Novel neutrino interactions at IceCube

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1 Novel neutrino interactions at IceCube Alex Friedland Los Alamos Dec 17,

2 Collaborators JJ Cherry postdoc, Los Alamos Ian Shoemaker postdoc, Los Alamos -> CP3, Denmark 2

3 Generalities: new physics searches and neutrinos I d like to pick up on a point made yesterday by Heather Ray We don t understand where new physics is hiding -> cast a wide net! LHC Dark matter searches (direct, indirect) Axion searches (ADMX, CAST, etc) Precision low-energy stuff Electric dipole moments, rare decays, Kaon mixing... Cosmological fits Neutrino sector? 3

4 Why think about neutrinos? Because the neutrino sector has been getting some amazing data over the last two decades There was something new almost every year! Because this is where we have already discovered physics beyond the standard model (oscillations) Leptonic flavor mixing results greatly surprising for model-builders See talk by Pierre Ramond from yesterday Because in the next years, we should expect more precision data 4

5 PDG

For comparison, around the same time... hep-ph/ 9810316 (TASI lectures by J. Hewlett) Fig. 18 M W (GeV/c 2 ) 80.6 80.5 80.4 80.

6 For comparison, around the same time... hep-ph/ (TASI lectures by J. Hewlett) Fig. 18 M W (GeV/c 2 ) INDIRECT LEP + SLC World Av. Higgs Mass (GeV/c 2 ) M top (GeV/c 2 ) 6

categories: New interactions ( NSI ) New states ( sterile

7 What else could be hiding in the neutrino sector? Generally speaking, ideas in the literature fall into two categories: New interactions ( NSI ) New states ( sterile neutrinos ) Both of these ideas have decades of theoretical work behind them 7

8 New neutrino-matter interactions Could appear at oscillation experiments, for example: NSI Solar neutrino survival probability pep Std. MSW Atmospheric neutrino oscillations Neutrino beams NO A, e 0.4, 0 Non-oscillation experiments, for example P e LHC, Tevatron P e 8

9 Here, I wish to speculate about neutrino selfinteractions That s the hardest of them all to constrain Scattering neutrino beams is not easily accomplished On the other hand, in the universe this experiment does happen over and over. Hence, this interaction could have profound astrophysical and cosmological implications For example, it is responsible for collective flavor oscillations in supernova environments Neutrino free-streaming in the early universe Neutrino-dark matter interactions? 9

10 Volume 32B. number 2 PHYSICS LETTERS 8 June 1970 ON THE v - v INTERACTION Do Yu. BARDIN, S. M. BILENKY, B. PONTECORVO Joint Institute for Nuclear Research, Dubna, USSR Received 28 April 1970 A new hypothetical interaction between neutrinos is considered. It is shown that even relatively strong v e - v e, vtz - v/. t and Pe - vtl interactions are not in contradiction with existing data and upper limits for the corresponding interaction constant are obtained. New experiments are suggested which might give information on ~, - v interactions. Bardin, Bilenky, Pontecorvo (1970) Barger, Keung, Pakvasa (1982) Manohar (1987) Kolb & Turner (1987) C.L. Fuller, Mayle, Wilson (1988) Bilenky, Bilenky, Santamaria (1993)... 10

We propose to test this interaction at IceCube Beam: ultra-high energy neutrinos, originating at cosmological distances (z~1-4) in astrophysical sources such as GRBs or AGNs Target: cosmic neutrino

11 We propose to test this interaction at IceCube Beam: ultra-high energy neutrinos, originating at cosmological distances (z~1-4) in astrophysical sources such as GRBs or AGNs Target: cosmic neutrino background, 336 cm -3 at the current epoch Detector: IceCube A large-volume Cherenkov detector made of 5160 photomultipliers (PMTs) at depths between 1450 and 2450 m in natural Antarctic ice From IceCube, Science 342, (2013) 11

We propose to test this interaction at IceCube IceCube reported 28 events with energies between 20 TeV and 2 PeV that stand above the atmospheric

