This is a note concentrate on the log average Sarnak conjecture, after the work of Matomaki and Raziwill on the estimate of multiplication function of short interval. Given a overview of the presented tools and method dealing with this conjectue.

**1. Introduction **

Sarnak conjecture \cite{Sarnak} assert that for any obersevable come from a determination systems , where , . The correlation of it and the Liuvillou function is 0, i.e. they are orthongonal to each other, more preseicesly it is just to say,

This is a very natural raised conjecture, Liuville function is the presentation of primes, due to we always believe the distribution of primes in should be randomness.

It has been known as observed by Landau \cite{Laudau} that the simplest case,

already equivalent to the prime number theorem. It is not difficult to deduce the spetial case of Sarnak conjecture when with the obersevation in $latex {(1)}&fg=000000$ come from finite dynamic system is equivalent to the prime number theorem in athremetic progress by the similar argument. Besides this two classical result, may be the first new result was established by Davenport,

Theorem 1Let , is a inrational, then the obersevation come from is orthogonal to Mobius function. due to is a basis of , suffice to proof,

There is a lots of spetial situations of Sarnak’s conjecture have been established, The parts I mainly cared is the following:

- Interval exchange map.
- Skew product flow.
- Obersevable come from One dimensional zero entropy flow.
- Nilsequences.

But in this note, I do not want to explain the tecnical and tools to establish this result, but considering an equivalent conjecture of Sarnak conjecture, named Chowla conjecture, and explain the underlying insight of the suitable weak statement, i.e. the log average Chowla conjecture and the underlying insight of it.

The note is organized as following way, in the next section $latex {(2)}&fg=000000$, we give a self-contained introduction on the tools called Bourgain-Sarnak-Ziegler critation, explain the relationship of this critation and the sum-product phenomenon, also given some more general critation along the philosephy use in establish the Bourgain-Sarnak-Ziegler critation, which maybe useful in following development combine with some other tools. The key point is transform the sum from linear sum to bilinear sum and decomposition the bilinear sum into diagonal part and off-diagonal part, use the assume in the critation to argue the off-diagonal part is small and on the orther hand the diagonal part is also small by the trivial estimate and the volume of diogonal is small, this is very similar to a suitable Caderon-Zugmund decomposition.

In section $latex {(4)}&fg=000000$, I try to give a proof sketch of the result of Matomaki and Raziwill, which is also a key tools to understanding the Sarnak conjecture, or equivalent the Chowla conjecture. The key points of the proof contains following:

- Find a suitable fourier indentity
- Construct a multiplication-addition dense subset , and proof that the theorem MR hold we need only to proof it hold for instead of
- Involve the power of euler product formula. divide the whole interval into a lot of small interval with smaller and smaller scale and a residue part. We look the part come from every small scale as a major term and look the residue part as minor term.
- Deal with the major term at every scale, by a combitorios identity and second moments method.
- find a enough decay estimate from a scale to the next smaller scale.
- Deal with the minor term by the H… lemma.

Due to the theorem of MR do not exausted the method they developed, we trying to make some more result with their method, Tao and Matomaki attain the average version of Chowla conjecture is true by this way, and combine this argument and the entropy decresment argument they established the 2 partten of the log average Chowla conjecture is true. Very recently Tao and his coperator proved the odd partten case of log average chowla conjecture is true, combine an argument of frustenberg crresponding principle and entopy decresment argument. But it seems the even and large than 2 case is much difficult and seems need something new to combine with the method of MR and entropy decresment and frunstenberg corresponfing principle to make some progress.

So, in section $latex {(5)}&fg=000000$, we give a self-contain introduction to the entropy decresment argument of Tao, and combine with the frustenberg corresponding principle.

In the last section $latex {(6)}&fg=000000$, I state some result and method and phylosphy of them I get on nilsequences and wish to combine them with the previous method to make some progress on log average Chowla conjecture on the even partten case.

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**2. Bourgain-Sarnak-Zieglar creation **

We begin with the easiest one, this is the main result established in \cite{BSZ}, I try to give the main ideal under the proof, but with a no quantitative version is the following,

Theorem 2 (Bourgain-Sarnak-Zieglar creation, not quantitative version)if for all primes we have:

Then for multiplication function we have

Remark 1For simplify we identify .

The idea is following, break the sum into a bilinear one, so, of course, we multiplication it with itself. i.e. we consider to control,

To control 4, we need exhausted the mutiplication property of , we have . We can not get good estimate for all term,

The condition in our hand if following,

So, just like the situation of Cotlar-Stein lemma \cite{Cotlar-Stein lemma}, we wish to estimate like following:

Then we consider divide the sum into diagonal part and non-diagonal part, as following,

But the first part is small, i.e.

Because of

and the second part is small, i.e.

Because diagonal part is small in and trivial inequality

But the method in remark 2 is not always make sense in any situation, we need to construct two suitable sets and then break up into , this mean,

But this could be construct in this situation, thanks to the prime number theorem,

Morally speaking, this is the statement that the primes, which is the generator of multiplication function, is not very sparse.

**3. Van der curpurt trick **

There is the statement of Van der carport theorem:

Theorem 4 (Van der curpurt trick)Given a sequences in , if , is uniformly distributed, then is uniformly distributed.

I do not know how to establish this theorem with no extra condition, but this result is true at least for polynomial flow. \newpage *Proof:*

This type of trick could also establish the following result, which could be understand as a discretization of the Vinegradov lemma.

