# Tagged Questions

"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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### 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 ...
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### Before Dark Energy was discovered

I'm really confused on this topic. Pardon my French if my questions seem really stupid. Before Dark Energy was discovered in 1998 did scientists know that the cosmological constant calculated, I ...
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### Why does the flatness problem (of the universe) present a fine tuning problem?

The Friedmann equation can be written $$|\Omega-1|=\frac{|k|}{a^2H^2}$$ In a period where the universe is decelerated $a^2H^2$ becomes bigger as we extrapolate into the past. We know $|\Omega-1|$ ...
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### Does the Peccei-Quinn (PQ) mechanism require fine-tuning?

The strong CP problem: the QCD theta parameter can not be arbitrarily small due to 't Hooft's doctrine of naturalness (a parameter can be arbitrarily small only when putting it to zero provides an ...
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### Precision of the Gravitational Constant [closed]

I went to a theological talk where the speaker, while answering a question on intelligent design, claimed that, if $G$ was different by one part in $10^{120}$,then the universe would either collapse ...
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### Hierarchy problem and quadratic corrections in the Standard Model

In this paper, the third paragraph of the “Introduction” says that the Standard Model by itself is a natural theory. As I understand, they say there is no quadratic divergence in the Standard Model ...
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### Supersymmetry as a solution of hierarchy problem

Hierarchy problem is the statement of why the weak force is much stronger than gravity. In terms of coupling constant, weak force (Fermi coupling) is much larger than gravity (Newton's constant). I ...
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### Why do we need any model beyond SM to fine-tune the Higgs mass?

ATLAS and CMS combined their results recently and it shows that higgs mass is ~125 GeV. Theoretical physicists try to figure out the "low mass" of the Higgs which causes hierarchy problem at high ...
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### Doubts in understanding the role if quantum corrections in the Hierarchy Problem

Trying to understand the Hierarchy problem many questions come to my mind that I am unable to answer due probably to my poor understanding of renormalization. The basic set up of the hierarchy ...
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### If neutron would be lighter by 1 MeV, how stability of Hydrogen could be changed?

In current Universe proton is stable and the following reaction does not go $p + e \rightarrow n + \overline{\nu_e}$ Currently proton is lighter than neutron by 1.293 MeV. If neutron would be ...
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### $d=2$ pole argument of quadratic divergences in Peskin & Schroeder's book

Q1: My question is, in the context of dimensional regularisation(DREG, in dimension $d$), why do they mention the absence of $d=2$ pole in the gauge theory cases[1], whereas the $d=2$ pole is not ...
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### Why is the relative weakness of gravity a problem?

In my physics classes, I remember it being repeated a few times that gravity is a much weaker force than the other three fundamental forces, and being told this is an open problem in physics. However, ...
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### Leonard Susskind said that the small value of the cosmological constant could mean that the universe is much bigger than we thought. Why?

He said that near the beginning of this Youtube video that it could mean that the universe is much bigger than he had thought that it was, and that the cosmological constant wasn't even a constant. I ...
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### How “unnatural” is the universe? [closed]

Looking to read up on the impact the discovery of Higgs boson has on the String Theory I came upon these two paragraphs in an article about the Higgs boson Nobel Prize: One possibility has been ...
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### Finite corrections to the Higgs mass in SUSY

I am worried here about specific supersymmetric scenarios in which an energy scale above the TeV is introduces. An example would be the Seesaw extension of the Minimal Supersymmetric Standard Model. ...
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### Smolin on Cosmological selection and neutron stars

Regarding the cosmological selection hypothesis and testable predictions, Lee Smolin asserted the following: "Smolin: I did make two predictions which were eminently checkable by astrophysical ...
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### Scalar field divergent mass correction interpretation question (hierarchy problem)

Simple power counting tells you that a scalar field coupled to some fermions at one-loop picks up a correction to the mass of the order $\Lambda^2$. Based on this people say things like "it's natural ...
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### Renormalization and the Hierarchy Problem

The hierarchy problem is roughly: A scalar particle such as the Higgs receives quadratically divergent corrections, that have to cancel out delicately with the bare mass to give the observed Higgs ...
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### Can dimensional regularization solve the fine-tuning problem?

I have recently read that the dimensional regularization scheme is "special" because power law divergences are absent. It was argued that power law divergences were unphysical and that there was no ...
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### Multiverse explnation of fine tuning of cosmic constants

Physicists proposed the idea of multiverses to explain extraordinary fine tuning of the cosmic constant and physical laws which is essential for rise of life on earth. Is there any experiment that ...
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### Fine tuning: why is multiverse with anthropic principle considered a better explanation than anthropic principle alone?

