect Detection of Gravitino Dark Matter Limits on the Amount of R-Parity Violation Limits on gravitino lifetime constrain the strength of R-parity violation: τ 3/2 Gamma-ray bounds are important for all gravitino masses Bounds from all cosmic-ray channels are comparable in strength Neutrino bounds competitive especially for large masses M2 Pl ξ 2 m 3 3/2 0 7 Ξ 0 7 RParity Violating ParameterΞ 0 8 0 9 0 0 0 0 2 Fermi LAT Γ line Fermi LAT diffuse Γ PAMELA p GAPSAMS02 d prospects SuperKamiokandeΝΜ IceCube ΝΜ prospects Ξ 0 0 00 000 0 000 Gravitino MassGeV Indirect searches reach the cosmologically favoured range of R-parity violation! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 4 / 5
Conclusions and Outlook Conclusions and Outlook Gravitino dark matter with broken R parity is well motivated from cosmology The Gravitino lifetime is naturally in the range of indirect detection experiments Cannot explain the PAMELA and Fermi LAT anomalies due to constraints from gamma rays and antiprotons Forthcoming antideuteron searches will probe light gravitino dark matter Neutrino experiments like IceCube can probe heavy gravitino dark matter New detection strategies will improve the sensitivity of neutrino experiments to dark matter Multi-messenger approach allows to constrain gravitino lifetime and strength of R-parity violation over a wide range of gravitino masses Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 5 / 5
Conclusions and Outlook Conclusions and Outlook Gravitino dark matter with broken R parity is well motivated from cosmology The Gravitino lifetime is naturally in the range of indirect detection experiments Cannot explain the PAMELA and Fermi LAT anomalies due to constraints from gamma rays and antiprotons Forthcoming antideuteron searches will probe light gravitino dark matter Neutrino experiments like IceCube can probe heavy gravitino dark matter New detection strategies will improve the sensitivity of neutrino experiments to dark matter Multi-messenger approach allows to constrain gravitino lifetime and strength of R-parity violation over a wide range of gravitino masses Thanks for your attention! Michael Grefe (IFT UAM/CSIC) Indirect Searches for Gravitino Dark Matter PLANCK 202 30 May 202 5 / 5