# Joe Lykken's 19 March talk at Cern

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## Main Question or Discussion Point

Summary slide at the end (thanks to Peter Woit for flagging this talk as interesting):

==quote Lykken==
￼Summary
• There is no SUSY
• There is no naturalness problem
• There is no input Higgs potential: EWSB is generated radiatively
• All masses come from dimensional transmutation and whatever is going on in the dark sector
• There will be discoveries from the LHC and direct dark matter detection confirming this picture.
==endquote==

I've heard a strong expectation expressed that the next 10 years will turn out to be "the Dark Matter decade". Astrophysical evidence for DM has been getting more varied and detailed. It's not unreasonable to expect that we will learn considerably more about it. There could be direct detection in the next 10 years.

Since there is 5 times more DM than OM (ordinary matter) the DM sector seems likely to be important to understanding matter and could lead to major change in the Standard Model.
============

Lykken sounded a MINIMALIST note earlier in the talk, and cited a paper by Meissner and Nicolai which I seem to recall being cited in a Mitchell Porter thread.
To put it simply "minimalism" is the idea that the Standard Model (with a small change to take care of DM) could be OK all the way to Planck scale. I.e. no new physics from here to Planck scale---big desert. Lykken considered this viewpoint and cited the Meissner Nicolai paper, though in the end he did not seem to come down there.

Maybe someone who follows this more closely wants to comment.

Here are the slides:
http://indico.cern.ch/getFile.py/ac...nId=1&resId=0&materialId=slides&confId=217732

Related Beyond the Standard Model News on Phys.org
atyy
Some think naturalness is not important, but Lykken and Meissner and Nicolai both don't think so.

Lykken says the SM may be natural.

Meissner and Nicolai propose that classical conformal symmetry, rather than supersymmetry, may be what solves the naturalness problem.

In that sense, the motivation for supersymmetry is not misguided. It simply is not a unique solution to the problem.

(String are a completely different motivation for supersymmetry, but at a different scale.)

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Hi Atyy,
you mentioned strings. Lykken used to be a string theorist:
==quote==

Showing results 76 through 85 (of 85 total) for au:Lykken

76. arXiv:hep-th/9603133 [pdf, ps, other]
Weak Scale Superstrings
Joseph D. Lykken
Journal-ref: Phys.Rev.D54:3693-3697,1996
Subjects: High Energy Physics - Theory (hep-th); High Energy Physics - Phenomenology (hep-ph)

77. arXiv:hep-ph/9511456 [pdf, ps, other]
Four-Dimensional Superstring Models
Joseph D. Lykken
Subjects: High Energy Physics - Phenomenology (hep-ph)

78. arXiv:hep-th/9510241 [pdf, ps, other]
Three Generations in the Fermionic Construction
Shyamoli Chaudhuri, George Hockney, Joseph D. Lykken
Journal-ref: Nucl.Phys. B469 (1996) 357-386
Subjects: High Energy Physics - Theory (hep-th)

79. arXiv:hep-th/9505054 [pdf, ps, other]
Maximally Supersymmetric String Theories in D<10
Shyamoli Chaudhuri, G. Hockney, Joseph D. Lykken
Comments: LaTex, 10 pages. Additional details of the solutions described here are available on the World-Wide Web at this http URL
Journal-ref: Phys.Rev.Lett.75:2264-2267,1995
Subjects: High Energy Physics - Theory (hep-th); High Energy Physics - Phenomenology (hep-ph)

80. arXiv:hep-ph/9501361 [pdf, ps, other]
String Consistency for Unified Model Building
S. Chaudhuri, S.-wei Chung, G. Hockney, J. Lykken
Comments: harvmac (available from xxx.lanl.gov), 30 pages (reduced format), if you are using harvmac for the first time, make sure to adjust the "site dependent options" at the beginning of the harvmac file. Shortened introduction and added table 3, listing the complete massless spectrum with U(1) charges of Model A. Version to appear in journal
Journal-ref: Nucl.Phys. B456 (1995) 89-129
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

81. arXiv:hep-th/9409151 [pdf, ps, other]
String Models for Locally Supersymmetric Grand Unification
S. Chaudhuri, S.-W. Chung, G. Hockney, J. Lykken
Subjects: High Energy Physics - Theory (hep-th); High Energy Physics - Phenomenology (hep-ph)

