Questions tagged [fine-tuning]

"Fine-tuning" is a situation in which the fundamental parameters in a theory must be "fine-tuned", i.e. precisely chosen, in order for a theory's predictions to agree with experimental data.

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Naturalness problem and Anthropic principle

I heard that the recent LHC results tend to reject natural SUSY, which I understand requires some fine-tuning on the loop corrections of Higgs mass. Here I came up with a naive question: is the ...
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The hierarchy problem: Higgs mass correction from gauge boson loop

From this article Fine Tuning Problem (Perez, Weizmann Institute of Science, Lecture Note) in section C, the hierarchy problem arises from the fact that there are quadratically divergent loop ...
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How SUSY solves the hierarchy problem?

I am struggling to understand the argument for why the introduction of a stop in SUSY can solve the hierarchy problem. The quadratic divergence from the top loop in the higgs mass calculation gives a ...
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Why is the flatness problem a problem?

Friedmann equation states $$ H^2 \equiv \left( \frac{\dot{a}}{a} \right) = \frac{8\pi G \rho}{3} - \frac{k}{a^2} $$ which describes the evolution of the expansion of the universe. Writing $\Omega(t)...
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Does Supersymmetry really assures that the Higgs self-energy contributions cancel out?

The well-known "Supersymmetry Primer" from Stephen Martin explains in his introduction that for the cancellation of the Higgs self-energy diagrams (Fig. 1.1 a + b) generated by fermions and their ...
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How do we know that the universe is really fine-tuned? [duplicate]

How physicists come to the conclusion that the cosmological constant and the other constants are really fine-tuned in a way that if they are changed just a bit, then stars and life won't exist?
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Does our failure to detect neutrinoless double beta decay spell trouble for the seesaw mechanism?

The seesaw mechanism is a theoretical model of neutrino masses that has the side benefit of (arguably) naturally explaining why neutrinos are so much lighter than the other massive Standard Model ...
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MSSM in 2020 and naturalness, state of art?

My question is simple. Given the current LHC and pre-LHC data bounds, can we safely say (an under what odds or conditions) that (pick one) The MSSM is unlikely to be true. The MSSM can yet be true ...
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Are the twentyish constants that have to fall in-between certain ranges to make conditions for live to exist necessary? [closed]

I have been listening to an audiobook about what we cannot know (although I have heard about 20 constants somewhere before that, just can't recall where) and in chapter 9, author talks about twenty ...
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Why is technical naturalness a natural expectation?

In first few minutes of this lecture by Nathaniel Craig, he explains the idea of Dirac naturalness in the following way. Let us consider a QFT as an effective theory with a UV cut-off $\Lambda$. Let $...
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Confusion about choice of renormalization scale in $\overline{\rm MS}$ mass

The $\overline{\rm MS}$ mass is function of the renormalization scale $\mu$. What does it mean to choose this scale $\mu$ as the $\overline{\rm MS}$ mass itself? I am giving some details below to make ...
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Fine-tuning of the cosmological constant (reference request)

It has been claimed in various places on the internet and in books by non-physicists (i.e. by unqualified people) that if the cosmological constant $\Lambda$ had a value different by so much as $10^{-...
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How Supersymmetry solves the hierarchy problem

The fermion contribution to the Higgs mass is $$\Delta m^2_{H}=-\frac{|\lambda_{f}|^2}{8\pi^2}\Lambda^2_{UV}+\dots$$ And the scalar contribution is: $$\Delta m^2_{H}=\frac{\lambda_{s}}{16\pi^2}\...
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What is the justification for Dirac's large numbers hypothesis?

Dirac stated that "Any two of the very large dimensionless numbers occuring in Nature are connected by a simple mathematical relation, in which the coefficients are of the order of magnitude unity." ...
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How the hierarchy of forces is explained by Supersymmetry?

The hierarchy problem is often stated in two ways: First, the divergent corrections to the Higgs bare mass, second, why is gravity so much weaker than the other three forces. The solution to the ...
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Why is the smallness of Higgs mass not technically natural?