Remark 3Uniformly distribution result of : Given , coverages to a uniformly distribution in as .

Remark 4But I definitely do not know how to establish the similar result when .

Remark 5This trick could also help to establish estimate of correlation of low complexity sequences and multiplicative function, such as result:

Maybe with the help of B-Z-S theorem.

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**4. Matomaki and Raziwill’s work **

In this section we explain the main idea underlying the paper \cite{KAISA MATOMA 虉KI AND MAKSYM RADZIWILL}. But play with a toy model, i.e. the corresponding corollary of the original result on Liouville鈥檚 function.

Remark 6

is equivalent to the prime number theorem 3.

The most important beakgrouth of analytic number theory is the new understanding of multiplication function on share interval, this result is established by Kaisa Matom盲ki and Maksym Radziwill. Two very young and intelligent superstars.

The main theorem in them article is :

Theorem 6 (Matomaki,Radziwill)As soon as when , one has:

for almost all .

In my understanding of the result, the main strategy is:

- Parseval indetity, transform to Dirchelet polynomial.
- Involved by multiplication property, spectral decomposition.
- From linear to multilinear , Cauchy schwarz inequality.
- major term estimate.
- Estimate the contribution of area which is not filled.

** 4.1. Parseval indetity, transform to Dirchelet polynomial **

We wish to establish the equality,

This is the norm, by Chebyschev inequality, this could be control by norm, so we only need to establish the following,

We wish to transform from the discretization sum to a continue sum, that is,

Remark 7There are two points to understand why 19 and 18 are the same.

- .
- and is to make that .

Now we try to transform 19 by Parseval indetity, this is something about the norms of the quality we wish to charge. It is just trying to understanding 19 as a quantity in physical space by a more chargeable quality in frequency space. Image,

Then . Note that,

So by Parseval identity, we have,

Remark 8We know the Fejer kernel satisfied,

So morally speaking, we get the following identity.

In fact we do a cutoff, the quality we really consider is just:

established the monotonically inequality:

Theorem 7 (Paserval type identity)

Remark 9In my understanding, This is a perspective of the quality, due to the quality is a multiplicative function integral on a domain with additive structure, it could be looked as a lots of wave with the periodic given by primes, so we could do a orthogonal decomposition in the fractional space, try to prove the cutoff is a error term and we get such a monotonically inequality.

But at once we get the monotonically inequality, we could look it as a聽compactification process and this process still carry most of the information so lead to the inequality.

It seems something similar occur in the attack of the moments estimate of zeta function by the second author. And it is also could be looked as something similar to the 聽spectral decomposition with some basis come from multiplication generators, i.e. primes.

** 4.2. Involved by multiplication property, spectral decomposition **

I called it is “spectral decomposition”, but this is not very exact. Anyway, the thing I want to say is that for multiplication function , we have Euler-product formula:

But anyway, we do not use the whole power of multiplication just use it on primes, i.e. leads to following result:

This is a identity about the function , the point is it is not just use the multiplication at a point,i.e. , but take average at a area which is natural generated and compatible with multiplication, this identity carry a lot of information of the multiplicative property. Which is crucial to get a good estimate for the quality we consider about.

** 4.3. From linear to multilinear , Cauchy schwarz **

Now, we do not use one sets , but use several sets which is carefully chosen. And we do not consider [X,2X] with linear structure anymore , instead reconsider the decomposition:

On every it equipped with a bilinear structure. And is a very small set, which is in fact have much better estimate.

Now we just use a Cauchy-Schwarz:

** 4.4. major term estimate **

** 4.5. estimate the contribution of area which is not filled **

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**5. Entropy dcrement argument **

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**6. Correlation with nilsequences **

I wish to establish the following estimate: is the liouville function we wish the following estimate is true.

Where we have as ,

is a compact space.

I do not know how to prove this but this is result is valuable to consider, because by a Fourier identity we could transform the difficulty of (log average) Chowla conjecture to this type of result.

There is some clue to show this type of result could be true, the first one is the result established by Matomaki and Raziwill in 2015:

Theorem 8 (multiplication function in short interval)is a multiplicative function, i.e. . as , then we have the following result,

And there also exists the result which could be established by Vinagrodov estimate and B-S-Z critation :

Theorem 9 (correlation of multiplication function and nil-sequences in long interval)is a multiplicative function, i.e. . is a polynomial function then we have the following result,

\newpage {9} \bibitem{Sarnak} Peter Sarnak, Mobius Randomness and Dynamics.

\texttt{https://publications.ias.edu/sites/default/files/Mahler }. \bibitem{Laudau} JA 虂NOS PINTZ (BUDAPEST). *LANDAU鈥橲 PROBLEMS ON PRIMES*.

\texttt{https://users.renyi.hu/~pintz/pjapr.pdf} \bibitem{BSZ} Knuth: Computers and Typesetting,

\texttt{http://www-cs-faculty.stanford.edu/\~{}uno/abcde.html}

\bibitem{Cotlar-Stein lemma} Almost orthogonality

\texttt{https://hxypqr.wordpress.com/2017/12/18/almost-orthogonality/}

\bibitem{KAISA MATOMA 虉KI AND MAKSYM RADZIWILL} KAISA MATOMA 虉KI AND MAKSYM RADZIWIL, MULTIPLICATIVE FUNCTIONS IN SHORT INTERVALS.

\texttt{https://arxiv.org/abs/1501.04585v4/}.

It seems that several formulas here are broken.

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