82. arXiv:hep-ph/9405374 [pdf, ps, other]
Fermion Masses from Superstring Models with Adjoint Scalars
Shyamoli Chaudhuri, Stephen-wei Chung, Joseph D. Lykken
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

83. arXiv:hep-ph/9309258 [pdf, ps, other]
Planck-Scale Unification and Dynamical Symmetry Breaking
Joseph D. Lykken, Scott Willenbrock
Journal-ref: Phys.Rev. D49 (1994) 4902-4907
Subjects: High Energy Physics - Phenomenology (hep-ph)

84. arXiv:hep-th/9212126 [pdf, ps, other]
Exact Path Integrals by Equivariant Cohomology
Hans Dykstra, Joe Lykken, Eric Raiten
Journal-ref: Phys.Lett. B302 (1993) 223-229
Subjects: High Energy Physics - Theory (hep-th)

85. arXiv:hep-th/9206107 [pdf, ps, other]
String Theory, Black Holes, and SL(2,R) Current Algebra
Shyamoli Chaudhuri, Joseph D. Lykken
Journal-ref: Nucl.Phys. B396 (1993) 270-302
Subjects: High Energy Physics - Theory (hep-th)
==endquote==

You could say the same thing about that as what you said about Supersymmetry. It was one proposed solution to certain problems, and looked promising, but probably is not the only or the right solution. As you said "the motivation was not misguided" at the time smart people like Lykken were investigating it.

It looks like after 2004 or so he was gradually pulling out of the String program but his work still heavily involved Supersymmetry.
And now in 2013 he seems ready to abandon the assumption of Supersymmetry as well.

atyy
So is it correct that the SM is natural after all?

Funnily, he uses dimensional regularization , which I'd naively thought was the most unphysical.

Googling around, I found http://www.physics.mcgill.ca/~jcline/qft1b.pdf which has the intriguing statement "It is as though DR automatically provides the counterterms to exactly cancel the quadratic divergences, and only exhibits the logarithmic ones. This might seem like a way of avoiding the hierarchy problem for the Higgs boson mass, but our experience with the p-space cutoff tells us that the quadratic divergences must really be there, even if DR does not see them."

Last edited:
fzero
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So is it correct that the SM is natural after all?

Funnily, he uses dimensional regularization , which I'd naively thought was the most unphysical.

Googling around, I found http://www.physics.mcgill.ca/~jcline/qft1b.pdf which has the intriguing statement "It is as though DR automatically provides the counterterms to exactly cancel the quadratic divergences, and only exhibits the logarithmic ones. This might seem like a way of avoiding the hierarchy problem for the Higgs boson mass, but our experience with the p-space cutoff tells us that the quadratic divergences must really be there, even if DR does not see them."
I don't believe that DR makes quadratic divergences go away at all. It's just that it makes all UV divergences look the same, namely as the singularities in the gamma function. A logarithmic divergence looks like

$$\int \frac{d^{4-\epsilon}k}{ (k^2+m^2)^2} \sim \Gamma(\tfrac{\epsilon}{2}) \sim \frac{1}{\epsilon} + \mathrm{finite} ,$$

while a quadratic divergence looks like

$$\int \frac{d^{4-\epsilon}k}{ k^2+m^2 } \sim \Gamma(-1+\tfrac{\epsilon}{2} )\sim \frac{1}{\epsilon} + \mathrm{finite} ,$$

after we use the identity ##\Gamma(x) = (x-1)\Gamma(x-1)##. So we can say that DR softens the higher-degree divergences, but does not remove them.

At Peter Woit's blog, "Alex" and "BB" have a discussion bearing, not just on Lykken's ideas, but also on Shaposhnikov-Wetterich and (implicitly) Nicolai-Meissner. Unfortunately, it is likely to be impenetrable if you don't already know some of the concepts of effective field theory, e.g. relevant and irrelevant operators and their scaling dimensions.

But basically, "BB" is saying that the that the Lagrangian of Lykken's field theory will need to be augmented with some extra terms, describing effective interactions induced by new physics at the Planck scale. As Wikipedia says, each term in the Lagrangian must have a dimension of mass to the fourth power, so if the scaling dimension n of these extra induced operators is not automatically equal to four, there will need to be a coefficient of the form (mass)(4-n), and apriori we expect (mass) to be around mPlanck.