Technical naturalness The smallness of a parameter $\theta$ in the Lagrangian of a quantum field theory is said to be technically natural, if in the limit of vanishing $\theta$, the theory has some ...
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How is there no hierarchy problem without UV cutoff?

I can understand the quadratic divergent corrections to Higgs bare mass which is referred to as the hierarchy problem. But I don't understand how there won't be any hierarchy problem if we do not ...
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Does technical naturalness hold only for global symmetries, or also gauge symmetries?

Suppose you have an action $S(\epsilon) = S_1 + S_2 + \epsilon\, S_\mathrm{int}$. Assume that $S_1$ is gauge invariant under the action of the group $G$ and $S_2$ is gauge invariant under the action ...
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What actually is the flatness problem?

One of the Friedman equations is given by $$ H^2\equiv\Big(\frac{\dot{a}}{a}\Big)^2=\frac{8\pi G}{3}\rho-\frac{k}{a^2},\tag{1} $$ which fixes the evolution of $a$ (with given $\rho(t)$) if values for $...
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$\theta$ angle QCD technically natural

Why exactly does the observed smallness of the $\theta$-angle in QCD constitute a fine-tuning problem? I thought that the content of 't Hooft's technical naturalness was exactly that a parameter is ...
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Hierarchy problems: calculating the mass of the Higgs vs. other SM particles

While reading up on hierarchy problems in particle physics (wikipedia), I stumbled onto the statement that in the Standard Model, there is no hierarchy problem (or at least it cannot be formulated) ...
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What really enforces technical naturalness of electron mass?

Technical or 't Hooft naturalness A parameter $\theta$ in the Lagrangian of a field theory is said to be natural, if in the limit of vanishing $\theta$, the theory has some enhanced symmetry. If this ...
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Why is the up quark is lighter than the down quark, while top is heavier than bottom?

Up, charm and top seem to be similar in terms of electric charge (+2/3e) while down, strange and bottom have also same charge (-1/3e). In the second and third family, positively charged quark has ...
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Fine Tuning of the Universe

I'm an A level student looking into the fine tuning of various constants. Physicists explain the extensive effects that would happen if these constants were to be changed/different and hence, how this ...
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Is naturalness meaningful for non-fundamental theories?

Naturalness has been a guiding philosophy for particle physics for a long time, but a few years ago I heard a talk by Nima Arkani-Hamed where he pointed out that it seems to have failed us as it ...
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What happens to the massive gauge bosons in a simple Little Higgs model?

I'm trying to understand a simple Little Higgs (toy) model where the Higgs doublet is made of pseudo Nambu-Goldstone Bosons generated by breaking the symmetry from $SU(3)_L\times U(1)_Y$ to $SU(2)_L\...
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Bound on large extra dimensions using gravitational waves

Are there proposed observations using gravitational waves which put a bound on the size of large extra dimensions (say in the context of ADD model)? The claim in the ADD paper is that you cannot ...
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Estimate of neutrino masses from the values of $\Delta m_{21}^2$ and $\Delta m_{13}^2$ only!

The blog here says that The measured mass differences between the eigenstates are $\Delta m_{21}^2=7.5\times 10^{-5} {\rm eV}^2$ and $\Delta m_{13}^2=2.5\times 10^{-3} {\rm eV}^2$, suggesting that ...
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Hierarchy problem and loop quantum gravity

According to https://en.wikipedia.org/wiki/Hierarchy_problem#Finite_Groups. Hierarchy problem can be theoretically solved using symmetry of certain bosonic string theory on the Leech lattice (though ...
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Why naturalness is an issue in particle physics? It is not in fluid dynamics

I have often heard that naturalness is a strong argument in favor of Supersymmetry. They say that there must be energy scales not too far away the EW-energy so that the quantum corrections of the ...
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Why universe is so perfectly made for us? [duplicate]

I am very eager to learn that, "Why universe is so perfectly made for us?" Or our universe is just stable by chance?
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Why is technical naturalness enough?

There are two notions of "naturalness" used in particle physics today. Dirac naturalness: all dimensionless parameters $g$ in a theory should be order $1$. Technical naturalness: an observed coupling ...
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Are trans-Planckian field values a problem for the relaxion?

