THE STATUS OF THE BSM SCENARIOS

THE STATUS OF THE BSM SCENARIOS

(AFTER THE FIRST LHC PHASE)

STEFAN POKORSKI, UNIVERSITY OF WARSAW

LHC 7-8 TeV

A GREAT TRIUMPH: 125 GeV HIGGS DISCOVERY

A PARTICLE APPARENTLY JUST AS THE ELEMENTARY HIGGS BOSON PREDICTEDBY THE SM IS DISCOVERED!

„APPARENTLY JUST” IS VERY IMPORTANT!

TO APPRECIATE ALL THAT LET’S REMEMBER THE FOLLOWING….

The Brout-Englert-Higgs mechanism in the gauge theory of electroweak interactions needs additional interactions with spontaneously broken GLOBAL symmetry

e.g SU(2)xSU(2)SU(2)

The BEH mechanism: Goldstone bosons become the longitudinal modes of the gauge bosons W, Z which acquire masses.

Simplest dynamical sector (considered by many as a toy model) with global chiral symmetry (to be spontaneously broken) – self interacting scalar field, a doublet of SU(2)- IS NOW PROMOTED TOA REAL THING

3 Goldstone bosons + physical elementary scalar

GIARDINO ET AL.’13

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IN SM THE HIGGS COUPLINGS TO A PAIR OF FERMIONS OR GAUGE BOSONS ARE IN PROPORTION TO THEIR MASSES

VERY UNLIKELY TO REPRODUCEIT BY ACCIDENT

IT REALLY APPEARS AS THESM HIGGS PARTICLE!

IS THE SM A CONSISTENT THEORY UP TO THE PLANCK SCALE (LIKE e.g. QED)? YES!

RENORMALISABLE

NO LANDAU POLE UP TO Mp

(ALMOST) STABLE VACUUM UP TO Mp

THOSE CONCLUSIONS STRONGLY DEPEND ON

AT LEAST AT THE ELECTROWEAK SCALE, THE SM IS A CORRECT EFFECTIVE THEORY OF ELECTROWEAK INTERACTIONS

THE HIGGS MASS HAPPENS TO BE WELL BELOW THE PERTURBATIVITY LIMIT AND AT THE EDGE OF THE VACUUM STABILITY BOUND (FOR THE TOP MASS AROUND 173 GeV) UP TO THE PLANCK SCALE

IS THE SM A CONSISTENT THEORY UP TO THE PLANCK SCALE?

YES BUT….

ISNT IT INDEED JUST AN EFFECTIVE THEORY, AN APPROXIMATION TO A DEEPER ONE (SIMILARLY AS QED, ALTHOUGH CONSITENT UP TOMp, IS ONLY LOW ENERGY APPROXIMATION TO SM)?

BY THE WAY, RENORMALISABILITY IS A GREAT VIRTUE OF EFFECTIVE THEORIES

less than (3- 5) % deviationsfrom the SM couplings

VERY CHALLANGING: DEVIATIONS MAY BE OF THE ORDER OF THEPRESENT UNCERTAINITIES IN THE SM PREDICTIONS

INDEED, IN SPITE OF NO HINT FOR NP AT THE LHC,DONT RUSH TO A TOO QUICK CONCLUSION ON THE VALIDITY OF THE SM TO PLANCK SCALE BECAUSE:

HIGGS COUPLINGS VERSUS NEW SCALES:

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NO MATTER HOW CHALLANGING IT MAY BE TO SEE BSM PHYSICS THAT WAY,

PRECISION HIGGS (AND TOP) PHYSICS LOOKS NOW LIKE A MUST!

(CLIC, ILC, FCC?)

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EMPIRICAL EVIDENCE FOR BSM: DARK MATTER--THIS IS NOW THE CRUCIAL PROBLEM IN PARTICLEPHYSICS (WITH A PARTICLE PHYSICS SOLUTION?)

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IF THERMAL EQUILIBRUM IN THE EARLY UNIVERSE IS THE SOURCE OF THE DM RELIC ABUNDANCE, THEN THEVALUE

IS THE MAJOR HINT FOR A LOW SCALE NEW PHYSICS !

+ DIRECT DETECTION + LHC -> RELEVANT PARAMETR SPACE BEGINS TO BE TESTED

WHY BSM, IN SPITE OF THE SUCCESS OF SM- CONT…

THE HIGGS PARTICLE WOULD BE THE FIRST EXAMPLE OF AN ELEMENTARY SCALAR PARTICLE!

So far, Nature does not seem to like elementary scalarsand the composite ones are never „unnaturally” light(much lighter than the compositeness scale) unless they are (pseudo) Nambu- Goldstone bosons, like pions in QCD

WHY BSM, IN SPITE OF THE SUCCESS OF SM- CONT…

ANY SHORT DISTANCE PHYSICS THAT COUPLES TO THE HIGGS(RH NEUTRINO, GUT PARTICLES..) WOULD INTRODUCE QUADRATIC SENSITIVITY OF VEV TO THOSE SCALES

NATURALNESS PROBLEM OF THE SM:

STRICTLY SPEAKING, IT IS NOT THE PROBLEM OF QUADRATIC DIVERGENCES IN THE SM:IF NO SCALES EXCEPT V=240 GEV AND IGNORING GRAVITY AS A PHYSICAL CUT-OFF, ONE MAY IGNORE THE PROBLEM (BECAUSE THE SM IS RENORMALISABLE)

IN ADDITION,

Higgs potential in the SM: describes but does not explain dynamically the origin of the Fermi scale

IF IT HAS A DYNAMICAL EXPLANATION, THE SM SHOULD BE EMBEDDED IN A DEEPER THEORY!

