Implications et perspectives theoriques

Transcription

1 Implications et perspectives theoriques Riccardo Barbieri SNS and INFN, Pisa 1/26

2 Particle Physics in one page L ST L SM = 1 4 Fa µnf aµn + iȳ 6Dy + D µ h 2 V (h) +y i l ij y j h + h.c. The gauge sector 1 The EWSB sector 2 The flavour sector 3 +N i M ij N j + Dark Matter Baryon Asymmetry The ν-mass sector 4 (if Majorana) (not included in current knowledge of particle physics) Dark Energy 2/26

3 The great empirical evidence for (and from) the gauge sector (for extension, precision, diversity) 2 the distribution of m h w/o the measurements m h (with a similar story for the top discovery in 1994) (and a partially similar story for the W-Z in 1884) 3/26

4 Is it the coronation of the SM or a step on a road still largely unexplored? L ST = D µ h 2 m 2 h 2 h 4 + ij i j h (+ 4 ) how natural? which dynamics, if any? how about the flavour puzzle? (Note: no physical inconsistency!) A paradoxical answer: yes to both alternatives 4/26

5 The flavour puzzle ij i jh (not touched in this lecture) quark and lepton masses quark mixings lepton mixings 5/26 Every element in these pictures accounted for by an ad hoc parameter among the ij What determines this structure? Not easy without observed deviations from the SM

6 About naturalness a dominant paradigm in the last thirty years naturalness 1: m Pl =( c/g N ) 1/ GeV l Pl = /(m Pl c) cm In the current field theory framework: Why there is a large universe ( 10 3 ev << m Pl )? Why there are large objects in it ( )? naturalness 2: m h << m Pl Can we do physics at different scales without knowing the details at shorter distances? Atomic physics Nuclear physics EW physics? physics gravity 6/26 Apparently not at the moment!

7 naturalness 3: Among the many examples that beautifully work so far the electron self energy: e electric 2 E el m e c 2 e r e µ magnetic 2 E mag m e c 2 the positron (a doubling of the d.o.f. at e + x r 3 e x x e e + e + x x e x e e + x x e e r e c e m e 1/3 m e m e 70 MeV 3 MeV (µ = e 2m e c ) ) solves the problem Weisskopf 1939 (M 2 + M 2 0 m 800 GeV ) (M K 0 L M K 0 S m c 2 GeV ) 7/26

8 Back to the Higgs boson What one needs to know: Its quantum numbers:, gauge q.n.s J PC =0 ++ The strength of its interactions with all other particles and with itself Is it natural? Is it elementary or composite? Is it alone or accompanied? 8/26

9 0 + J P =? ( expected) Parity and angular momentum discrimination by angular distribution in decays (pairwise hypothesis tests) h h ZZ 4l /26 the angular momentum looks right the parity looks right

10 The couplings to other particles From a theorist s informal combination of ATLAS&CMS data Giardino, Kannike, Masina, Raidal, Strumia (as many others) 10/26 The coupling-versus-mass linear relation is an absolute prediction of the ST (not exhaustive: ) No Clebsch distorsion: the Higgs boson is (close to) a doublet gg,

11 A natural, not Fine Tuned Higgs boson Mass mostly the top m 2 SM New H = + 0 new states SM + Higgs by an (approximate) symmetry relative to any higher physical scale to which the Higgs boson is possibly coupled If so, explain why the great empirical success of the SM does not depend on unknown short distance physics 11/26

12 Supersymmetry m 2 SM New H = + 0 s-particles The Higgs boson as a pseudogolsdtone m 2 SM New H = + 0 Heavy composite fermions Question: Nothing seen so far. Shouldn t we worry? 12/26 Answer: No theorem but this page still offers the driving criterium

13 The crucial configuration of supersymmetry (introduced well before the LHC) m 2 SM New H = + 0 s-particles GeV g affects the stop masses 1000 t 1, t 2, b L strongest coupling to the Higgs system 500 g t 2 b t1 2 W B μ M Z at tree level 0 13/26 1 orange areas indicative and dependent on how the Higgs boson gets its mass

14 1000 GeV g g 4t, 3t1b, 2t2b 500 g t 2 b t1 W B 2 14/ naively conservatively m g m g 1300 GeV 1000 GeV BR( g g 4b) 4% (tan 10)

