IFAE06: new physics without new physics

Transcription

1 IFAE06: new physics without new physics Hopefully for the last time, re-review motivations and expectations for LHC. 0) LHC book says: find the Higgs. But no Higgs = new physics no new physics = only the Higgs 1) Understand why the weak scale is much below the Planck scale. 2) Partially test if dark matter as thermal relic. The main interest of LHC is that we do not know what it will find.

2 The LHC inverse problem? Theoretical activity is shifting to: being ready for LHC This is to be done, but constructive BSM work and fun will likely start with LHC LHC might not fully fix new physics, we should try global fits as well known in data-rich fields: tan 2 Θ m 2 in ev In 1984 we were ready enough for SpS. In 2006 we are too much ready for LHC. Maltoni: madgraph.hep.uiuc.edu

3 Thermal dark matter

4 Cosmic inventory Total density = critical density Present composition: Dark energy (maybe cosmo-illogical constant) % Dark matter (maybe new neutral stable particle) % Known particles (γ, e, ν, p, Helium, Deuterium... ) %

5 Dark Matter Ω DM 22%, neutral, non-baryonic Almost all particle abundances understood assuming that they are thermal relics. Assuming that this holds for DM fixes: M DM /g DM T now M Pl TeV Range not fully covered by LHC. Missing energy signals. DM usually hoped to be a byproduct of the hierarchy problem: many solutions have DM candidates, kept stable by theorists that impose Z 2 -like symmetries (R-parity, T -parity, KK-parity...), that also split old from new physics, hiding it. Implication for LHC: pair production. Good models have similar collider phenomenologies

6 The hierarchy problem

7 Main questions Around 1970 theorists anticipated the SM thanks to gauge invariance. To proceed further with BSM a different guideline was adopted: naturalness. Maybe it is the right direction, maybe not. In the past, naturalness problems signaled new physics: Problem Natural solution? New physics δm e = αλ Yes: chiral symmetry positron δ(m 2 π + m2 π 0 ) = αλ 2 Yes: π are composite QCD Today we have 2 naturalness problems: δm 2 h = αλ2 and δv = Λ 4 : 0. Natural or unnatural? If natural, solved by: 1. A new symmetry or composite Higgs?

8 List of solutions What keeps δm 2 h 12g2 top Λ2 top 3(g g 2 )Λ 2 gauge 3λΛ 2 Higgs (4π) 2 < m 2 h? A new symmetry Scalar H H + θ Keeps H massless. Goldstone boson. Vector A µ A µ + µ θ Keeps A µ massless In 5 dims: H = A 5 Higgs has weak-scale size Fermion Ψ e iθγ 5Ψ Keeps Ψ massless. H SUSY Ψ. Technicolour H bound state like π Delay E.g.: heavy higgs Large extra dims H is a string or... The problem is different Higgsless or eaten by vectors Warped extra dims Dual to technicolor Anthropic Life needs m q M Pl

9 How to present? No longer SUSY or SUSY: now many alternatives. Today we need a critical discussion, not a buying list. Why many? Which are the good ones? 1) Select in a politically correct way using SPIRES. 2) Correct removing sociological influences.

10 SPIRES encephalogramme % of papers in hep-ph 10 SUSY technicolor extra dims higgsless? anthropic?? little higgs year nothing at LEP1 SUSY-GUT strings branes no proton decay at SK Λ nothing at LEP2 vacuous landscape nothing at B-factories Trend to balkanization, but 2006 ac 2 blhc. Boom or sboom?

11 Interpreting the encephalogramme New physics is old: studied since 30 years, but no new physics appeared. In these unhealthy situations new directions get influenced by sociology. Relative popularity of different approaches is the combination of three main factors: Plausibility: Is the topic plasuible? Fertility: is there anything new to do? Fashion: is it fun?

12 Critical discussion Plausibility Fertility Fashion Super-symmetry 10% 1% 100% Large extra dimensions 1% 10% 100% Warped extra dimensions 1% 10% 1000% Technicolor 2% 1% 1% Higgsless 1% 10% 10% Gauge/Higgs unification 0.1% 10% 10% Little Higgses 1% 10% 10% LH + T -parity or SUSY 10% 10% 10% Anthropic 100%?? Dark Matter 100% 10% 100% Today there is little to do in SUSY, but it might be a good investment. In the rest, I discuss plausibility, evaluated in 2006, as candidates for LHC

13 Experimental indications? 1) Direct and indirect data showed that the top is heavy, m t 173 GeV 2) Indirect data suggest the existence of a light higgs, m h < 200 GeV This shifts solutions to the hierarchy problem towards lower energies. In the SM, cut-offing top loop at E < Λ cut off δm 2 h δm2 h (top) = 12λ2 top (4π) 2 Λ2 cut off δm 2 h < m2 h if Λ cut off < 400 GeV no longer few TeV! (Bigger Λ cut off needs fine-tuning, which is only a plausibility problem ). Implication for LHC: ligher top (s-top? Vector-top?) But at the same time 3) direct: no new detectable particles, m > 100 GeV. 4) indirect: no new non-renormalizable-operators, Λ > 10 TeV.