12 We propose to test this interaction at IceCube IceCube reported 28 events with energies between 20 TeV and 2 PeV that stand above the atmospheric background (4 sigma) 10 2 A Science 342, (2013) Two PeV events are affectionately named Bert and Ernie Events per 662 days Phys. Rev. Lett. 111, (2013) 10-1 The third one, at 2 PeV, is in the pipeline ( Big Bird ) Some features of this data could be pointing to the presence of new interactions (our speculation!) Deposited EM-equivalent energy in detector (TeV) From IceCube, Science 342, (2013) 12

13 Peculiarity of the data The observed spectrum lines up with E -2 expectation from astrophysics, except that there are no events above ~ 2 PeV (one would expect 3-6 in the 2-10 PeV window from a continuing E -2 spectrum) no events in the gap between 0.3 and 1 PeV relative paucity of muon events (none at PeV, one reported between 0.15 to 0.3 PeV) Leptoquarks at the detection point? Barger, Keung, arxiv: Oscillations of pseudo-dirac neutrinos with Δm 2 ~10-15 ev 2 Joshipura, Mohanty, Pakvasa, arxiv:

Our speculation We propose that something happens in propagation, but not an oscillation! What if the universe is not transparent to neutrinos at certain energies (~PeV)?

14 Our speculation We propose that something happens in propagation, but not an oscillation! What if the universe is not transparent to neutrinos at certain energies (~PeV)? That s a crazy thing to say, because it is well known that the universe is transparent to neutrinos with energies below ~10 22 ev At those ~10 22 ev, the neutrinos finally get scattered/absorbed because of the s-channel Z-boson resonance T. Weiler, PRL 1982 P. Gondolo, G. Ge/mini / Cosmic neutrinos II I I 10 ~ - -\ N Cs - Cl) -~ 4- N N 5 N 2 2\ - scattering ~ annihilatio \ H Hi H H III log E~ [TeV] Gondolo, Gelmini, 1993 E c.m. p (10 1 ev)(10 23 ev) 10 2 GeV m Z 14

15 Our speculation The standard transparency conclusion is based on standard physics only What if we have a light mediator particle? resonant condition m 2 = s 2m E =) m p (10 1 ev)(10 15 ev) 10 7 ev Dark force Could be a vector or scalar 15

16 Some rough estimates Resonant cross section is bigger than that on the Z pole, since ɸ is lighter res (#)m 2 (#)10 24 cm 2 Given relic neutrino number density ~ 10 3 (we assume astrophysical sources at z of several), we can (first very roughly) estimate that intersting (l n) 1 (Gpc 10 3 cm 3 ) cm 2 Therefore, there is plenty of room for the numerical coefficient in the cross section formula to be small (due to small coupling and/or small mixing) Also, there is room for the redshift effects to work (see later) 16

17 Framework How to get such new interaction into the neutrino sector? We don t want to build specific models here, just outline a framework We don t want to break the weak SU(2) And we don t have to. It is well-known that our standard neutrinos could oscillate into a sterile state. Let s give that state new interactions Then our familiar 3 light neutrino mass eigenstates would acquire new interaction thanks to the mixing with the new state The amount of mixing could be different for each of the states, hence rich phenomenological possibilities + a state that is predominately sterile 17

18 Framework A new fermion in the dark sector, which couples via a ɸ-mediated interaction. The only way this state interacts with the Standard Model is via mixing with neutrinos. Neutrino Portal The dark sector has its own Higgs mechanism with a field L LH R + D R + M R R that gives ɸ its mass Simple renormalizable see-saw Lagrangian. Upon integrating out the heavy righthanded, one gets a light sterile mixing with the usual active neutrinos in R D L Akin to baryonic neutrino in Pospelov, arxiv: , only we don t want the hidden gauge group to directly couple to the SM baryon number (which could induce large NSI) 18

19 Constrains? Schematically: Laboratory constraints, a la Pontecorvo, are completely avoided! µ Neutrinos in laboratory are produced as flavor states, don t have the νd component. For example, processes of the type considered by Laha, Dasgupta & Beacom, arxiv: (a la Barger et al 1982) don t occur in the detector K s ū f K W V µ In dense environments such as supernova, large matter potential reduces the admixture of the sterile state -- details beyond the scope of this talk 19

20 Resonant absorption As neutrinos oscillate in vacuum, however, they go into mass eigenstates and gain the new interaction Applies to both beam UHE neutrinos and the cosmic neutrino background Neutrinos could scatter resonantly when the energies are right The resonance condition is determined by the absolute neutrino masses, which could in principle leave imprints in the spectrum cf Eberle, Ringwald, Song, Weiler, hep-ph/ in the standard case (which requires however neutrinos of > ev) 20