15 1000 GeV 500 g t 2 b t1 W B m 2 m ± m 1 15/26 naively conservatively m t GeV m t GeV (with m = GeV )

16 The Higgs boson as a pseudo-goldstone boson (hence a composite rather than a fundamental object) The pion as an analogy: SU(2) L SU(2) R SU(2) I m 2 = m 2 + m 2 0 A new strong sector at the TeV scale 16/26 Like the pion in QCD, the Higgs boson as a quasi GB of a spontaneously broken global symmetry at the TeV

17 More in detail m 2 SM New H = + 0 Heavy composite fermions Heavy composite fermion mass H t L T t R m h m t M T f symmetry breaking scale Most common: Current searches exclude masses below GeV, depending on the charge 17/26

18 A quantitative measure (!?) of naturalness m 2 h am 2 NP < m 2 h model dependent a measure of fine tuning (which exist in nature) fine tuning hard to achieve (some NMSSM gets close) an indicative MSSM LHC now LHC14 (?) 18/26

19 Last but not least: one or more Higgs bosons? The pro s for one: 1. simplicity How about the 12 (18) matter and the 12 (3) vector states? 2. electromagnetism always preserved From 2 to 3 phases only 3. flavour No big reason to be proud of the 4. a single tuning, in case None is better, which often demands more Higgs boson ij 19/26

20 Two ways to attack the problem By direct search pp h =LHC + X decay products By precision measurements of the couplings of the 125 GeV (quasi-standard) Higgs boson H = s H d c H u h 3 S h 2 (the NMSSM example) SH u H d h = c H d + s H u h LHC 20/26 has SM properties

21 Current status of the MSSM MSSM at variable t m H + h 3 H = s H d c H u h = c H d + s H u h LHC excluded by h LHC -signal strenghts excluded by h 3,A 21/26 B, Buttazzo, Kannike, Sala, Tesi 2013

22 NMSSM: Direct search at LHC14 S h h 2 h LHC (gg h 2 ) =0.8 BR(h 2 h 1 h 1 ) 22/26 (changes in the h 1 self coupling by factors 3-4 possible)

23 A projection from the measurements of the signal strenghts of h LHC LHC14 at 300fb 1 with ATLAS/CMS projected errors MSSM The sensitivity region extends up to about 1 TeV for m h2 NMSSM, S-decoupled NMSSM, H-decoupled 23/26

24 The direct search for Dark Matter N N Zµy M gµym = 0 24/26 Zµy M gµg5ym 6= 0

25 DM searches and the Higgs boson exclusion by XENON100 (100 days x 48 kgs) N N 3 events/1.8 backgd Z( N) spin indep. excluded since long time χ N Z χ N χ N h χ N Higgs boson exchange being probed now for m h = 125 GeV 25/26 h( N) cm 2 ( 0.1 ) 2 ( 100GeV m )2 ( 100GeV m h ) 4

26 Conclusion 1. The discovery of the Higgs boson: might be BOTH the coronation of the Standard Theory AND a first step towards unexplored territory 2. Natural or unnatural theories? before accepting a shift of paradigm, useful to be patient and careful 3. One or more Higgs bosons? could be the lightest new particle(s) around 4. What about the flavour puzzle? 26/26 m s, V CKM Y ukawa : a great embarrassment, ij unlikely to be solved without new key data

27 Guess who is Mrs. Tatcher and who is the other guy

28 NMSSM f = H u H d Two independent reasons to consider it: Fayet Add an extra contribution to m 2 hh = m 2 Zc t + 2 v 2 s 2 2 thus allowing for lighter stops 2. Alleviates fine tuning in v for 1 and moderate tan dv 2 dm 2 NMSSM 3 cot 2 versus dv 2 H u dm 2 H u MSSM 4 g 2 green points have better than 5% combined fine-tuning and mess = 20 T ev in the scale invariant NMSSM m t 1 < 1.2 T ev m g < 3 T ev Gherghetta et al 2012

29 Can the extra Higgs bosons of the NMSSM be the lightest new particles around? Assume a negligibly small CPV in the Higgs sector H (H d,h u,s) T = R 12 R 23 R 13 (h 3,h 1,h 2 ) T R H ph Take h 1 = h LHC with m h1 >m h2,m h3 h 1 = c ( s H d + c H u )+s S No susy loops nor invisible decays, like h 1 95%CL on = + /2 95%CL on ( = 0) s 2 =0,.15,.3

