j. pradler and m.pospelov , to appear ~ next weak

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GeV scale metastable particles and BBNor

Unintended benefit of metastableGeV particles: reduction of Li overabundance

Maxim PospelovUniversity of Victoria and Perimeter Institute

 J. Pradler and M.Pospelov, to appear ~ next weak

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Outline of the talk

1. Introduction and Motivation. New look at GeV scale phenomenology.

2. Current status of BBN. 7Li is “over-predicted”. A multitude of solutions.

3. Decay of GeV scale particles: injection of pions, kaons, muons etc. Easy to fix Li with lifetimes 200-10000 seconds

4. WIMP model realisations: Secluded U(1) with metastable Higgses.

5. Super-WIMP realisations. 6. Conclusions.

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“Revival” of new physics at (sub)-GeV scale1. May help to solve some puzzles in low energy data

(discrepancy in g-2 of muon, HyperCP events, possibly anomalous events in “neutrino factories” )

2. May lead to novel phenomena if used as mediators between WIMP dark matter and Standard Model. (In particular can explain PAMELA and FGST excess of lepton cosmic rays, Arkani-Hamed et al. 2008, MP and Ritz 2008)

3. Could be searched for at the “luminosity frontier” : e.g. colliders, fixed targets etc (~20% of workshop participants worked on it: Itay, Natalia, many others ... )

4. Have some natural field theory realizations: kineticly mixed U(1) – (Holdom 1986); GeV-scale RH neutrinos, singlet scalars...

In this talk, I will investigate influence of metastable GeV scale particles on the outcome of primordial nucleosynthesis. I will be loosely provocative (suggestion of D. Kaplan) and speculate on 7Li

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BBN abundances at ´WMAP

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Status of standard BBN with CMB input

Coc et al, ApJ 2005

“Lithium problem”!!

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9Be vs metallicityThere is no evidence for primordial plateau

SBBN models predicts 9Be ~ 10-18

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6Li is detected in a handful of starsA lot of speculations about primordial 6Li!

Unexpected plateau (?) of 6Li with metallicity (Asplund et al., 2005);

Claim is challenged in Cayrel et al, 2007.

6Li/H ~ 10-11

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More on 7Li generation during the BBNIn fact, it is 7Li+7Be that we are interested in (much later, 7Be

captures an electron and becomes 7Li). Things are simple: there is one reaction in, and one reaction out

3He+ ! 7Be + - IN. 7Be +n ! p +7Li – OUT, (followed by 7Li+p ! 2)At T>25 keV, 7Li is unstable being efficiently burned by protons. 4He, 3He, D, p, and n can be all considered as an input for lithium

calculation. 1. 3He and n abundances ? All reactions are too well-known. 3He is

indirectly measured by the solar neutrino flux. 2. 3He(, )7Be reaction is now known with better than 10%

accuracy.New ways of destroying 7Be ?

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Ways the 7Li problem can be resolved Astrophysical: Extra depletion of lithium along Spite plateau Nuclear: SBBN prediction is somehow not correct (MP, Cyburt:

suggestion of a resonant enhancement of 7Be(D,p)8Be reaction. Unlikely last hope…)

Cosmological: 7Li is measured locally, while D and baryon-to-photon ratio globally. If baryon density fluctuates on sub-horison to CMB scales, one could “place” Milky Way in the baryon-underdense region. Slight variation in D binding can deplete 7Li (scalar-tensor theories)

Particle physics: Decays/annihilations of heavy relics can reduce 7Li.

7Li can also be destroyed in catalyzed reactions.

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BBN with energy injectionEffect of the “baryonic” energy injection

(Dimopoulos et al.; Reno and Seckel, 1980s. )

Neutron-reachenergy injection at t~500 sec is capableof reducing 7Li by ~2(Reno and SeckelK. Jedamzik).D/H is higher About 10-5 extra neutrons needto be injected to get an appreciable reduction of lithium.

Secondary production of 6Li

Non-equilibrium BBN: synthesis of A=6,9,10 elements in secondary and tertiary collisions

Secondary processes: Hadronic energy injection leads to spallation on 4He, creating energetic A=3 nuclei. A=6 will form:

Dimopoulos, Starkman et al., 80s Below 5 keV, efficiency ~10-3

Tertiary processes: Emerging 6He and 6Li are energetic and will further collide with 4He in the plasma forming 9Be with similar

efficiency, MP Pradler 2010. The early time energy injection (T~20 keV) would result in the enhancement of 9Be/6Li.