21 s-channel: A few physics considerations Breit-Wigner BW 12 m 2 in out 4(s m 2 )+ 2 tot! res 12 m 2 in tot 12 m 2 sin4 cross section on resonance dependents on the new mixing angle θ the width Γtot depends on the coupling g of the sterile neutrino to the dark force φ As the universe expands, the resonance line sweeps through the spectrum The net effect then depends on the distribution of astrophysical sources (GRBs) with z 21

22 Example calculation Sources are GBRs (Waxman- Bahcall) + AGNs at high E 22

Discussion of the results The plot shows four absorption bands, with the one at highest energies broadened by thermal motion of the lightest neutrinos Assumed normal mass hierarchy + 1 ev

23 Discussion of the results The plot shows four absorption bands, with the one at highest energies broadened by thermal motion of the lightest neutrinos Assumed normal mass hierarchy + 1 ev sterile state Assumed that the lightest neutrino is still relativistic at T ~ 1.9 K Assumed equal sterile mixing with all light states assumed for illustration Assume mφ=10 MeV for the mediator mass 23

24 Discussion of the results Notice the width of the absorption band between 0.3 and 1 TeV. This is where IceCube sees no events Lower energy events Gap Bert, Ernie,Big Bird This width is obtained automatically, as a consequence of the distribution of GRBs with redshift! The absorption line sweeps through that part of the spectrum as the universe expands Atmospheric BG Hi energy cutoff 24

25 t-channel scattering Notice also that some of the curves show decay with energy Effect of the t-channel scattering t-channel depends on g 4 sin 4 θ, which is different from t- channel Depending on the choice of parameters, one can have domination by s-channel (bands), t-channel (continuum), or both 25

26 Selective absorption possible Amounts of sterile mixing to different mass eigenstates could be different. This has observable consequences. Example: Imagine we have our sterile state mixing mostly with ν3. If that state is absorbed as a result, ν1 and ν2 still make it to Earth. In this scenario, with more data, IceCube would fill in some events in the gap between 0.3 and 1 TeV, but there would still be a dip 26

27 Selective absorption: flavor effects In the standard case, the prediction is to have equal numbers of flavors at the detector. That s because the muon neutrino projects equally onto the three mass eigenstates. Imagine we have our sterile state mixing mostly with ν3. If that state is absorbed as a result, the resulting flavor composition on earth will be different. Because ν3 has almost no electron neutrino component (suppressed by theta13), the observed flux would have more electron neutrinos than muon. More blobs vs tracks 27

28 Broad range of physical options In general, one can vary: Different mixing angles and couplings Overall mass scale of light neutrinos Mass hierarchy Cosmological abundance of sterile neutrinos ( generally modeldependent) It could be a theorist s dream...and an experimentalist s nightmare! 28

29 Possible cosmological implications If the sterile neutrino is also coupled to dark matter, a whole host of possibilities open up Recently, it was suggested that neutrino-dark matter coupling could solve the missing satellites/too-big-to-fail problems with structure van den Aarssen, Bringmann, Pfrommer, PRL 2012 It was separately proposed that dark matter self-interactions could alleviate problems with cores vs cusps. Loeb & Weiner, PRL 2011 Mediator masses in the 10 MeV range are optimal Our framework easily and naturally accommodates neutrino-dark matter coupling that would impact both the cutoff halo sizes and the core profiles 29

30 Conclusions Neutrino sector could still contain many surprises The universe could be opaque to neutrinos in certain energy ranges. This can be easily achieved in a framework combining the ideas of sterile neutrinos and nonstandard interactions. The IceCube experiment could be probing this physics. The range of physical scenarios is broad. This could turn into an experimentalist s nightmare. On the other hand, there is a possibility that the IceCube is probing a portal into the dark sector! 30

Neutrino Physics: an Introduction

Neutrino Physics: an Introduction Lecture 3: Neutrinos in astrophysics and cosmology Amol Dighe Department of Theoretical Physics Tata Institute of Fundamental Research, Mumbai SERC EHEP School 2017 NISER