I got the impression from several public lectures that, when it comes to the fine tuning problem, physicists tend to give multiverse together with anthropic principle as a plausible solution, but ...
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### Dimensional analysis to estimate order of magnitude of quantities

In the Coursera course From the Big Bang to Dark Energy on several occasions dimensional analysis was used to estimate the scale of quantities. This almost seems like a contradiction in terms to me, ...
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### What are the implications of the Holographic principle?

What are the implications for the Holographic principle? I understand the basics of the principle, the relationship with black holes and string theory but what this is going to tell us? Does it help ...
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### Sharp cut-off, quadratic corrections and naturalness

When introducing the fine-tuning problem, a sharp cut-off as a regulator in the calculation of the Higgs mass corrections is used. Since this regulator breaks translational and gauge invariance, up to ...
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### Fine-Tuning, the Hiearchy Problem, and Mass in the Standard Model

In Chapter 1 of his book String Theory in a Nutshell, Kiritsis states the following. The [Standard M]odel is unstable as we increase the energy (hierarchy problem of mass scales) and the theory ...
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### Categorizing solutions to Hierarchy problem

We know that no gauge symmetry can prevent a term $m_\phi^2|\phi|^2$ for a scalar field, and that, given the quadratic loop corrections, the natural scale is $m_\phi \sim M_P$. This is related to the ...
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### Earliest example of naturalness/fine-tuning arguments

The notion of naturalness is important in particle physics, especially supersymmetry. I was a little surprised, then, that the idea, or at least the name, is apparently only ~30 years old ('t Hooft, ...
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### Has unnaturalness motivated new ideas in physics?

The cosmological constant problem arises because the natural scale of the cosmological constant is $10^{120}$ times larger than what we observe. This implies that the dimensionless constant is much ...
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### How is the hierarchy problem consistent with the decoupling theorem?

One the one hand we have the hierarchy problem in it's various forms, in my understanding in it's most serious form one could state it as the observation that if there is a heavy mass scale M in ...
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### Why is it desirable to have a symmetry to make cosmological constant zero?

It is sometimes stated that absence of a symmetry to make cosmological constant zero is a problem. But observed value of dark energy is very small and non-zero. So why is it desirable to have a ...
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### What is the $\mu$ problem in SUSY?

I need a little bit of help in understanding the mu problem in SUSY. As I understand it, the gist of the problem is that $\mu$ must be on the same order of magnitude as the electroweak scale (246 GeV)....
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### Definition of Fine-Tuning

I've looked in and out the forum, and found no precise definition of the meaning of fine-tuning in physics. QUESTION Is it possible to give a precise definition of fine-tuning? Of course, I guess ...
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### What is the hierarchy problem?

BACKGROUND So far I understood that the hierarchy problem was the large difference between the gravitational scale, $M_{pl}\sim 10^{18}\; [GeV]$, compared with the electroweak scale, \$M_{ew}\sim 10^3\...
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### Relationship between hierarchy problem and higgs fine tuning?

I often hear of hierarchy problem being used synonymous with Higgs fine tuning (esp with regards with motivations for SUSY). What exactly is the relationship between the two problems? As I understand ...
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### On the naturalness problem

I know that there are several questions about the naturalness (or hierarchy or fine-tunning) problem of scalars masses in physics.stackexcange.com, but I have not found answers to any of the following ...
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### Hierarchy is no problem and susy is a mathematical tool for data fitting

I saw this paper in the arXiv: http://arxiv.org/abs/1206.4711. The author seems well-known and has many very well cited papers. But what he says sounds very strange. What I get from this paper are ...
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### Why is Hawking's No Boundary condition described in terms of an instanton if there's no tunneling?

Regarding his take about combining No Boundary proposal with inflation theory (Hawking and Turok), he talks about the "pea instanton". To my very limited understanding I thought instantons were only ...
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### Higgs mass and the hierarchy problem

I was wondering what is the opinion about importance of the hierarchy problem in the hep community? I'm still a student and I don't really understand, why there is so much attention around this issue. ...
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### Fine Tuned Universe

Is the fine tuning that cosmologists talk about (that our Universe is fine tuned for intelligent life) is the same as the fine tuning of the squared mass parameter of the Higgs in the Standard Model? ...