OTHERWISE, ANTHROPIC PRINCIPLE HAS TO BE INVOKED? BUT WE NEED ONLY ONE SCALAR. WHAT IF MORE ARE DISCOVERED?

GIVEN THE APPARENT FINAL SUCCESS OF THE SM AND THE ABSENCE OF ANY EVIDENCE FOR NEW PARTICLES (SO FAR)—

HAS THE CASE FOR BSM PHYSICS CLOSE TO THE ELECTROWEAK SCALE CHANGED?

THE MOTIVATION REMAINS INTACT: DARK MATTER ANDTHE QUESTION ABOUT THE ORIGIN OF THE FERMI CONSTANT

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HOPEFULLY, THE SOLUTION TO THE DM IS PART OF A COMPLETE BSM THEORY CLOSE TO THE WEAK SCALE BUT IT IS ALSO CONCEIVEABLE THAT IT IS NOT THE CASE

WITH THE ABOVE GUIDELINE, THERE ARE TWO MAIN DIRECTIONS:

SUPERSYMMETRY COMPOSITE HIGGS MODELS (HIGGS DOUBLET AS A NAMBU- GOLDSTONE BOSON OF A NEW STRONG SECTOR WITH A SUFFICIENTLY BIG SPONTANEOUSLY BROKEN GLOBAL SYMMETRY E.G. SO(5)SO(4)

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BOTH CAN ACCOMMODATE 125 GeV MASS AND ALMOST SM-LIKE COUPLINGS

UNIQUE FEATURE: CANCELLATION OF QUADRATIC SENSITIVITY TO ARBITRARILY HIGH SCALES

………….. ………. + ………. ……. ~

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SUPERSYMMETRY

(FERMION – BOSON CANCELLATIONS)

FOR THE STOP MASS 1 TeV,

SO WE GET 1% FINETUNING IN THE HIGGS POTENTIAL

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FERMION – FERMION CANCELLATIONS!

EXP. SIGNATURES: HEAVY FERMIONS, SPIN 1 VECTOR MESONS

COMPOSITE MODELS CAN ACCOMMODATE 125 GeVHIGGS BOSON

BUT, IT’S A PHYSICAL PICTURE RATHER THAN A REAL MODEL

A LOT OF ARBITRARINESS , NO EASY UV COMPLETION,

ELECTROWEAK SECTOR LINKED TO NON-PERTURBATIVEPHYSICS

ALL THAT CAN BE CONFRONTED WITH THE WELL KNOWN VIRTUES OF SUPERSYMMETRY

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MORE RECENTLY, REVIVAL OF THE IDEA OF CLASSICALLY SCALE INVARIANT SM (BARDEEN-1995)

AT TREE LEVEL; EWSB BY QUANTUMCORRECTIONS-COLEMAN&WEINBERG

ONLY LOGARITHMIC QUANTUM CORRECTIONS; IGNORING GRAVITY AS A PHYSICAL CUT-OFF AND IN CONSEQUENCE IGNORING QUADRATIC DEPENDENCE ON Mp

DIMENSIONAL TRANSMUTATION a LA QCD, EXCEPT THAT IN QCD THERE IS NO ELEMENTARY SCALAR…

CAN ONE ALSO GET DM AND NEUTRINO MASSES IN SUCH ONE SCALE MODEL?

TUNING IN MANY DIMENSIONLESS COUPLING?

THEORETICALLY NOT WELL FOUNDED BUT INTRIGUING, IF A REALISTIC MODELS CAN BE CONSTRUCTED…

TWO THEORIES THAT PREDICT THE HIGGS MASS IN A CERTAIN NARROW RANGE, AS A FUNCTION OF THE TOP MASS

• SM EXTRAPOLATED TO THE PLANCK MASS

• MINIMAL SUPERSYMMETRIC MODEL

AS A FUNCTION OF THE TOP ANDSTOP MASS

TAKE 1 TeV FOR STOPS TO KEEP THE HIGGS POTENTIAL REASONABLY„NATURAL”

NON OBSERVATION OF THE SUPERPARTNERS IS CONSISTENT WITH THE HIGGS MASS BUT AT THE SAME TIME IS PUTTING THE IDEA OF NATURALNESSUNDER CERTAIN PRESSURE

HOWEVER SUSY SEARCHERS ARE STILL QUITE FRAGMENTARY

HIDDEN NATURALNESS? ( STEALTH SUPERSYMMETRY)

Searches for top squarksn Dedicated searches for both direct and indirect production of top squarks; no signs of them

(yet):

u But still room left for naturalness: e.g. M(gluino)~1.5 TeV; m(stop)~300 GeV; m(LSP)~150 GeV

n Really need more energy!

Feb 03, 2014 CERN Accelerator School 27

SUMMARY

THE HIGGS DISCOVERY MAKES THE SM LOOKING AS A CONSISTENT THEORY UP TO VERY HIGH ENERGIES

THE EXPERIMENTAL EXPLORATION OF THE TeV SCALE IS STILL IN A VERY PRELIMINARY STAGE

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BUT THE CASE FOR THE BSM PHYSICS REMAINS INTACT: DARK MATTER AND DYNAMICAL ORIGIN OF THE FERMI CONSTANT. MAY OR MAY NOT BE UNDERSTOOD IN ONE THEORETICAL FRAMEWORK?

SUPERSYMMETRY REMAINS TO BE THE LEADING CANDIDATE

CLASSICALLY SCALE INVARIANT SM (PLUS MINIMAL ADDITIONS)?

END