30 h 3 H = s H d c H u Current status h = c H d + s H u h LHC MSSM at variable t NMSSM at variable m H + excluded by h LHC -signal strenghts excluded by h 3,A 21/26 B, Buttazzo, Kannike, Sala, Tesi 2013

31 H-decoupled S h h 3 h LHC =0.8 =1.4 sin 2 excluded by h LHC t -signal strenghts 75 GeV almost irrelevant

32 h 3 H = s H d c H u S-decoupled at LHC14 h = c H d + s H u h LHC (gg h 3 ) BR(h 3 b b) m H + = 300 GeV (and correspondingly )

33 A projection from the measurements of the signal strenghts (ATLAS and CMS preliminary) on the mixing angles Now (effective BR inv ) LHC14 at 300fb 1 (central values as in the SM) thanks to Kannike

34 An alternative supersymmetric view only light gauginos m h = ± 0.8 GeV A less motivated (?) but simpler (?) picture Arkani-Hamed, Dimopoulos 2004 Giudice, Strumia 2011 Arkani-Hamed et al 2012 [If, not to overclose the universe by a stable LSP, ] m S <T R SUSY scalars at m S SUSY fermions at TeV m S /GeV gauginos only at TeV m S < T ev Hall et al, 2013

35 What can we expect from (and for) flavour physics? L = i 12 i O i In some cases i T ev, unless some restriction operative Is it possible that... L = i c i 2 i io i with i controlled by symmetries or some dynamics and c i = O(1) and i 4 v 3 T ev strongly interacting EWSB new weakly int. particle(s) at v Flavour EWSB

36 Breaking of flavour symmetries embedded in few basic parameters U(3) Q U(3) u U(3) d U(3) 3 Y u =(3, 3, 1) Y d =(3, 1, 3) (MFV) Chivukula, Georgi 1987 (TC) Hall, Randall 1990 (SUSY) D Ambrosio et al 2002 (general) U(2) Q U(2) u U(2) d U(2) 3 B, Isidori et al 2011 (general) Y u,y d split under U(2) 3 - representations Y u = t u V Q V T u 1 Y d = b d V T d V Q 1 Requiring a small breaking of U(2) 3 : V = V Q V Q V = O(V cb ) and, by consistency with flavour data, V u, V d << V U(3) 3 at large tan U(2) 3 Feldmann, Mannel 2008 Kagan et al 2009

37 The F =2 case U(3) 3 U(2) 3 c LL 2 2 ij 1 2 ( d Li µ d Lj ) 2 ij = V ti V tj c K LL ds 2 ( d L µ s L ) 2 c B LL ei B ib 2 ( d Li µ b L ) 2 (cannot fit the discrepancy ) B, Buttazzo et al 2012 Flavour tests versus direct searches (cum grano salis) for c =1 4 (m, f) E.g. c (3 T ev/ ) means m, f 0.8 T ev

38 F =1 Summary Chirality breaking (cromo-)magnetic operators B X (s,d) B K( )µµ U(3) 3 U(2) 3 B Chirality conserving op.s X (s,d) B K( )µµ U(2) 3 } B s µµ [K ] correlated no phase in U(3) 3

39 F =2 key measurements K V ub V cb M d M d = SM = 34.5 ± 3.0 M s M s M d exp =35.0 ± 0.3 M s U(2) SM centered on K M d M s The key role of and S V ub as well as of F Bd,s (B d,s ) 1/2 from the lattice S KS S V ub = V ub = Buras, Girrbach 2012

40 What if the Higgs boson likes to be unnatural and the SM is unchanged up to very high energies? largest couplings Higgs self-coupling Degrassi et al 2012 Chetyrkin, Zoller 2005 Bezrukov et al 2005

41 A special meaning for λ 0 at MPl? M t Assume SM unchanged up to M Pl Nielsen et al 1988 Shaposhnikov et al 2009 M h Degrassi et al M Pl ( (M Pl ) 0) Absolute stability at not quite achieved for current best values of M t and M h Speculations about possible meaning of all this not lacking (anthropic pressure,...)

42 What s the real evidence for (M Pl ) (M Pl )=0? g 2 t g 4 t g t Even if this improved (, etc) how shall we know that it is not a coincidence? Thanks to Rattazzi and Strumia