So, when the scaling dimension n of the induced operator is greater than four, this coefficient will be an inverse power of the Planck mass, and the new effect will be tiny - "irrelevant". But when n is less than four, the coefficient will be huge and the new effect will be "relevant" for observable physics far below the Planck scale. A standard way out of this, as "BB" remarks, is for a new symmetry to completely rule out the term in question. Another way would be for the RG flow at high energies to have some special property, like asymptotic safety, which sets special boundary conditions at the Planck-scale cutoff. And the final alternative, which is not really a serious option, would be to say that the coefficient just happens to come out tiny, by sheer coincidence. The exact value of the coefficient arises from the details of Planck-scale physics; saying that it will be about a power of the Planck mass is just an order-of-magnitude estimate.

I haven't processed the argument that the SM looks natural from the perspective of dimensional regularization, and can't comment on how it would affect the conventional position, as enunciated by "BB".

fzero
Homework Helper
Gold Member
At Peter Woit's blog, "Alex" and "BB" have a discussion bearing, not just on Lykken's ideas, but also on Shaposhnikov-Wetterich and (implicitly) Nicolai-Meissner. Unfortunately, it is likely to be impenetrable if you don't already know some of the concepts of effective field theory, e.g. relevant and irrelevant operators and their scaling dimensions.

But basically, "BB" is saying that the that the Lagrangian of Lykken's field theory will need to be augmented with some extra terms, describing effective interactions induced by new physics at the Planck scale. As Wikipedia says, each term in the Lagrangian must have a dimension of mass to the fourth power, so if the scaling dimension n of these extra induced operators is not automatically equal to four, there will need to be a coefficient of the form (mass)(4-n), and apriori we expect (mass) to be around mPlanck.

So, when the scaling dimension n of the induced operator is greater than four, this coefficient will be an inverse power of the Planck mass, and the new effect will be tiny - "irrelevant". But when n is less than four, the coefficient will be huge and the new effect will be "relevant" for observable physics far below the Planck scale. A standard way out of this, as "BB" remarks, is for a new symmetry to completely rule out the term in question. Another way would be for the RG flow at high energies to have some special property, like asymptotic safety, which sets special boundary conditions at the Planck-scale cutoff. And the final alternative, which is not really a serious option, would be to say that the coefficient just happens to come out tiny, by sheer coincidence. The exact value of the coefficient arises from the details of Planck-scale physics; saying that it will be about a power of the Planck mass is just an order-of-magnitude estimate.

I haven't processed the argument that the SM looks natural from the perspective of dimensional regularization, and can't comment on how it would affect the conventional position, as enunciated by "BB".
I have not looked at the exchange that you reference, but I thought that these Higgs-portal models already explicitly assume that there is a UV boundary condition in the form of a conformal fixed point at some scale ##M_\mathrm{conf} \leq M_P##. So there are no relevant operators in the Lagrangian at the high scale. The hidden-sector scalar is assumed to be charged under some ##U(1)## gauge field (it sounds like this is taken to be ##B=L## in some models) and via the Coleman-Weinberg mechanism, this ##U(1)## is spontaneously broken and scale invariance is broken by dimensional transmutation. The symmetry breaking by radiative corrections keeps the low energy scale small with respect to the UV fixed point.

Questions like, is the generated scale small enough to explain the hierarchy and whether we can embed this UV fixed point in some sort of GUT scenario, probably haven't been worked out yet.

There's a paper today by Satoshi Iso, who is cited in Lykken's talk as developing exactly the sort of B-L model that fzero mentions. Here is an earlier paper. Here is a thesis where the minimal B-L extension to the standard model is described in some detail, in chapter 2. Presumably what Iso et al do is to take that exact lagrangian, and set the boundary condition "Higgs quartic coupling equals zero at the Planck scale", and the claim is that Coleman-Weinberg then works and that we get a Higgs of 126 GeV.

(I'm noticing that PF's new style makes embedded links hard to see; that's what the brash red text is for...)

arivero
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Given that the polemic paper in this month (May) SciAm comes from Lykken itself, is it perhaps time to review the success of his proposal?

MTd2
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Supposing that the 7keV line is due dark matter decay, even if it is a new particle, it is a bit too much jumping into conclusions. It could just be some be some overlooked effect from GR, or semi classical GR, like graviton gravtion scattering.