The relaxion is a new model-building gadget that solves the hierarchy problem by allowing the Higgs mass term to dynamically relax to zero. To describe it as simply as possible, leaving a lot out: we ...
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What motivates clockwork theory?

Clockwork is a new model-building gadget that produces very small couplings starting from a theory with no small numbers at all, in an attempt to solve the hierarchy problem. To describe it as ...
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Is the universe really “fine-tuned for life”?

I understand what is meant when we say the universe is "fine tuned", but I've seen it claimed it's is fine tuned "for life". Is it? When I look at known or even speculated life in our universe, I see ...
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Why does standard model lose predictivity if it has unstable vacuum?

In String Theory In A Nutshell by Elias Kiritsis, Standard Model is unstable as we increase the energy (hierarchy problem of mass scales) and the theory loses predictivity as one starts moving far ...
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How fine-tuned is the expansion rate and the density of the universe?

I read somewhere that If the expansion rate of the universe were larger or the density of the universe were less , no galaxies would form. If the expansion rate of the universe were smaller or the ...
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The theoretical calculation underlying the cosmological constant problem

The electroweak vacuum energy density is $10^{120}$ times larger than the currently observed value of the dark energy. I have two questions in regard to this statement. $\bullet$ Firstly, what are ...
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Would the existence of leptoquarks solve the hierarchy problem of the Higgs-boson?

Would the existence of leptoquarks solve the hierarchy problem of the Higgs-boson ? According to wikipedia these are assumed to be bosons which could contribute to the cancellation of the vacuum ...
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In BSM model building, what counts as fine tuned?

The Standard Model contains an extreme fine-tuning: the Higgs mass is very small compared to what it would naturally be, by a factor of around $10^{15}$. Lots of theories extending the Standard Model ...
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Is Flatness Problem still a problem since the observable universe is flat but the whole universe can be curved on much larger scale?

When we say the universe is flat, we mean just the observable universe. So that doesn’t mean the shape of the whole universe is also flat (ie. it can be curved on much larger scale) Is Flatness ...
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What deficiencies of the Standard Model does supersymmetry address?

I have been reading up on supersymmetry and how it was developed to fill the supposed gaps presented left by the Standard Model of Particle Physics. What is one main example of this gap?
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A super-positioned boson-fermion particle

Is it possible to extend the standard model with super positioned particles: bosons+fermions at the same time. Instead of 2 dual particles as SUSY suggests, a particle collapses to its supercharge ...
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Does string theory give any values for the predicted “leakage” of gravity into extra spatial dimensions?

Sorry if this is a duplicate. I have read that string theory has a good explanation for the "hierarchy" problem of the force strength disparity between the fundamental forces because as gravity ...
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Understanding the fine-tuning problem related to baryon asymmetry as an initial condition

The reason for not assuming the Baryon asymmetry of the universe as an initial condition is often attributed to the following fine-tuning problem: If the baryon asymmetry had been an initial condition,...
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Naturalness in Physics and fundamental constants

From the "flatness problem" in Cosmology to the "strong CP problem" and "hierarchy problem" in the Model standard, a lot of problems in physics deal with Naturalness: a certain parameter in our theory ...
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How does the naturalness problem of the Higgs mass changes depending on the cut off scale of the Standard Model (SM)?

In this year's paper (check introduction) James D. Wells brings Susskind's 1979 argument that the SM is valid to a very high energy scale, say the Planck scale, $\Lambda \approx M_{Pl} \approx 10^{18} ...
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Why is imposing a symmetry on a theory considered more “natural” than fine-tuning its couplings?

Theories whose behavior would qualitatively change if their couplings were not fine-tuned to particular values are often dismissed as "unnatural" (in high-energy physics) or "unrealistic" (in ...
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Bare Cosmological Constant and Fine-Tuning Problem

Whenever anyone talks about the cosmological constant, they usually cite the difference of $\approx 120$ orders of magnitude between the observed and calculated values for the vacuum energy ($\rho_\...
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Examples of other hierarchy problems

The commonly quoted version of the hierarchy problem (at least, the one that I have heard), is concerned with the surprisingly low mass of the Higgs. We would expect the Higgs mass squared to have ...