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What was known:1. WIMP DM annihilation cannot solve 7Li problem. Not enough

neutrons; too much of 6Li is generated as colateral damage.2. One could “get rid” of 7Li excess using decays of EW scale relics

with ~ some baryons/antibaryons in the final states.3. None of the secluded models with light mediators (e.g. tuned to

fit PAMELA) is suitable for that because (anti)-nucleons in the final states are either absent or suppressed.

What we found:4. If some particles from GeV sector are metastable (100-1000s),

and decay producing pions/kaons or muons - 7Li can be suppressed while other BBN predictions are not worsened.

5. There are different classes of models that easily fit this requirement. Including the most popular “light U(1)” of Holdom-type.

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General pictureWe assume some (sub)-GeV scale neutral relics X with appropriate lifetime (that cannot decay to nucleons) and consider X! p+p-X! K+, K- and KL, KS

X ! Muons ! electron antineutrinos

Main calculation : meson-induced p ! n conversion with ensuing change to the BBN network. (Requires proper treatment of EM stopping of particles, meson-nucleon and meson-helium reactions at-rest and in-flight (delta resonance!), spectrum of energetic A=3 nuclei etc. Overall, not an easy problem.)

How many pions, kaons etc and with what injection rates (determined by lifetime of X) are required in order to ensure 7Li in the interval (1--2.5) £ 10-10 ?

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Estimates of p! n efficiency How many pions do we need ? = what is the probability of producing

a neutron within pion lifetime?Proton capture rate by p-

Probability is small

But not too small, given that we need 10-5 extra neutrons per proton. Therefore about ~10 pions per proton injected around T=40 keV will

do the job. Kaon case is similar. O(1) K- per proton is enough.

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7Li reduction from pion injection at threshold

Wide range of lifetimes is suitable (much wider than for EW relics)

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Time evolution of abundances in pBBN

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mBBN or nBBNHow many muons (source of antineutrinos) do we need?Rate for proton-induced conversion of neutrino to neutron is smaller

than Hubble rate by about nine orders of magnitude

O(104) muons per proton is required.

“Easy to arrange”

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mBBN or nBBN

Extra region at lifetime ~3hr. Energy injection corrects D/H back to SBBN

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Model ConnectionsTwo types: “WIMPs” – initially very abundant (e.g. as photons) – then deplete

themselves at T~m, and in our case decay after 100-104 sec.“super-WIMPs” – initially not present at all – get generated by

thermal leakage of SM, then decay. Vector portal model: Ã will be considered in this talk

Higgs portal model:

WIMP or Super-WIMP depends on strength of couplings

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Vector portal model in WIMP regime

Long-lived particle – Higgs’ boson, if mh’ < mV (SUSY mass pattern) Decay rate ~ (mixing angle)^4.

In contrast, Vector particle decays in a picosecond.

Perfect candidate – provided that one can somehow reduce its abundance to an acceptable level.

(For a long time I thought that lifetimes > second should be excluded by over-closure of the Universe at the time of the BBN. Not so. I acknowledge a conversation with N. Weiner.)

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Cosmological abundance of secluded Higgses Initial abundance of h’ is thermal. They live ~ 1000 seconds, and

cannot annihilate very efficiently. Naively, they should overclose the Universe at ~ 1 second, and such models are ruled out.

However, “co-decay” processes save the day:

where . The last process is the most efficient. kappa » 3 £ 10-5 is required for the right lifetime range. 2 m¹ < mh < 2 m¼ and mV = 1.7 mh solves lithium problem via

injection of muons.mh > 2 m¼ and mV = 1.3 mh solves lithium problem via injection of

pions (kaons).

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Super-WIMP regimeTake coupling effective coupling constant(k)2® = 10-26

Then vector lives 1000 sec. Model has almost no free parameters. – And it works!