14 L eff = L SM + O/Λ 2 NRO Higher dimensional operators O encode the low energy effects of new physics too heavy to be directly seen: form factors,..., quantum gravity. The Higgs is not discovered but is tested, from longitudinal polarization of W, Z Only SU(2) L U(1) Y, B, L, B i, L i, CP symmetric operators O: operator O affects constraint on Λ NRO 1 2 ( Lγ µ τ a L) 2 µ-decay 10 TeV 1 2 ( Lγ µ L) 2 LEP 2 5 TeV H D µ H 2 θ W in M W /M Z 5 TeV (H τ a H)WµνB a µν θ W in Z couplings 8 TeV i(h D µ τ a H)( Lγ µ τ a L) Z couplings 10 TeV i(h D µ H)( Lγ µ L) Z couplings 8 TeV H ( Dλ D λ U λ U γ µνq)f µν b sγ 10 TeV 1 2 ( Qλ U λ U γ µq) 2 B mixing 6 TeV Message: Λ NRO > 10 TeV 400 GeV Λ cut of

15 The little hierarchy problem Solutions with Λ cut off Λ NRO > 10 TeV leave δm 2 h 500m2 h Successes of the SM so boring that a message appears? Maybe just an accidental fine-tuning. Maybe we need to build less invasive models. Maybe we are trying to drag the æther. LHC is like Michelson-Morley: even a null result would be important

16 Doubts Is the Higgs light? Does the Higgs exists? Do we exist? A heavy Higgs delays the hierarchy problem: δm 2 h < m2 h Data: ε 1, ε 3 (m h ). In the SM m h < 200 GeV. In general one must interpret: 10 8 (1) The Higgs seems light because it is light (2) The higgs is heavy or it does not exist, but new physics has enough free parameters that any data can be reproduced. 68, 90, 99% CL (3) / No proposed new physics predicts something else that fakes a light higgs ε ε3 Can we estimate the probability of (2)? BSM? m h = 1, 0.6, 0.4, TeV As long as data become more precise, it becomes more and more unlikely. Today: few % in a generic context. More likely if new physics dominantly affects only ε 1 (and ε 3 ): e.g. technicolor, extra Z 2 -odd higgs doublet,...

17 Scorecards

18 Scorecard of technicolor m h fully stabilized up to the Planck scale. Predicted by strings. Problems with δε N TC N F. Sannino: δε 3 ok in model with small N TC N F (fundamental symmetric). Problems with δε 1 : needs custodial symmetry and top model. No convincing flavour model so far. DM candidates analogous to proton?

19 Scorecard of extra-dimensions Predicted by strings. We do not know what quantum gravity means. Likely, graviton signals are not the main signals. Casadio: black-holes All particles become strings, while at LEP all was point-like. Quantum gravity models do not allow (sharp) conclusions.

20 Scorecard of Higgsless Modest goal: delay breakdown of unitarity to 10 TeV in 5d Too large corrections to precision data (unless fine-tuning complicated enough models)

21 Scorecard of gauge/higgs unification H = A 5 of SU(3) in 5d with 1/R TeV: problems with precision data. Higgs Yukawa couplings gauge couplings. (λ e g,..., λ top > g). Problems alleviated with warped 5d.

22 Scorecard of warped extra dimensions Like extra dimensions + plausible stabilization mechanism. AdS CFT dual to technicolor! Warped extra-dimension 4d renormalization-scale Kaluza-Klein gravitons spin 2 techni-mesons Particle on the Planck brane Elementary Particles elsewhere Composite Randall-Sundrum: all SM on TeV-brane all composite. Contino: 5d as effective description of technicolor with Higgs as Goldstone with custodial symmetry: if v/f 0.1 all computable effects are small enough: Planck brane Bulk TeV brane SU(3) c SU(2) L U(1) Y SU(3) c SO(5) U(1) B L SU(3) c SO(4) U(1) B L LHC: single or double production of KK top partners.

23 Scorecard of SUSY Natural stabilization of m h up to the Planck scale. Λ? Appealing and predicted by strings. MSSM unifies α i. Dimension-5 p decay too fast in minimal GUT. Matter parity needed to avoid dimension-4 p-decay. Precision data almost unaffected. Many DM candidates. DM phenomenology remains dark. Many parameters: could fit 1 anomaly/year for 20 yr. MSSM prediction m h < 120 GeV in trouble. Sparticles not seen at LEP2. lightest higgs mass in GeV excluded by LEP1 excluded by LEP lightest chargino mass in GeV soft terms renormalization scale in GeV Few % of CMSSM parameter space left: vivere pericolosamente

24 Scorecard of little-higgs... Ugly Stabilization of m h only up to 10 TeV Can be used to improve technicolor or SUSY Problems with precision data...with T -parity Avoids problems with precision data. Gives a DM candidate.