Vectors do not exist initially, then get thermally produced at the level O(1) per baryon, and then decay after 1000 sec or so. Straight calculation of abundance (well... assuming massless quarks):

MV ~ 700 MeV reduces lithium rather efficiently because of the large branching to pions and Ep ~ delta resonance.

I see no other probes of this model except BBN.

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Conclusions

Lithium is discrepant by a factor 3-5. Nobody really knows why.

Particle physics looks as an attractive yet speculative possibility of curing Li problem. Injection of not-so-energetic mesons can easily solve the problem, provided that there are at least O(1) exotic GeV scale particles sourcing these mesons.

Minimalistic models of different kinds can provide such particles. In particular, GeV-scale U(1) is a natural candidate because of the accidental longevity of the Higgs’.

And it “works” – correct cosmological abundances can be easily obtained with moderate splitting between h and V.

Lots of other experimental signatures that I have no time to talk about.

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BBN with energy injectionannihilating dark matter

Thermal WIMP

benchmark

Relatively easy to create 6Li, difficult to get rid of 7Li

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Burning of 7Be using deuteriumIt has been suggested (Coc et al., 2004) that if the reaction rate of

7Be(d,p)®® is arbitrarily increased by a factor of ~ 100, the lithium problem can be “solved” right during the BBN.

Subsequent experimental search (Angulo et al., 2005) have shown no enhancement in this reaction.

It is important, however, that the search was made at E~400 keV, and the extrapolation to BBN regime was done assuming smoothness of astrophysical S-factor (cross section).

Such assumptions can be spectacularly violated by the presence of near threshold resonances ( e.g. F. Hoyle, 1950s).

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9B energy levels

from TUNL

nuclear data

project

Zooming in: 16.7 MeV resonance near 7Be +d

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Nothing much is known about 5/2+, 16.7 MeV +/- 100 keV resonance in 9B. Information about mirror nucleus, 9Be, shows that this resonance is extremely narrow.

We (R. Cyburt and MP) try to determine parameters of this resonance phenomenologically, and then see if it can be consistent with nuclear physics/quantum mechanics.

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Parameters of the resonance

Above the black line, 7Li/H < 0.5 [7Li/H]SBBN,and the Lithium problem is “solved”. One needs a resonance

in 160-200 keV range, and Gamma > 10 keV.

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Uncertainty in 7Li due to 9B resonance

¡ ~10 keV is a problem because of the Coulomb screening. Such a large deuterium separation width at a resonance energy of 200 keV implies extremely large radius for the 7Be+d interaction channel, as large as 10 fm. This is border-line of what is allowed by QM.

If indeed lithium problem is solved that way, it implies “new nuclear physics”, i.e. 16.7 MeV resonance in 9B is a 10 fm-size bound state of 7Li and Deuteron. Outrageously large size!

Being completely agnostic about properties of this resonance within QM, we arrive at the the following prediction for primordial lithium

Results of injecting extra neutrons

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Lithium can be reduced while D kept within bounds if extra neutrons are injected early on (T~40 keV). Secondary and tertiary processes will result in 6Li and 9Be in such scenario.

Non-equilibrium synthesis of 9Be is an important question to be addressed!

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Possible astrophysical resolution of 7Li discrepancy

There is a growing suspicion that pop II stars can themselves deplete lithium by admixing it from the atmospheres into a hot interrior where it gets destroyed (Korn et al., 2006, employs diffusion and extra mixing).

Can it provide a factor of 2-3 suppression? Can the suppression work uniformly along the Spite plateau,

without introducing extra scatter? Would the measured abundances of other elements be OK?

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Nonstandard BBN scenariosLate injection of electromagnetic/hadronic energy distorts primordial

abundances, especially for those elements where the SBBN processes are extremely inefficient

(4He(d,°)6Li is the radiative E2 reaction, suppressed by 8 orders of magnitude relative to “normal” reactions)

Energy injection with baryons in the final stay allows to circumvent this by a chain of endo-thermic but photonless reactions (Dimopoulos et al, 1980s) 4He + p 3H + p + p, Q=-16 MeV

There is a possibility of suppressing 7Be if O(10-5) neutrons per proton are injected (Jedamzik, 2004). This also increases D/H. Typical lifetime ~ 1000 sec is required.

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BBN with energy injectionannihilating dark matter

Thermal WIMP

benchmark