25 Higgs as pseudo-goldstone Basic idea: Higgs is a pseudo-goldstone boson of a global symmetry broken at a scale f Happens in QCD, making m 2 π α em 4π Λ2 QCD + m qλ QCD Λ 2 QCD But The Higgs seems not a Goldstone boson: a Goldstone boson π has flat potential: V 0π 2 + 0π 4. we want a small Higgs mass, but we need a sizable coupling: V 0h 2 + λh 4. Simplest attempts lead to m h, m t < M Z and to h f. To proceed anyway one needs to build complex machineries: little Higgs models. λ, λ top generated more than m h thanks to selection rules analogous to m 2 π ± m 2 π 0 = α em 4π Λ2 QCD + 0 Λ QCD m q thanks to ɛ ijk π i π j m k q = 0 implemented by adding appropriate particles

26 The little-higgs mechanism Collective symmetry breaking: a global symmetry often containing two copies of the electroweak gauge group that get spontaneously broken to the SM at a scale f by the combined action of more than a single Higgs field. The top Yukawa can be obtained by mixing with extra vector tops. Basic idea. But the extra particles added to implement the selection rule affect precision data at tree level, such that little-higgs concretely realizes the little hierarchy problem rather than solving it: the same scale Λ f: cuts-off quadratically divergent corrections to m 2 h suppresses higher-order operators. Exceptions: no U(1) Y, g 2 g 2, f 2 f 1, T -parity, super-little, heavy Higgs.

27 The little Higgs is not little enough From a LH perspective, the problem is that one does not get a little Higgs: Naïve pseudo Goldstone: Higgs vev scale of new physics V = (loop)h 2 + (loop)h 4 + (loop)h 6 + h f The top loop can make the quartic big enough that m h > 115 GeV. Little Higgs: V (loop)h 2 + (tree)h 4 h f? f 4π Data disfavor m h 115 GeV, preventing a significant increase in λ. T-parity allows f v, but f is a vev like v: it is not naturally small. Heavy higgs is generically less fine tuned, and exploits the little Higgs [M.Piai] Super-little-Higgs: marriage between pseudo-goldstone and SUSY is difficult but convenient marriage: would solve the FT problems of both: FT problems of SUSY equivalent to m 2 (µ) = 0 renormalized at µ f few TeV. h f could be obtained thanks to m 2 further suppressed by supersymmetry..

28 XAnthropic selection The 3 results that transformed many theorists into anthropists.

29 ❶ V (10 3 ev) 4 0 Dark Energy seems to be just a cosmological constant Λ Another hierarchy problem, with no known solution. Proposed attempts fail for good generic reasons γ CDM? Baryons Age of the universe in year density in ev Λ? Temperature in ev In any case: why V ρ now? Structure form when ρ matter > V, ρ radiation A Λ times bigger will have prevented formation of (our?) galaxy. Caution: really a success? Study galaxies formed at z 10.

30 ❷ The problem of the hierarchy problem δm 2 h < m2 h now calls for new physics below a TeV. But nothing found. Unelegant solutions to an æstetical problem or the weak scale v is anthropically selected? At fixed Yukawas: Increasing v by a few makes m n m p > E B : nuclei decay to H. Reducing v by a few makes m p > m n so that H decays. [Agrawal, Barr, Donoghue, Seckel, 1997] Caution: not yet clearly a problem: LHC will tell? Nightmare for experimentalists: not even the Higgs. For phenomenologists: only the Higgs. For theorists: SUSY with fine-tuning 10 3.

31 ❸ The string demographic explosion Quantum gravity (possibly experimentally irrelevant) was attached hoping that it leads to a unique theory of everything that predicts something at low energy. String theory was promising and gained a strong influence on theorists. 1 M-theory in 11d 5 string theories in 10d 10 O(500) string models in 4d Predictivity is lost when inventing ways of getting rid of the extra dimensions. Dirty physics mostly comes from higher dimensional geography, not from theory. (Possibly not so bad: no realistic string models found so far) Maybe strings gave no results for 30yrs because it provides the right anthropic theory. We can only live in the vacuum that accidentally has small v and Λ. Other unpredictive anthropic models are easily build: V (many Higgs) has 2 many vacua. Caution: alternative?

32 Scorecard of split-super-symmetry Hierarchy problems understood as anthropic, abandoning naturalness. Can be above LHC. Freedom used to build something that phenomenologists and stringists like. Only SUSY fermions: unifies α i avoiding problems with dimension-5 p decay. Z 2 symmetry added to avoid dimension-4 p decay and keep DM stable.

33 Conclusions We need data Perrotta